The first secondary-school chemistry textbooks appeared in the second the criteria for assessing the quality of secondary-school chemistry textbooks. PDF | The teaching of chemistry in Serbia as a separate subject dates from The first secondary-school chemistry textbooks appeared in. 𝗣𝗗𝗙 | This study evaluated the Chemistry Textbooks in use in Nigerian performance of the Nigerian secondary school students in chemistry is dwindling.
|Language:||English, German, Portuguese|
|Genre:||Science & Research|
|ePub File Size:||24.52 MB|
|PDF File Size:||10.49 MB|
|Distribution:||Free* [*Registration needed]|
The whole range of senior school certificate examination (SSCE) syllabus has been Senior Secondary Chemistry Textbook 2 Lagos Longman Publishers. New School Chemistry By Osei Yaw Ababio Free PDF eBook Download Form Popularity download chemistry textbook for senior secondary school form. Fill Online. Excellent reviews. Form Popularity osei yaw ababio chemistry textbook pdf form. Get, Create, Make and Sign new school chemistry pdf. Fill Online.
In terms of dominance, after the symbolic were macroscopic representations. It is also important to note that, this is not to suggest an emphasis on depiction of representations at the macro level, but that textbook designers should rather make visual or image representations that are abstract, real and observable to students. The results of Nyachwaya and Wood's study contradicts this finding, with a low indication of macroscopic representations.
We assume that what accounts for this difference is that Nyachwaya and Wood evaluated advance physical chemistry textbooks, which predominantly featured symbolic representations.
In addition, the results of our study indicated a very small proportion of sub-microscopic representations in the textbooks and this fail to address the important point that many chemical phenomena are understood at the particulate level Gilbert and Treagust, Having established the critical role played by the sub-microscopic level in helping students develop mental images of intangible concepts, it becomes equally important that textbook authors and publishers give adequate attention to this form of representation.
Similarly, in a study on how visuals that focus on the particulate nature of matter are used in middle school science textbooks, Kapici and Acikalin-Savasci also reported a less frequent use of the sub-microscopic levels in chemical explanations.
The use of integrated representations in textbooks, such as the multiple and hybrid were infrequent. While multiple and hybrid representations were the fewest, there was not a single mixed representation. However, our results indicate a low prevalence of multiple representations, but rather higher prevalence of the discrete levels, which Treagust et al. Given the role played by these representations in aiding conceptual understanding of chemical concepts, it is a cause for concern that authors, and publishers have not responded to the request for substantial integration of sub-microscopic, multiple, hybrid and mixed representations in the textbooks NERDC, The application of the second criterion on relatedness of representations to text content reveals significant findings.
They are significant because, even though, there are representations that were completely related to the text content, the representations were not linked. Only about This indicates that authors included representations in textbooks without paying sufficient attention to how these representations could best be linked to the text content.
The importance of relatedness of text to representations in terms of completeness and linkage is that readers do not have to try to establish a link and interpret the image in relation to the text by themselves Pozzer-Ardenghi and Roth, Once there is a cognitive overload occasioned by partial or unlinked representations, students could become discouraged and eventually shutdown.
It is not impossible that students could also make incorrect interpretations of images that are not related or linked to the text content Kapici and Acikalin-Savasci, The proximity should be such that they are within the same page. As Wu and Shah suggested, text and the accompanying representations should be presented close together, so that students can easily understand the association between them.
The germaneness of image captions in textbooks relates to the explanation these give to the entire representation and the understanding they convey to readers. Our findings indicated that more than half of the visuals had suitable captions. However, there were also images with problematic captions that did not clearly portray the understanding the visuals were meant to convey.
The existence of images without captions was minimal. Conclusion The study of chemistry largely involves chemical phenomena that are not open to direct observation. Chemistry as a visual science, therefore, requires the integration of chemical representations to depict these phenomena in textbooks and during classroom instructions, for effective teaching and learning of chemical concepts to take place.
Where the teacher may be limited in portraying these phenomena in two-or three-dimensional representations during instruction, the textbook becomes a vital and indispensable tool for conveying an adequate understanding of the underlying concepts and principles of a chemical phenomenon under investigation.
