BASIC CONCEPTS OF CHEMISTRY
Q.1 Choose the correct option
1. A sample of pure water, whatever the source always contains 88.8.by mass of oxygen and 11.1% by mass of hydrogen.
Q.1 Choose the correct option
1. A sample of pure water, whatever the source always contains 88.8.by mass of oxygen and 11.1% by mass of hydrogen.
2. Which of the following compounds cannot demonstrate the law of multiple proportions? = NaS, NaF
3. Which of the following temperature will read the same value on Celsius and Fahrenheit scales. = -40
4. Sl unit of the quantity electric current is Ampere.
5. In the reaction N2 + 3H2
2NHg, the ratio by volume of N2, H2 and NH3 is 1 : 3 : 2 This illustrates the
law of gaseous volumes
6. Which of the following has maximum number of molecules? =2gH2
7. How many g of H20 are present in 0.25 mol of it? = 4.5
8. The number of molecules in
22.4 cm3 of nitrogen gas at STP is 16.022 x 1020
9. Which of the following has maximum number of molecules? = 1g Li(s)
Q.2 Answer the following question
(1) State and explain Avogadro's law
i) In the year 1811, Avogadro made a distinction between atoms and molecules and here by proposed Avogadro's law.
ii) Avogadro proposed that, "Equal volumes of all gases at the same temperature and pressure contain an equal number of molecules".
e.g. Hydrogen gas combines with oxygen gas to produce water vapour as follows:
Hydrogen(g) + Oxygen(g) —+ Water (g)
According to Avogadro's law, if 1 volume contains n molecules, then 2n molecules of hydrogen combine with n molecules of
oxygen to give 2n molecules of water, i.e., 2 molecules of hydrogen gas combine with 1 molecule of oxygen to give 2
molecules of water vapour as represented below:
Hydrogen (g) + Oxygen (g) —+ Water (g)
2. Point out the difference between 12 g of carbon and 12 u of carbon. ?
Answer- 12 of carbon is the molar mass of carbon while 12 u of carbon is the mass of one carbon atom.
Answer- The mass of a hydrogen atom is 1.6736 x 10 24 g.
4. Calculate the molecular mass of the following in u.
(A) NH3
Answer-Molecular mass of NH3 = (1 x Average atomic mass of N) + (3 x Average atomic mass of H)
=(1 x 14.0u) + (3 x 1.0 u)
=(1 x 14.0u) + (3 x 1.0 u)
=-17 u
The molecular mass of NH3 = 17 u
(B) CH3COOH
=(2 x 12.0 u) + (4x 1.0 u) + (2 x 16.0 u)
=60 u
The molecular mass of CH3COOH = 60 u
(c) C2H50H
Molecular mass of C2HsOH = (2 x Average atomic mass of C) + (6 x Average atomic mass of H) + (1 x Average atomic mass of O)
=(2 x 12.0 u) + (6 x 1.0 u) + (1 x 16.0 u)
=46
(5) How many particles are present in 1 mole of a substance?
Answer- The number of particles in one mole is 6.0221367 x 10
(6) What is the SI unit of the amount of a substance?
Answer- The Sl unit for the amount of a substance is mole (mol).
(7) What is meant by the molar volume of a gas?
Answer- The volume occupied by one mole of a gas at standard temperature (OOC) and pressure (1 atm) (STP) is called a molar volume of a gas. The
(1 atm) (STP) is called a molar volume of a gas. The molar volume of a gas at STP is 22.4 dm3.
(8) State and explain the law of conservation of mass.
Answer- Law of conservation of mass:
i) The law of conservation of mass states that "Mass can neither be created nor destroyed" during the chemical combinations of matter.
ii) Antoine Lavoisier who is often referred to as the father of modern chemistry
performed careful experimental studies for various combustion reactions, namely burning of phosphorus and mercury in the presence of air.
iii) 80th his experiments resulted in an increased weight of products.
iv) After several experiments, in the burning of phosphorus, he found that the weight
gained by the phosphorus was exactly the same as the weight lost by the air. Hence, the total mass of reactants = total mass of products.
v) When hydrogen gas burns and combines with oxygen to form water, the mass of the
water formed is equal to the mass of the hydrogen and oxygen consumed. Thus, this is in accordance with the law of conservation of mass.
(9) State the law of multiple proportions.
Answer- The law states that "When two elements A and B form more than one compounds, the masses of element B that combine with a
given mass of A are always in the ratio of small whole numbers".
Q.3 Give one example
of each
(1) Homogeneous mixture.
Answer- Homogeneous mixture: Solution (An aqueous solution of sugar)
(2) Heterogeneous mixture.
Answer-Heterogeneous mixture: Suspension (of sand in water)
(3) Element.
Answer-Gold
*NOTES OF SOME BASIC CONCEPTS OF CHEMISTRY*
• Matter
Anything which has mass and occupies space is called matter.
For example, book, pencil, water, air are composed of matter as we know that they have
mass and they occupy space.
Anything which has mass and occupies space is called matter.
For example, book, pencil, water, air are composed of matter as we know that they have
mass and they occupy space.
• Classification of Matter
There are two ways of classifying the matter:
(A) Physical classification
(B) Chemical classification
There are two ways of classifying the matter:
(A) Physical classification
(B) Chemical classification
(A) Physical Classification:
Matter can exist in three physical states:
1. Solids 2. Liquids 3. Gases
1. Solids: The particles are held very close to each other in an orderly fashion and there is not much freedom of movement.
Characteristics of solids: Solids have definite volume and definite shape.
2. Liquids: In liquids, the particles are close to each other but can move around. Characteristics of liquids: Liquids have definite volume but not definite shape.
3. Gases: In gases, the particles are far apart as compared to those present in solid or liquid states. Their movement is easy and fast.
(B) Chemical Classification:
Based upon the composition, matter can be divided into two main types:
1. Pure Substances 2. Mixtures.
1. Pure substances: A pure substance may be defined as a single substance (or matter) which cannot be separated by simple physical methods.
Pure substances can be further classified as (i) Elements (ii) Compounds
(i) Elements: An element consists of only one type of particles. These particles may be atoms or molecules.
For example, sodium, copper, silver, hydrogen, oxygen etc. are some examples of elements. They all contain atoms of one type. However, atoms of different elements are different in nature. Some elements such as sodium . or copper contain single atoms held together as their constituent particles whereas in some others two or more atoms combine to give molecules of the element. Thus, hydrogen, nitrogen and oxygen gases consist of molecules in which two atoms combine to give the respective molecules of the element
(ii) Compounds: It may be defined as a pure substance containing two or more elements combined together in a fixed proportion by weight and can be decomposed into these elements by suitable chemical methods. Moreover, the properties of a compound are altogether different from the constituting elements.
The compounds have been classified into two types. These are:
(i) Inorganic Compounds: These are compounds which are obtained from non-living sources such as rocks and minerals. A few
examples are: Common salt, marble, gypsum, washing soda etc.
(ii) Organic Compounds are the compounds which are present in plants and animals. All the organic compounds have been found to contain carbon as their essential constituent.
For example, carbohydrates, proteins, oils, fats etc.
(2) Mixtures: The combination of two or more elements or compounds which are not chemically combined together and may also be present in any proportion, is called mixture. A few examples of mixtures are: milk, sea water, petrol, lime water, paint glass, cement, wood etc.
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