Some basic concepts of Chemistry
Assignment -1
Definition:-
1. Chemistry :-Chemistry is the science of atoms, molecules and their transformations.
It can also be defined as that branch of science that deals with the study of the composition, properties and interaction of matter.
2. Pure substance :-Pure substances have fixed composition.
For example: - Copper, silver, gold, water, glucose are some examples of pure substances.
Also, the constituents of pure substances cannot be separated by simple physical methods.
3. Elements:-An element consists of only one type of particles. These particles may be atoms or molecules.
For example: - Sodium (Na), copper (Cu), silver (Ag), hydrogen (H), oxygen (O) atoms etc. They contain only one type of atoms.
4. Compounds:-When two or more atoms of different elements combine, the molecule of a compound is obtained.
For example: - Water (H20), Ammonia (NH3), Sugar, carbon dioxide (CO2).
Constituents of a compound cannot be separated into simpler substances by physical methods. They can be separated by chemical methods.
5. Mixtures:-A mixture contains two or more substances present in it (in any ratio) which are called its components.
6. Mass:-Mass is defined as the amount of matter present in a substance.It is constant
7. Volume:- Space occupied by matter is called its volume. It has the units of (length) 3. So in SI system, volume has units of m3.
8. Meter:- The meter is the length of the path travelled by light in vaccum during a time interval of 1/299792458 of a second.
9. Homogeneous mixture:-In homogeneous mixture, the components completely mix with each other and its composition is uniform throughout.
For example: - Air, Sugar solution.
10. Heterogeneous mixture:-In heterogeneous mixtures, the composition is not uniform throughout and sometimes the different components can be observed.
For example: - Mixture of dal mot and bhujia, badam etc.
The components of a mixture can be separated by using physical methods such as simple hand picking, filtration, crystallisation, distillation etc.
11. Physical Properties:- They are those properties which can be measured or observed without changing the identity or the composition of the substance.
Some examples of physical properties are colour, odour, melting point, boiling point, density etc.
12. Chemical properties:- They are those properties which can be measured or observed without changing the identity or the composition of the substance.
Some examples of physical properties are colour, odour, melting point, boiling point, density etc.
13. Weight:-Weight is defined as the force exerted by the gravity on an object. It may vary from one place to another due to change in gravity.
14. Density:-Density of a substance is its amount of mass per unit volume.
SI unit of density = kg/m3.
15. Temperature:- Measure of hottest or coldness of an object is called temperature. There are three common scales to measure temperature — °C (degree Celsius), °F (degree Fahrenheit) and K (kelvin). Here K is the unit SI unit.
The temperatures on two scales are related to each other by the following relationship:-
°F = (9/5) (°C) + 32
The Kelvin scale is related to Celsius scale as follows:-
K =°C + 273.15
16. Atomic mass:-Atomic mass is the mass of the atom.
17. Average atomic mass:- mass of an atom based upon the existence of its isotopes is called average atomic mass.
18. Molecular mass:-Molecular mass is the sum of atomic masses of the elements present in a molecule.
For example:-Molecular mass of methane CH4 = (12.011 u) + 4 (1.008 u) = 16.043 u.
19. Formula mass:- Formula mass is the sum of all the atomic masses of all the constituents of the formula.
20. Molar mass :-The mass of one mole of a substance in grams is called its molar mass.
The molar mass in grams is numerically equal to atomic /molecular/formula mass in u.
21. Limiting reagent:-In a chemical reaction, reactant which is present in the lesser amount gets consumed after sometime and after that no further reaction takes place whatever be the amount of the other reactant present. Hence, the reactant which gets consumed, limits the amount of product formed and is, therefore, called the limiting reagent.
22. Mass % or weight % :-Mass percentage is one way of representing the concentration of an element in a compound or a component in a mixture.
Mass percentage is calculated as the mass of a component divided by the total mass of the mixture, multiplied by 100%.
23. Mole fraction :-It is the ratio of number of moles of a particular component to the total number of moles of the solution.
Mole fraction of A
= (No. of moles of A)/(No. of moles of solution)
(nA )/( nA + nB)
Mole fraction of B
=(No. of moles of B)/(No. of moles of solution)
(nB )/( nA + nB)
24. Molarity :-Molarity is defined as the number of moles of the solute in 1 litre of the solution.
It is widely used unit and is denoted by ‘M’.