The overarching goal of this study was to investigate how chemical phenomena are represented in chemistry textbooks, through the types and dominant representations, the relatedness and linkage of images or visuals to the text content and the suitability of captions that link images to texts. The findings that have emerged from this study, particularly the dominance of symbolic representations over the other representations, the comparatively fewer examples of hybrid and multiple representations; and the non-existence of mixed representations should raise serious concerns for chemistry educators within the geographical context of this study.
Our results showed the prevalence of symbolic representations and insufficient integration of two or more levels of chemical representations to depict phenomena. Salta and Tzougraki, , we can conclude that, students who use these textbooks may experience similar difficulties in trying to make sense of the chemical concepts depicted by symbolic representations.
Given that these results are very similar to those of other international studies Gkitzia et al. In this way, teachers who understand the role of chemical representations may also be able to use textbooks to scaffold meaningful learning at each level, particularly at the sub-microscopic level, and then assist students to understand the different levels of chemistry.
It is equally important that curriculum developers and textbook writers affirm these representations in the chemistry curriculum and provide teachers with the necessary support for them to reflect on the representations and emphasize chemical concepts at the different levels in chemistry classes. For instance, if teachers present the concept of kinetic molecular theory of matter to students and use the combination of macroscopic, sub-microscopic and symbolic representations, students can observe the phenomenon under investigation, develop conceptual understanding from the explanation of the phenomenon, and be able to symbolize the phenomenon effectively.
Teachers should explore other alternative resources such as conceptual models or computer-based 2D or 3D models, and the internet to provide rich experiences for students to develop mental images of intangible phenomena which can foster meaningful understanding of chemistry.
Conflicts of interest There are no conflicts of interest to declare. Appendix 1 Examples of representations for criterion analyzed and coded in this study.
The image was used to represent how salt is produce from sea water by evaporation. An example of a sub-microscopic representation taken from New School Chemistry textbook. It was used to portray the structure of an atom. An example of a symbolic representation taken Comprehensive Chemistry for Senior Secondary Schools textbook. An example of a hybrid representation taken from New School chemistry textbook.
It was used to represent lattice structure of sodium chloride. It depicts the reaction between hydrogen and chlorine gases to form hydrogen chloride gas at symbolic and sub-microscopic levels. The symbolic and sub-microscopic representations are also placed in parallel so that students can understand their links. The pictures illustrate that as time goes, on the concentration of the solution decreases.
Therefore, it is completely related. An example of a representation that is completely related but unlinked. The image is placed in an experiment and stands right next to the text that explains the experimental procedure. Therefore, it is unlinked. The image is considered to be partially related and unlinked. A collection of notes and worksheets in pdf format in two unit sets, one for honors, and the other for Regents Chemistry. Each unit begins with a nicely-organized set of definitions and notes, and contines with worksheets that can serve as student homework.
Although directed at the high school, these materials can serve as a good review for college chemistry students. Purdue University General Chemistry Topics - Notes and practice problems on a large number of topics. ChemSpider "is a free chemical structure database providing fast text and structure search access to over 58 million structures from hundreds of data sources.
In , I created a list of some of the better videos that I considered worth recommnding to others. One site speciallity is the structure and naming of organic compounds. ChemistryCoach is a high school course support page of enclyclopedic proportions.
Authored by Bob Jacobs of Wilton High School, this well-organized site contains hundreds of links that will be of interest to students at both the high school and first-year college levels.
ChemThink - This new site consists of a series of interactive quiz-based tutorials. There are also some laboratory simulatons. Registration is required, but is free. Look in the left-hand frame to see what topics are available. Merlin's Principles of Alchemy is a chemistry hypertextbook in the form of a large set of HTML files that users download and then view with their Web browsers off-line.
It is organized in an interesting way, and is intended to support users having a wide range of backgrounds and capabilities, including home-schoolers and adult learners.
There is a nominal charge for downloading the material. Quantum theory and the atom - a well-organized and understandable set of Web pages covering quantum mechanics and its applications, including such practical ones as cat scans and microwave ovens.
Well worth a look! Virtual Chemistry Experiments - a collection of interative web-based chemistry tutorials. The tutorials employ Physlets and Chemistry Applets to simulate experiments or depict molecular and atomic structure. Topics include equilibria, kinetics, coordination chemistry, and crystal structure. The halogens show great similarity in their properties e. Group 0: Helium He , Neon Ne , Argon Ar , are the familiar members of this group which are commonly referred to as rare gases or noble gases.
