Chemistry

Atoms and Molecules

Question:

Give an example to show Law of conservation of mass applies to physical change also.

Answer:

When ice melts into water, is a physical change. Take a piece of ice in small flask, cork it and weight it (say Wice gm). Heat the flask gently and ice (solid) slowly melts into water (liquid). Weigh the flask again (Wwater gm). It is found there is no change in the weight i.e. Wice= Wwater.
                              Heat(Δ)
                        Ice  ----------➜   Water
This shows law of conservation of mass holds true for physical changes.
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Atoms and Molecules

Q 1.

How many moles are there in 4.6 gms of Sodium(Na)?

Q 2.

What is the mass of:
(a) 0.2 mole of oxygen atoms?
(b) 0.5 mole of water molecules?

Q 3.

What is the numerical value of Avogadro number ?

Q 4.

Name the unit in which the radius of an atom is usually expressed.

Q 5.

Fill in the blanks:
According to law of definite proportions, in a chemical substance the elements are always present in __________ proportions by mass.

Q 6.

Fill in the blanks:
According to Dalton's atomic theory, atoms of different elements differ in ______, size and chemical properties.

Q 7.

Write the full form of IUPAC.

Q 8.

Calculate the molecular masses of the following compounds :
(a) Methanol, CH3OH
(b) Ethanol, C2H5OH

Q 9.

Calculate the molecular masses of the following compounds :
(a) Hydrogen sulphide, H2S
(b) Carbon disulphide, CS2
(Atomic masses :H = lu;S = 32u;C = 12u)

Q 10.

An element Z has a valency of 3. What is the formula of oxide of Z ?

Q 11.

Name the following compounds. Also write the symbols/formulae of the ions present in them :
(a) CuSO4
(b) (NH4)2SO4
(c)Na2O
(d)Na2CO3
(e)CaCl2

Q 12.

How many moles are 3.6 g of water ?

Q 13.

How many moles of calcium carbonate (CaCO3) are are present in 10 g of the substance ? (Ca = 40 u • C= 12 u-O = 16 u)

Q 14.

If one mole of nitrogen molecules weighs 28 g, calculate mass of one molecule of nitrogen in grams.

Q 15.

Which postulate of Dalton’s atomic theory is the result of the law of conservation of mass?

Q 16.

What is relative atomic mass of an element? How it is related to atomic mass unit?

Q 17.

Give four examples of diatomic molecules.

Q 18.

An element X has a valency of 4 whereas another element Y has a valency of 1. What will be the formula of the compound formed between X and Y ?

Q 19.

What is an ion ? How is an ion formed ? Explain with the help of two examples of different ions.

Q 20.

(a) Define gram molecular mass of a substance. How much is the gram molecular mass of oxygen ?
(b) If sulphur exists as S8 molecules, calculate the number of moles in 100 g of sulphur.. (S = 32 u)

Q 21.

Is there any exception to law of conservation of mass?

Q 22.

Give examples of triatomic molecules.

Q 23.

Name one element each which forms diatomic and tetra atomic molecule.

Q 24.

Calculate the number of molecules of sulphur (S8) present in 16 g of solid sulphur.

Q 25.

What is meant by atomicity ? Explain with two

Q 26.

Calculate the molecular mass of nitric acid,HNO3.
(Atomic masses :H =lu; N = 14u;0 = 16u)

Q 27.

What do we call those particles which are formed :
(a)by the gain of electrons by atoms ?
(b)by the loss of electrons by atoms ?

Q 28.

What is the difference between a cation and an anion ? Explain with examples. Using this information, write down the formulae of:
(i) Sodium sulphide
(ii) Copper nitrate

Q 29.

Fill in the following blanks :
(a)1 mole Contains...........atoms- molecules or ions of a substance
(b)A mole represents an..........number of Particles of a substance.
(c)60 g of carbon element are...........moles of carbon atoms.
(d) 0.5 mole of calcium element has a mass of..........
(e) 64 g of oxygen gas contains..........moles of oxygen atoms.

Q 30.

Calculate the number of molecules in 4 g of oxygen.

Q 31.

(a) Define gram atomic mass of a substance.How much is the gram atomic mass of oxygen ?
(b) How many moles of oxygen atoms are present in one mole of the following compounds ?
(i)Al2O3(ii) co2(iii) C12O7 (iv) H2SO4(p)A12(S04)3

Q 32.

What is the law of conservation of mass?

Q 33.

Explain with example that law of conservation of mass is valid for chemical reactions.

Q 34.

State Law of constant proportions. Explain with an example.

Q 35.

Which postulate of Dalton’s atomic theory can explain the law of definite proportions?

Q 36.

Name the international organization who approves names of elements.

Q 37.

Which element has the smallest atom in size?

Q 38.

Fill in the blanks:
The atomicity of sulphur S8 is ________.

Q 39.

Fill in the blanks:
One mole of water contains ______________ molecules.

Q 40.

Give the names of the elements present in the following compounds.
(a) Quick lime
(b) Hydrogen bromide
(c) Baking powder
(d) Potassium sulphate.

Q 41.

Name one element which forms diatomic and triatomic molecule.

Q 42.

Define mole. What is its significance?

Q 43.

What is molar mass?

Q 44.

Find out number of atoms in 15 moles of He.

Q 45.

Calculate the number of aluminium ions present in 0.051 g of aluminium oxide.
(Hint: The mass of an ion is the same as that of an atom of the same element. Atomic mass of Al = 27 u)

Q 46.

Calculate the mass percentage of Carbon(C) , Hydrogen (H) and Oxygen (O) in one molecule of glucouse (C6H12O6).
(Atomic mass of C = 12u, H = 1u and O = 16u)

Q 47.

What are the building blocks of matter ?

Q 48.

Dalton's atomic theory says that atoms are indivisible. Is this statement still valid ? Give reasons for answer.

Q 49.

Calculate the molecular mass of ethanoic acid, CH3COOH.
(Atomic masses :C = 12u;H = lu;0 = 16u)

Q 50.

Calculate the molecular mass of chloroform (CHC13).
(Atomic masses :C= 12u;H = lu;Cl = 35.5u)