NEET Some Basic Concepts Of Chemistry — Set 1

Question 1

How many significant figures are present in the result of $ 0.0821 \times \frac{300.15}{1.01325} $?

Accepted Answer

0.0821 (3 sig figs), 300.15 (5 sig figs), 1.01325 (6 sig figs). Result ≈ 24.346; limited to 3 sig figs (24.3).

Question 2

How many grams of $ \ce{CaCO3} $ are required to produce 2.24 L of $ \ce{CO2} $ at STP with excess $ \ce{HCl} $? (Molar mass: $ \ce{CaCO3} $ = 100 g/mol)

Accepted Answer

Reaction: $ \ce{CaCO3 + 2HCl -> CaCl2 + CO2 + H2O} $. Moles of $ \ce{CO2} $ = $ \frac{2.24}{22.4} $ = 0.1 mol. 1 mol $ \ce{CO2} $ from 1 mol $ \ce{CaCO3} $; mass = 0.1 × 100 = 10 g.

Question 3

A welding gas (C and H only) produces 3.38 g $ \ce{CO2} $ and 0.69 g $ \ce{H2O} $ on burning. What is its empirical formula? (Atomic masses: C = 12, H = 1, O = 16)

Accepted Answer

Mass of C = $ \frac{12}{44} $ × 3.38 ≈ 0.922 g. Mass of H = $ \frac{2}{18} $ × 0.69 ≈ 0.077 g. Moles: C = $ \frac{0.922}{12} $ ≈ 0.077, H = $ \frac{0.077}{1} $ ≈ 0.077. Ratio = 1 : 1; empirical formula = $ \ce{CH} $.

NEET Chemistry: Some Basic Concepts Of Chemistry — Practice Set 1

Q1. How many significant figures are present in the result of \( 0.0821 \times \frac{300.15}{1.01325} \)?

Q2. How many grams of \( \ce{CaCO3} \) are required to produce 2.24 L of \( \ce{CO2} \) at STP with excess \( \ce{HCl} \)? (Molar mass: \( \ce{CaCO3} \) = 100 g/mol)

Q3. A welding gas (C and H only) produces 3.38 g \( \ce{CO2} \) and 0.69 g \( \ce{H2O} \) on burning. What is its empirical formula? (Atomic masses: C = 12, H = 1, O = 16)

Q4. What is the mass of \( \ce{H2O} \) produced when 8 g of \( \ce{H2} \) reacts with 32 g of \( \ce{O2} \)? (Atomic masses: H = 1, O = 16)

Q5. A solution of \( \ce{HNO3} \) has a molarity of 0.8 M and a density of 1.03 g/mL. What is its molality? (Molar mass: \( \ce{HNO3} \) = 63 g/mol)

Q6. How many grams of \( \ce{Na2SO4} \) are produced when 14.2 g of \( \ce{NaOH} \) reacts with excess \( \ce{H2SO4} \)? (Molar masses: \( \ce{NaOH} \) = 40 g/mol, \( \ce{Na2SO4} \) = 142 g/mol)

Q7. A mixture of 12 g \( \ce{C} \) and 48 g \( \ce{O2} \) is ignited to form \( \ce{CO2} \). What is the mass of \( \ce{CO2} \) produced? (Atomic masses: C = 12, O = 16)

Q8. A 1.5 L sample of a gas at STP weighs 2.1 g and contains only carbon and hydrogen. If it produces 3.52 g of \( \ce{CO2} \) on burning, what is its molecular formula? (Atomic masses: C = 12, H = 1)

Q9. A solution contains 5 ppm of \( \ce{NaCl} \) by mass in water. What is its molality? (Molar mass: \( \ce{NaCl} \) = 58.5 g/mol)

Q10. A solution contains 15 ppm of \( \ce{CaCl2} \) by mass in water. What is its molality? (Molar mass: \( \ce{CaCl2} \) = 111 g/mol)