They have no bonding electrons because the outermost shell is completely filled hence the group name zero. Members of the group exhibit similar properties which are different from those of the halogens that come before them and alkali metals that come after them.
This is a confirmation that the end of a period has been reached. All the transition elements have the following characteristics. You should have learned that when elements are arranged in order of increasing atomic number, certain properties recur at regular intervals.
Furthermore, you should have learned that the periodic table of elements serve to justify the trend of behaviour exhibited by elements. It has served to introduce you to the periodic Table. The units that follow shall use the atomic orbital model to further justify the classification and explain the gradation of properties of elements based on the periodic table. Atomic Orbital Model. You have learned in unit 2 about the contributions of Rutherford and Bohr to atomic structure in order to obtain a model of the atom.
Their contributions went a long way to explain some of the observation about the atom. The Rutherford's model of an atom as consisting of a central positively charged nucleus and the negatively charged electrons some distance away from the nucleus, is still acceptable.
However, classical electromagnetic theory denies the possibility of any stable electron orbits around the nucleus. In Bohr's model of the atom, the electron was restricted to being found in a definite regions i. In the Wave Mechanics Model, however, there is a slight chance that the electron may be located at distances other than in the restricted orbits.
Despite this, we still accept Bohr's scheme for quantisation of energy in the atom and that the lowest energy level of the atom is the most stable state. Although Bohr's contribution was remarkable, particularly his quantisation of energy, theory to explain the spectral lines for hydrogen atom; it has the following limitations: The present day picture of the atom is based on wave mechanical or quantum mechanical treatment.
The treatment reflects on the wave-nature of the electron and the quantisation of energy in the atom. Although these treatments are fundamentally mathematical in nature, it describes the electron as point charge and that the density of the cloud at a specified point gives only the probability of finding electrons at that point. We shall look at how this new thinking will help our understanding of the atom and the observed relation between electronic arrangement in atoms and the chemical behaviour of elements.
The quantum theory attempts to understand how electrons are arranged in the atom based on wave and quantum mechanics treatment. The electron is visualised as a point charge.
The density of this point charge varies in different locations around the nucleus and gives a measure of the probability of finding the electron at a specified point. The region or space, around the nucleus, in which an electron in a given energy level is most likely or probable to be found is defined as an orbital. So rather than describing a fixed Bohr orbit in which electrons are located, the modem theory gives a probability description of atomic orbitals.
The results of the quantum mechanical treatment of the atom is summarised below. This designation is retained in the quantum model but to represent distinct energy levels and not shells or orbits.
In otherwords, the quantum model recognises different quantised energy levels around the nucleus. Each principal quantum number n corresponds to a particular energy level and has integral values of 1, 2, 3, 4, etc. Electron with the largest 'n' value has the most energy and occupies the highest energy level; and therefore the most easily removable or ionisable electron. The maximum possible number of electrons in an energy level is given by 2n2.
Log in to Wiley Online Library
The subsidiary quantum number, 1, has integral values ranging from 0, 1, 2, Table 7. Number of sub-levels Names of the sub-levels ,-.
Rather, the location of electron is defined in terms of probabilities which is described by the orbital. A region in space where there is a high probability of finding an electron in an atom is called an orbital.
The density cloud of the electrons defines the shape of the orbital. The electrons that move about to produce a spherical symmetrical cloud around the nucleus is an s- electron residing in an s-orbital.
The p-electrons move about three axes, x, y and z that are at right angles to one another, producing a dumb-bell cloud around the nucleus along each axes. They are called the p-orbitals and are distinguished from each other by N, Py and Pz in line with the direction of the electron cloud. The geometrical representation of the d and f orbitals are more complex and beyond the scope of this programme.
However, before we can apply the quantum numbers to express the electronic configuration of atoms, there are two important rules that you should be familiar with. The principle simply means two electrons in an atom cannot behave in an identical manner. The way in which electrons are arranged in an atom is determined by the order of the sub-levels on a scale of increasing energy level. This is so because electrons are found in the lowest possible energy level, the ground state which is the most stable state of an atom.