Molarity (M) = (No. of moles in solute)/(Volume of solution in litres)
25. Molality:-It is defined as the number of moles of solute present in 1 kg of solvent.
It is denoted by m.
Thus Molality(m) =
(No. of moles of solute)/(Mass of solvent in kg)
26. % composition:-The percentage composition of a given compound is defined as the ratio of the amount of each element to the total amount of individual elements present in the compound multiplied by 100
27. Empirical formula:-An empirical formula represents the simplest whole number ratio of various atoms present in a compound.
Write advantages of Chemistry and mention two problems that is still challenge to scientists.
Chemistry plays a central role in our life some advantages are listed below:-
Advantages of studying chemistry
With a better understanding of chemical principles it has now become possible to design and synthesise new materials having specific magnetic, electric and optical properties.
Safer alternatives to environmentally hazardous refrigerants like CFCs (chlorofluorocarbons), responsible for ozone depletion in the stratosphere, have been successfully synthesised.
Problems which can be tackled with the study of chemistry:-
Management of Green House gases like methane, carbon dioxide etc.
Understanding of bio-chemical processes, use of enzymes for large-scale production of chemicals and synthesis of new exotic materials are some of the intellectual challenges for the future generation of chemists.
Understanding of bio-chemical processes, use of enzymes for large-scale production of chemicals.
Write drugs for treatment of
1. Cancer
2. AIDS
Ans:- 1. Cis-platin and taxol
2. AZT (Azidotgymidine)
Define matter and it's physical states.
Anything that has mass and occupies space is defined as matter.
For example:-soap, notebook, pencil, apple, battery etc.
Physical States of matter
Matter can exist in 3 physical states namely solid, liquid and gas.
Solids
In case of solids, the constituent particles are held very close to each other in an orderly fashion and there is not much freedom of movement.
Solids have definite shape and definite volume.
For example: - Apple it has definite shape as well as definite volume.
Liquids
In liquids, the particles are close to each other but they can move around.
Liquids have definite volume but not definite shape. They take the shape of the container in which they are placed.
For example: Water it takes the shape of the tumbler in which it is poured but has volume.
Gases
In gases, the particles are far apart as compared to those present in solid or liquid states and their movement is easy and fast.
It takes the shape of container in which they are placed.
For example: - Smoke does not have definite shape or volume.
Define 5 laws of chemical combination.
The combination of elements to form compounds is governed by the following five basic laws:-
Law of Conservation of Mass.
Law of Definite Proportions.
Law of Multiple Proportions.
Gay Lussac’s Law of Gaseous Volumes.
Avogadro Law.
Law of Conservation of Mass
Law of conservation of mass states that the matter cannot be created nor be destroyed.
This law was put forth by Antoine Lavoisier in 1789.
He performed careful experimental studies for combustion reactions for reaching to the above conclusion.
Law of Multiple Proportions
According to this law, if two elements can combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element, are in the ratio of small whole numbers.
For example: - Hydrogen combines with oxygen to form 2 compounds, water and hydrogen peroxide.
H2(2g) + (1/2)O2 (16g) -- >H2O(18g)
H2(2g) + O2 (32g) -- > H2O2 (34g)
The masses of oxygen O (16g and 32g) combine with the fixed mass of (2g) hydrogen H. Therefore the simple ratio is 16:32 or 1:2.
This law was given by Dalton in 1803.
Law of Definite Proportions
According to this law, a given compound always contains exactly the same proportion of elements by weight.
This law was given by French chemist, Joseph Proust in 1806.
Gay Lussac’s Law of Gaseous Volumes
Gay Lussac’s law was given by Gay Lussac in 1808.
He observed that when gases combine or are produced in a chemical reaction they do so in a simple ratio by volume provided all gases are at same temperature and pressure.
For example: -
H (Hydrogen) (100mL) + O (Oxygen) (50mL) -- >Water(100mL).
The volumes of hydrogen (H) and oxygen (O) which combine together (i.e. 100mL and 50mL) bear a simple ratio of 2:1.
Avogadro Law
In 1811, Avogadro proposed that equal volumes of gases at the same temperature and pressure should contain equal number of molecules.
He made distinction between atoms and molecules
Write Dalton's atomic theory.
Matter consists of indivisible atoms.
All the atoms of a given element have identical properties including identical mass. Atoms of different elements differ in mass.
Compounds are formed when atoms of different elements combine in a fixed ratio.
Chemical reactions involve reorganisation of atoms. These are neither created nor destroyed in a chemical reaction.
