Some Basic Concepts of Chemistry

1.43. The mass of one atom of C-12 in grams is:

(a) 6.022 * 10²³ g

(b) 6.022 * 10²³ kg

(c) 1.99 * 10^–23 g

(d) 1.99 * 10^–23 kg

1.43. The mass of one atom of C-12 in grams is:

(a) 6.022 × 10²³ g

(b) 6.022 × 10²³ kg

(c) 1.99 × 10^–23 g

(d) 1.99 × 10^–23 kg

MCQs

1.42. Which of the following statements is correct? 

(a) 100 has only one significant figure

(b) 100. has three significant figures

(c) 100.0 has four significant figures

(d) all the above

1.41. Assertion: In chemical reactions, the reactant, which gets consumed first, limits the amount of product formed and is called the limiting reagent.

R: Stoichiometry deals with the calculation of masses (sometimes volumes also) of the reactants and the products involved in a chemical reaction.

1.40. Assertion: SI unit of volume is L (litre).

R: But again, in chemistry laboratories, volumes is often denoted in cm³ or dm³ units.

1.39. Assertion: Volume of a gas is inversely proportional to the number of moles of gas.

Reason: The ratio by volume of gaseous reactants and products agrees with their mole ratio.

1.38. Assertion: Volume of a gas is inversely proportional to the number of moles of gas.

Reason: The ratio by volume of gaseous reactants and products agrees with their mole ratio.

1.38. Assertion: 123.00 has three significant figures.

Reason: All numbers right to the decimal point are significant.

Assertion Type Questions:

1.37. Assertion: One mole of any gas contains 6.022 x 10²³ molecules.

Reason: 1 g of any gas contains equal number of moles.

1.36. Chlorine is prepared in the laboratory by treating manganese dioxide (MnO₂) with aqueous hydrochloric acid according to the reaction.

4 HCl (aq) + MnO₂ (s) ———–> 2 H₂O (l) + MnCl₂(aq) +Cl₂(g)

How many grams of HCl react with 5.0 g of manganese dioxide? (Atomic mass of Mn = 55 u