A simple representation of the orbitals on an energy scale is given in Fig. The number of orbitals and maximum electrons in the sub-level Value of I Name of Values of m Number of Number of Maximum number sub-level values of m orbitals of electrons 0 s 0 One One 2 1 p 1, 0, —1 Three Three 6 2 d 2, 1, 0, —1, —2 Five Five 10 3 f 3, 2, 1, 0, —1, —2, —3 Seven Seven 14 Starting with hydrogen, which has an atomic number of 1, the electron occupies the Is sub-level and this process of electronic occupation continues with increased atomic number according to the order of increasing orbital energy levels.
To keep a check on the spin of the electron, arrows of opposite spins are used to distinguish two electrons in an orbital. One of the advantages of the electronic configuration of elements using quantum numbers is that it showed the basis for the periodic classification of element. In other words, the key to the periodicity of elements lies in the electronic configurations of their atoms.
The orbital arrangement of electrons clearly showed the great usefulness of the Period Table as it explains the groups and characteristic properties of elements. The correlations between electronic configuration and the physical and chemical behaviour of elements will be discussed in details in subsequent units.
This is a follow up to what you learned about Rutherford and Bohr models of the atom. You should have also learned that the position of electrons can be defined only in terms of the probability of finding it in a region in space referred to as orbitals.
Furthermore, you learned about the four quantum numbers used for characterising an electron. You need to be aware of how to write the orbital electronic configurations of elements based on these four quantum numbers. It has served to introduce you to orbital electronic configuration.
The unit on Period Table II shall build upon this treatment of the electrons in the atoms of elements. Senior Secondary Chemistry Textbook 3 Lagos.
New School Chemsiny. Gradations of Atomic Properties 8. Introduction The periodic table consists of elements arranged in groups and periods based on their atomic number. The number of electrons in a neutral atom of an element gives the atomic number. The electrons occupy electronic shells. The elements in any period have the same number of electronic shells and the number of valence electrons increases progressively by one across the period from left to right.
When elements are arranged in this way, it was observed that the properties of elements recur at regular intervals.
That is, the properties of the elements are a periodic function of their atomic number. The periodic properties give rise to vertical columns of groups or families of elements with the same number of outer or valence elements. The elements in any group have closely related physical and chemical properties.
One great advantage of this, is that it is only necessary to learn the properties of each group rather than the properties of each individual element. Recall that the Bohr theory of shells was the basis for the arrangement of electrons in atoms. Recent discover; r:: The electrons in atoms are now believed to occupy regions in space around the nucleus called orbitals rather than fixed shells.
Orbitals are simply regions in space around the nucleus where the probability of finding an electron is high, they are usually denoted by s,p;d, and f- orbitals. Recall the Pauli's exclusion principle and Hund's rule in the arrangement of electrons in the energy levels. The summary below will refresh your memory. The modern periodic classification The Periodic Table groups atoms of the element according to their electronic configurations. Elements with one s electron in their outer shell are called Group I the alkali metals and elements with two s electrons in their outer shell are called Group H the alkaline earth metals.
These two groups are known as the s block elements, because their properties result from the presence of s electrons. Elements with three electrons in their outer shell two s electrons and onep electron are called Group III, and similarly Group IV elements have four outer electrons, Group V elements have five outer electrons, Group VI elements have six outer electrons and Group VII elements have seven outer electrons.
Group 0 elementS have a full outer shell of electrons so that the next shell is empty; hence the group name. Groups III, IV, V, VI, VII and 0 all have p orbitals filled and because their properties are dependent on the presence ofp electrons, they are called jointly the p block elements, In a similar way, elements where d orbitals are being filled are called the 61 block, or transition elements.
In these, d electrons are being added to the penultimate shell one shell before the outer shell. Finally, elements where f orbitals are filling are called the f block, and here the f electrons are entering the antepenultimate ot second shell from the outer shell shell. A summary of the block arrangement of elements based on the outermost energy levels for s- and p- block elements; and the orbitals being filled for d- and f- block elements. Instead of listing the elements, the periodic table arranges them into several rows or periods, in such a way that each row begins with an alkali metal and ends with an inert gas.
