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Some Basic Concepts of Chemistry

Multiple Choice Questions

341.
In acid medium, Zn reduces nitrate ion to NH $_{4}^{+}$ ion according to the reaction,
Zn + NO $_{3}^{-}$ → Zn²⁺ + NH $_{4}^{+}$ + H₂O (unbalanced).
How many moles of HCl are required to reduce half a mole of NaNO₃ completely ? Assume the availability of sufficient Zn.

5

4

3

2

The above given unbalanced equation can be balanced as follows-

(i) Split the reaction in two halves.

Zn → Zn²⁺ ; NO $_{3}^{-}$ → NH $_{4}^{+}$

(ii) Add water molecules to the side deficient in oxygen and H⁺ to the side deficient in hydrogen.

Zn → Zn²⁺ ; NO $_{3}^{-}$ + 10 H⁺ → NH $_{4}^{+}$ + 3H₂O

(iii) The number of electrons are balanced and then add the two half equations.

[Zn → Zn²⁺ + 2e^-] × 4;

NO $_{3}^{-}$ + 10H⁺ + 8e^- → NH $_{4}^{+}$ + 3H₂O

4Zn → 4Zn²⁺ + 8e^-

$∴$ 4Zn + NO $_{3}^{-}$ + 10 HCl → 4Zn²⁺ + NH $_{4}^{+}$ + 3H₂O

or 4Zn + NO $_{3}^{-}$ + 10HCl → 4Zn²⁺ + NH $_{4}^{+}$ + 5Cl₂ + 3H₂O

$∵$ 1 mole of NO $_{3}^{-}$ (or NaNO₃) is reduced by = 10 moles of HCl

$∴ \frac{1}{2}$ mole of NO $_{3}^{-}$ will be reduced by = 10 × $\frac{1}{2}$ moles of HCl

= 5 moles of HCl

342.

The percentage of an element M is 53 in its oxide of molecular formula M₂O₃. Its atomic mass is about

343.

The relative lowering of vapour pressure of a dilute aqueous solution containing non-volatile solute is 0.0125. The molality of the solution is about

0.70
0.50
0.90
0.80

344.

The pH of a solution obtained by mixing 50 mL of 1 N HCl and 30 mL of 1 N NaOH is [log 2.5 = 0.3979]

12.042
0.6021
0.3979
3.979

345.

0.1 mole of a carbohydrate with empirical formula CH₂O contains 1 g of hydrogen. What is its molecular formula?

C₂H₄O₂
C₅H₁₀O₅
C₃H₆O₃
C₆H₁₂O₆

346.

How much of sulphur is present in an organic compound, if 0.53 g of the compound gave 1.158 g of BaSO₄ on analysis ?

347.

Commercial 11.2 volume H₂O₂ solution has a molarity of :

1.0
0.5
11.2
1.12

348.

100 g CaCO₃ is treated with 1 L of 1N HCl. What would be the weight of CO₂ liberated after the completion of the reaction ?

55 g
11 g
22 g
33 g

349.

Law of multiple proportions is illustrated by one of the following pairs :

N₂O and NO
H₂S and SO₂
NH₃ and Na₂O
BeO and BeCl₂

350.

Avogadro's hypothesis states that :

the ideal gas consists of a large number of small particles called molecules
under the same conditions of temperature and pressure equal volumes of gases contain the same number of molecules
volume of a definite quantity of gas at constant pressure is directly proportional to absolute temperature
a given mass of gas at constant pressure is directly proportional to absolute temperature

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Multiple Choice Questions

341. In acid medium, Zn reduces nitrate ion to NH4+ ion according to the reaction,Zn + NO3-→ Zn2+ + NH4+ + H2O (unbalanced).How many moles of HCl are required to reduce half a mole of NaNO3 completely ? Assume the availability of sufficient Zn. 5 4 3 2

341.
In acid medium, Zn reduces nitrate ion to NH $_{4}^{+}$ ion according to the reaction,
Zn + NO $_{3}^{-}$ → Zn²⁺ + NH $_{4}^{+}$ + H₂O (unbalanced).
How many moles of HCl are required to reduce half a mole of NaNO₃ completely ? Assume the availability of sufficient Zn.

5

4

3

2