Question:
Calculate the number of molecules of phosphorus (P4) present in 31 gram of phosphorus.
Answer:
Atomic mass of phosphorus = 31 u
Molecular mass of P4 = 31× 4 = 124 u
⇒ Molar mass of P4 = 124 g/mol.
⇒ Mass of 1 mole ( 6.023 × 1023 ) P4 molecules = 124 g
∴ 124 g of P4 = 6.023 × 1023 molecules of P4
1g of P4 = ( 6.023 × 1023 )/(124) = 0.25 × 1023 molecules
31g P4 = 0.25 × 1023 × 31 = 1.5 × 1023 molecules .... answer
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, CH
Q 9.
Calculate the molecular masses of the following compounds :
(a) Hydrogen sulphide, H2S
(b) Carbon disulphide, CS
2
(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) CuSO
4
(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 (CaCO
3) 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 (S
8) 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,HNO
3.
(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)Al
2O3(ii) co
2(iii) C1
2O7 (iv) H
2SO4(p)A1
2(S04)3
Q 32.
What is the law of conservation of mass?
Q 33.
State Law of constant proportions. Explain with an example.
Q 34.
Which postulate of Dalton’s atomic theory can explain the law of definite proportions?
Q 35.
Name the international organization who approves names of elements.
Q 36.
Which element has the smallest atom in size?
Q 37.
Fill in the blanks:
The atomicity of sulphur S
8 is ________.
Q 38.
Fill in the blanks:
One mole of water contains ______________ molecules.
Q 39.
Give the names of the elements present in the following compounds.
(a) Quick lime
(b) Hydrogen bromide
(c) Baking powder
(d) Potassium sulphate.
Q 40.
Name one element which forms diatomic and triatomic molecule.
Q 41.
Define mole. What is its significance?
Q 42.
What is molar mass?
Q 43.
Find out number of atoms in 15 moles of He.
Q 44.
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 45.
Calculate the mass percentage of Carbon(C) , Hydrogen (H) and Oxygen (O) in one molecule of glucouse (C
6H
12O
6).
(Atomic mass of C = 12u, H = 1u and O = 16u)
Q 46.
What are the building blocks of matter ?
Q 47.
Dalton's atomic theory says that atoms are indivisible. Is this statement still valid ? Give reasons for answer.
Q 48.
Calculate the molecular mass of ethanoic acid, CH
3COOH.
(Atomic masses :C = 12u;H = lu;0 = 16u)
Q 49.
Calculate the molecular mass of chloroform (CHC1
3).
(Atomic masses :C= 12u;H = lu;Cl = 35.5u)
Q 50.
State whether the following statements are true or false :
(a)A sodium ion has positive charge because it has more protons than a neutral atom
(b)A chloride ion has negative charge because it has more electrons than a neutral atom.