The sequence in which the various energy levels are filled determines the number of elements in each period, and the periodic table can be divided into four main regions according to whether the s,p,d or f levels are being filled. The similarity of properties within a group and the relation between the group and the electron structure is emphasized.
The d block elements are referred to as the transition elements since they are situated between the s and p blocks. Hydrogen and helium differ from the rest of the elements because there are no p orbitals in the first shell.
Helium obviously belongs to Group 0, the inert gases, which are chemically inactive because their outer shell of electrons is full. Hydrogen is more difficult to place in a group. It could be included in Group I because it has one s electron in its outer shell, or in Group VII because it is one electron short of a complete shell. Hydrogen is included in both these groups in the periodic table, although it resembles neither the alkali metals nor the halogens very closely.
The unique properties of hydrogen are largely due to the extremely small size of hydrogen atoms. Thus there is a case for placing hydrogen in a group on its own, or omitting it from the periodic table altogether. The periodic table therefore provides an organized structure to the knowledge and understanding the chemistry of the elements.
Apart from this, there is also a variation of atomic properties of elements in the periodic table. Some of these properties are atomic and ionic sizes, ionization energy, electron affinity and electronegativity. However with the aid of modem techniques such as X-ray and electron diffraction, it is possible to determine the distance between covalently bonded atoms. For example, the distance between the nuclei of oxygen atoms in an oxygen molecule is 0. The atomic radius or sizes of any atom is taken to be one-half the distance of closest approach between the nuclei of atoms in the elemental substance.
In other words, as the atomic number increases across any period, the size of the atom decreases. Recall that as we move across a period one electron is added increasingly from one element to the next and the electrons are being added to the same shell at about the same distance. At the same time, protons are also being added to the nucleus. Increase in the number of proton, increases the nuclear charge which progressively exert a stronger attraction upon the electrons around it and would pull them towards the nuclei.
As the nuclear charge increases with atomic number across a period, the attractive force exerted by the nucleus on the outermost electrons of the atom increases hence the atomic radius or size decreases across a period. For example, on moving from Lithium to beryllium, the number of charges on the nucleus is increased by one, so that all the orbital electrons are pulled in closer to the nucleus.
In a given period, the alkali, metal is the largest atom and the halogen the smallest. Table 8. Recall the lithium in period 2 has two shells; sodium in period 3 has three shells while potassium in period 4 has four shells.
Conditions of Use
In general, as we go down the group, atomic size increases with atomic number see Table 8. The size of an ion called ionic radii is different from atomic sizes. Ionic sizes are measured in electrovalent compounds. The ionic radius of a given compound is the distance between the centre of one ion and the centre of its nearest neighbour of opposite charge.
A positive ion is formed by removing one or more electrons from an atom. When this happens, the number of positive nuclear charge is more than the number of negative electronic charge, hence the electrons are pulled in. A positive ion is therefore smaller than the corresponding atom and the more electrons removed that is, the greater the charge on the ion , the smaller it becomes e.
The number of positive nuclear charge is now less than the number of negative electronic charge hence the pull on the electrons is reduced. In general, ionic radii of negative ions are greater than the corresponding atomic radii i. Ionization energy If energy is supplied to an atom, electrons may be promoted to a higher energy level. If sufficient energy is supplied, the electron may be completely removed, giving a positive ion.
Since it is possible to remove one, two or three E 2nd I. E 3rd I. Across a period, the first ionization energy increases as atomic number increases since the atomic radius decreases.
As the distance decreases, the attraction of the positive nucleus for the electron will increase, hence more energy is required to remove the outermost electron hence the ionization energy will increase.
Note that the screening effect remain almost the same across a period since electrons are added to the same shell. Table 3 shows the first ionization energies of the first twenty elements. Atomic radi i the first These show a general upward trend from Li to Ne and from Na to Ar.
The values for Ne and Ar are the highest in their periods because it requires a great deal of energy to break a stable filled shell of electrons. There are several irregularities. The high values for Be and Mg are attributed to the stability of a filled s for N and P indicate that a half-filled p level is also particularly stable.
The values forlevel. E 2ad I. Fig 8. First ionization energies of the elements in the first two short periods.
