Solution
UNIT TEST -1
Class 11 - Chemistry
Section A
1.
(a) 3,1,1,3
Explanation: The given equation gets balanced by inserting the coefficients (3,1,1,3) in blank spaces from LHS to RHS. Thus,
the balanced equation for the given reaction is 3KOH + H3PO4 ⟶ K3PO4 + 3H2O.
2.
(a) meaningful digits which are known with certainty
Explanation: Significant digits are certain digits that have significance or meaning to certain digits in a number. Such digits
help scientists to use them with more precise information about measurement and other numeric data. These digits also help
them in rounding off a very large or very small number
3.
(a)
of the mass of C-12 atom
1
12
Explanation:
4.
1
12
of the mass of C-12 atom
(d) the exact number of different types of atoms present in a molecule of a compound
Explanation: Molecular formula is the exact no. of atoms present in a molecule of a compound.
Molecular formula of a compound is related with its empirical formula as,
Mollecular formula = (Empirical formula)n
where n represents a positive integer.
5.
(b) 4.7g
Explanation: Mass = Density × Volume
= 3.12 g mL-1 × 1.5 mL = 4.68 g = 4.7 g
significant figures as that of the least given number. Therefore, correct answer is 4.7 g
6.
(d) stoichiometry
Explanation: Out of various aspects of studies undertaken to study a chemical change (viz. qualitative, thermodynamic,
kinetics, equilibrium studies, etc.), it becomes essential for chemists to study the quantitative relationship between reacting
substances (known as reactants) and the products ( ie. substances yielded). Such a chemical interaction is termed as a 'chemical
reaction ', &. the quantitative study is known as " Stoichiometry ". It is preferred to carry out stoichiometric calculations in a
balanced chemical equation.
7.
(d) A is false but R is true.
Explanation: A is false but R is true.
8.
(a) Both A and R are true and R is the correct explanation of A.
Explanation: Any substance that contains only one kind of atom is known as an element. They can be broken down into
simpler substances. Two or more elements combine together to form componds.
Section B
9. Molecular mass of Ca3(PO4)2 = 3× Ca + 2(1× P +4 × O ) = 3 × 40 + 2(1 × 31 + 4 × 16)= 310u
Mass percent of calcium=
=
120u
310u
× 100
3×( atomic mass of calcium )
molecular mass of Ca3 (P O4 )
= 38.71%
Mass percent of phosphorus=
=
2×31u
310u
× 100
=
310u
× 100
2×( atomic mass of phosphorus)
molecular mass of Ca3 (P O4 )
× 100
2
= 20%
Mass percent of oxygen =
8×16u
× 100
2
8×(Atomic mass of oxygen)
molecular mass of Ca3 (P O4 ) 2
× 100
= 41.29%
10. i. 6.509
ii. 32.39
iii. 8.721 × 104
iv. 2.000 × 103
Section C
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11. 2N
(g) + O2 (g) → 2N2 O (g)
2
2V
45.4
22.7
=2
1V
22.7
22.7
=1
2V
45.4
=2
22.7
Hence, the ratio between the volume of the reactants and the product in the given question is simple i.e. 2:1:2. It proves the GayLassac's law of gaseous volumes.
Gay Lussac’s Law of Gaseous Volumes (Given by Gay Lussac's in 1808) : According to this law, when gases combine or are
produced in a chemical reaction they do so in a simple ratio by volume, provided all the gases are at same temperature and
pressure.
12. As shown in figure, the masses of H and O which combine with the fixed mass of S, i.e. 32 parts are 2 and 32 i.e. they are in the
ratio 2 : 32 or 1 : 16. When H and O combine directly to form H2O, the ratio of their combining , masses are 2:16 or 1 : 8.
These ratio are related to each other as
1
16
:
1
8
=1:2
i.e. they are simple multiple of each other.
Section D
13. millimoles of HCl = Molarity × Volume (in mL)
where Molarity = 0.75 M , Volume = 25 ml
We know that millimoles of HCl = millimoles of CaCO3
So, millimoles of CaCO3 = 25 mL × 0.75 M of HCl
= 18.75 millimoles = 18.75 × 10-3 moles
From the given reaction it is clear that 2 moles of HCl reacts with 1 mole of CaCO3
C aC O3 + 2HC I (aq) → C aC I2 (aq) + C O2 (g) + H2 O(I )
So 18.75 x 10-3 moles of HCl reacts with
18.75×1
2
×
10-3 moles of CaCO3 = 9.375 × 10-3 moles
mass of CaCO3 required = molar mass of CaCO3 × moles of CaCO3
mass of CaCO3 = 100 g/mol × 9.375 x 10-3 mol = 0.9375 g
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