This trend is shown with the alkali, metals from Li to Na to K The energy released when an extra electron is added to a neutral gasesous atom to form a univalent negative ion is termed the electron affinity. Since energy is given off in the process, electron affinity has a negative value. Electron affinities depend on the size and effective nuclear charge of the atom.
Moving from left to right across a period, electron affinities decreases i. Down a group of the periodic table, electron affinities increase i. The reason for the observed trend is that atoms with smaller atomic radii tend to have a stronger attraction for electrons and thus form negative ions more readily. The tendency of an atom in a molecule to attract bonded electrons to itself is termed the electronegativity of the atom.
Generally, small atoms attract electrons due to closeness of the nucleus more than large ones and are therefore more electronegative. Atoms with nearly filled shells of electrons will tend to have higher electrcnegativity because of the desire to have a stable filled shell than those with sparsely occupied shells. The electronegativities of elements decrease down a group and increase across a period. The reason for the trend is that down the group, atomic size increases and effective nuclear charge decreases hence electron attracting power electronegativity of the atom decreases.
Hm... Are You a Human?
From left to right of a period, the opposite effect is observed, atomic size decreases and effective nuclear charge increases, these combine to increase electronegativity. The most electronegative elements are the reactive non-metals e.
Fluorine at the top right-hand corner of the periodic table while the least electronegative elements are the reactive metals e. See Table 8. Electronegativity volume roup 1 2 3 4 5 6 7 0 Period H H He 1 2. You should have also observed how this periodic properties vary down a group and across the period of a Periodic Table.
You need to be aware of the reasoning behind the observed trend. It has served to introduce you to the variation of atomic properties - atomic size and radius, ionization energy, electron affinity.
African-Fep Publishers. A chemical reaction takes place always between large number of reactant particles.
The products that are formed also contain a large number of product particles. Chemists therefore use a large number of particles as a base unit when comparing amounts of different substances reacting or are formed in chemical reactions. This basic unit is the mole and the mole concept is one of the most important concepts in Chemistry. The mole concept is applicable to all chemical processes. In this unit the mole will be defined and the concept applied to chemical calculations involving masses and volumes of chemical substances.
Now 0. The elementary particles may be molecules, atoms, ions, electron etc and must be specified. Avogadro number has been determined experimentally and is 6. A very large number indeed. A mole of a substance therefore provides a quantity of material that can be measured for use in the laboratory. The molar mass of a compound is the number of grams of the compound needed to make up one mole of the compound i.
With this new definition of the mole you can calculate the number of i moles ii particles iii atoms etc in a given mass of a substance of known formula.
Table 9. The concept of a mole is central in this type of calculations. The mass of the magnesium oxide is found to be 0. Example 2 Zinc oxide is found by chemical analysis to contain Determine the formula of zinc oxide. Solution Assuming we analyse g sample. Example 3 2.
What is the simplest formula of mercury oxide. Given that the atomic mass of oxygen is 16, determine the atomic mass of X. A balanced chemical equation of the reaction is all that is required. The percentage yield gives the ratio of the experimental yield to a theoretical yield assuming complete reaction. Take the Iasi example Suppose 3. This is called molar volume. Now consider the reaction in the last section. In the next unit the use of mole concept in volumetric analysis and solution preparations will be discussed.
Learn to use the mole concept and you will be in a position to solve a mole of problems. The mole concept is applicable to gas reactions as well as reactions with solid and liquid substances. The mole is a measurable quantity of substance and is more relevant to experiments in quantitative analysis. Give the number of moles of atoms in the following: The percentage composition by mass of a compound of sodium, sulphur and oxygen are Water of crystallisation is 50 percent by mass.
Senior Secondary Chemistry Textbook 1. Africana-Fep Publishers. The mole concept is particularly useful in predicting yield and calculating yield from experiments. This is very important for industrial or la' oratory processes that involve reversible reactions.
Yield and yield percent calculations allow chemists to assess the efficiency of chemical processes and look for ways of improvement where applicable and possible. In this unit we continue our discussion of the mole concept. Applications in solution preparation, volumetric analysis and electrolysis will be the focus.
More calculation using the mole concept to assess the efficiency of some processes will also be discussed. A molar solution is prepared by dissolving one mole of the solute in small amount of the solvent and then make the solution up to 1.
A molar solution can also be prepared from amount less than or equal to one mole of the solute. Example It is required to prepare The solute and solvent are weighed and mixed in the stated proportions. The final volume of solution is immaterial. Note From the definitions and methods of preparation, both solutions are not the same. The preparation of solutions in volumetric titrimetric analysis is done in standard volumetric flasks and solution concentrations are expressed in mol dm-3 Not all solutions are molar solutions.
The concentration of a solution is calculated from the amount of solute and the volume of solution. Example Calculate the concentration of a solution containing 8. You must remember that though a solution has one concentration, the amount of solute will be different for different volumes of the solution. A volume of sea water will taste the same whether you test a cup of it or a bucket or a drop.
The amount of salt you recover from sea water however depends on the volume of sea water evaporated. Example Calculate the amount of sodium chloride recoverable from i 1. Concentration of sodium chloride in the sea water is 0. Solution a i 1. From the average titre the calculation of the concentration is done using mole concept.
Example Calculate the percentage purity of the sodium hydroxide sample. Mole concept allows for calculation to know how much solvent must be added to get the required concentration. Dilution becomes the only way of making dilute solution of common acids that are available commercially as concentrated acids e. Substituting Example What volume of water must be added to cm 3 of a 0.
The Faraday is quantity of charge carried by 1 mole 6. In these calculations the Faraday is used as base unit of electricity. Example 4, cov'ombs of electricity passed in an electrolysis process. The volume of hydrogen gas liberated was 0. Calculate the efficiency of the electrolysis process. Solution 1 Faraday E 6. More applications of the concept will still be in subsequent units. It is hoped that the examples in these two units will assist you in subsequent units where you will be required to use the concept in calculations.
The mole concept is used to asses the efficiency of an electrolytic process. A solution contains 2. Calculate the atomic mass of and identify M. New School Chemistry New Edition. No one has ever seen an atom or a molecule. None of the most powerful microscopes known to us can help us see such particles. Matter exists in three states. These states are solid, liquid and gas.
Ice, water and steam are good examples of these states. Let us take a state like the solid state. The particles in the solid are tightly connected together by forces of cohesion.
The forces holding the particles of a solid restrict their movement, so that they are held in fixed positions. Solids have defmite shapes and volumes and are very difficult to compress. Liquids are hard to compress, have no definite shape but posses definite volumes. A gas occupies the whole volume of the container, has no definite shape and is very compressible.
Can you explain why if a bottle of perfume is opened at one end of a room, the smell is perceived all over the room? The kinetic theory explains the differences in the behaviour of matter in different states. The changes that occur when matter is heated are also explained by the theory.
The kinetic energy of a body is the energy it possesses as a result of its motion. The higher the velocity of a body, the higher its kinetic energy. Can you now explain why accidents with very fast moving bodies cars, stones etc are very fatal? In any given sample of matter, some molecules have very high energies while some have very low kinetic energies. The average kinetic energy of the particles increases with increasing temperature of the matter.
A suspension of sulphur powder in water when viewed under a microscope will demonstrate Brownian motion. Brown was the first scientist to observe this behaviour, hence the name Brownian motion. Diffusion occurs in solids, liquids and gases. A drop of liquid bromine in a closed jar of air vaporises and spreads evenly throughout the jar. A crystal of a soluble coloured solid when dropped in water will after sometime colour the entire volume of water. CuSO 4. Diffusion is fastest in gases and slowest with solids.
The swelling of bean seed in water is an example of osmosis. All the above evidences confirm that particles of matter are in motion as postulated by the kinetic theory.
Because of the strong cohesive force, the particles are held in fixed positions and can only rotate or vibrate about a mean position. This explains why solids have definite shapes and volumes and are very difficult to compress e.
The particles in the liquid state are further apart than in the solid.
The kinetic energy of the liquid particles is higher and particles are not fixed in positions. There is some motion that allows the liquid to maintain a fixed volume but no fixed shape e g ethanol, water and kerosene. In the gas state the particles are in constant random motion in all directions at very high velocities.
There is virtually no force of attraction between the particles explaining why a gas diffuses freely filling all available space. A gas has no definite shape or volume. The large empty spaces between the gas particles explain why gases are very compress Fig I.
On the other hand gas molecules are in perpetual and random motion at very high velocities because of lack of cohesive forces between the particles. When solid matter is heated, the average kinetic energy of the particles increases and changes in the nature of matter occurs from solid-liquid-gas At a temperature characteristic of a particular solid, the particles that are fixed in position acquire sufficient energy kinetic energy to overcome the cohesive force keeping them in fixed positions.
So the solid gradually change to the liquid form. The temperature at which this happens is called the melting point of the solid and the phenomenon is called melting. The melting point is characteristic of the solid and is often used as a criterion of purity for the solid substance.
A pure solid will have a sharp melting point i. As the temperature increases the particles acquire sufficient energy to overcome the cohesive energy of the liquid state.
The particles become free, move more randomly independent of each other. The liquid has gradually been turned to gas vapour. This is vaporisation. The temperature at which there is massive vaporisation from within the bulk of the liquid is the boiling point.
At the boiling point, vapour molecules escape from the inside of the containing vessel to the surrounding space. The boiling point is also a criterion of purity for liquid substances. Again pure liquids have a sharp boiling point. For instance the boiling point of water is C but vaporisation can take place below that temperature. This is evaporation. Evaporation is most rapid at the boiling because the liquid particles have maximum kinetic energies. Evaporation also occurs at temperatures below the boiling point.
This is most likely when a liquid sample is placed in an open container. The high energy particles on the liquid surface can vaporise into the surrounding space.
The loss of high energy particles from the liquid surface will result in a decrease in the liquid volume as well as a decrease in the average kinetic energy of the liquid sample. What is the effect of evaporation below the boiling point on liquid temperature? When the gas cools it returns directly to the solid state. This process is called sublimation and is a useful method for separating a mixture of substances when only one of the substances sublimes, e.
Fig This is a typical heating graph. This energy which is not used to raise the temperature is called the latent heat of vaporisation and the latent heat of fusion at the boiling and melting points respectively. The latent heat is used to supply the particles energy to overcome the cohesive forces in the liquid or solid state.
When the substance cools the reverse changes occur. As the vapour condenses and the liquid freezes the lalent heats are evolved. With virtually no attractive force between the gas particles you should expect the physical behaviour of gases to be much different from those of the solids and liquids. This special behaviour of gases will be the subject of the next two units.
When matter is heated change of state occurs. The kinetic theory explains this as the result of the higher average kinetic energy of the particles at the higher temperature. Melting and boiling occur at temperature characteristics of the matter. These temperatures are called melting and boiling point respectively. Arrange A,B,C,D in the order of increasing melting point. Give a reason for your order of arrangement. Can you recall the following as explained in that unit9 Melting point, boiling point, vaporisation and condensation.
You will also recall that particles in the gas state are in random motion in all directions and at very high speed with virtually no force of attraction between the particles. The physical behaviour of a gas is very much different from those of the solid and liquid.
This physical behaviour of gases was investigated by early scientists and that led to the establishment of gas laws named after them. There is a need therefore to increase the postulates of the kinetic theory to account for the special behaviour of gases. This is the first of two units on gases and you will learn about Boyle's law and Charles' law and the general gas equation. Statement of the gas laws will be examined and the gas behaviour as established by each law explained by the kinetic molecular theory.
There is virtually no force of attraction between gas molecules Gas molecules move independent of each other.
These assumptions are only true for an ideal gas. They constitute what is called the kinetic molecular theory. They specifically deal with the gas molecules. These following six statements describe the behaviour of an ideal gas , 1. A gas consists of small identical particles called molecules moving randomly in all directions colliding with each other and also with the walls of the containing vessel. There is no force of attraction between the gas molecules.
Molecular collisions are perfectly elastic i e no energy is lost when molecules collide with each other or with the container wall. The vol nue of gas molecules is negligible compared to the container volume.
The co. The temperature of the gas is directly proportional to the average kinetic energy of the molecules.The kinetic energy of a body is the energy it possesses as a result of its motion. The next are the macroscopic representations For the atom matter to be electrically neutral, the number of protons must equal the number of electrons. A gas occupies the whole volume of the container, has no definite shape and is very compressible.
This special behaviour of gases will be the subject of the next two units. This is vaporisation. The changes that occur when matter is heated are also explained by the theory.