Grade 11 : Chemistry - Basic Concepts (Set 2) | Concept of Maths

Question 1

1. A jewelry designer measures the mass of a pure gold ring as $19.700\text{ g}$. How many significant figures are present in this measurement?

A) 3

B) 4

C) 5

D) 2

Answer

Correct Answer: C

Explanation: According to the rules for significant figures, trailing zeros in a number containing an explicit decimal point are significant. Therefore, all five digits ($1, 9, 7, 0, 0$) are significant.

Question 2

2. An environmentalist analyzes water samples from a local river and a distant glacier. Both samples show that hydrogen and oxygen are present in a mass ratio of $1:8$. This observation supports which law?

A) Law of Conservation of Mass

B) Law of Definite Proportions

C) Law of Multiple Proportions

D) Gay Lussac's Law of Gaseous Volumes

Answer

Correct Answer: B

Explanation: The Law of Definite Proportions (Proust's Law) states that a given chemical compound always contains its component elements combined together in a fixed, constant ratio by mass, completely independent of its source or method of preparation.

Question 3

3. A chef uses $46\text{ g}$ of sodium (atomic mass $= 23\text{ u}$) in a specialized chemical cooking process. How many moles of sodium atoms did the chef use?

A) $2.0\text{ mol}$

B) $1.0\text{ mol}$

C) $0.5\text{ mol}$

D) $46\text{ mol}$

Answer

Correct Answer: A

Solution: $$\text{Number of moles } (n) = \frac{\text{Given mass } (w)}{\text{Molar mass } (M)}$$ $$n = \frac{46\text{ g}}{23\text{ g/mol}} = 2.0\text{ mol}$$

Question 4

4. A weather balloon is filled with $4.0\text{ g}$ of Helium gas (atomic mass $= 4\text{ u}$). What volume will this gas occupy at STP (Standard Temperature and Pressure)?

A) $11.2\text{ L}$

B) $44.8\text{ L}$

C) $2.24\text{ L}$

D) $22.4\text{ L}$

Answer

Correct Answer: D

Solution: $$\text{Moles of He} = \frac{4.0\text{ g}}{4\text{ g/mol}} = 1\text{ mol}$$ Since $1\text{ mole}$ of any ideal gas occupies precisely $22.4\text{ L}$ volume space at standard conditions (STP), the final value is $22.4\text{ L}$.

Question 5

5. A laboratory produces a cleaning agent by dissolving $40\text{ g}$ of $NaOH$ (molar mass $= 40\text{ g/mol}$) in enough water to make $500\text{ mL}$ of solution. What is the molarity ($M$) of this solution?

A) $1.0\text{ M}$

B) $2.0\text{ M}$

C) $0.5\text{ M}$

D) $4.0\text; M}$

Answer

Correct Answer: B

Solution: $$\text{Moles of NaOH} = \frac{40\text{ g}}{40\text{ g/mol}} = 1\text{ mol}$$ $$\text{Volume in Liters} = \frac{500\text{ mL}}{1000} = 0.5\text{ L}$$ $$\text{Molarity } (M) = \frac{\text{moles of solute}}{\text{Volume of solution in L}} = \frac{1}{0.5} = 2.0\text{ M}$$

Question 6

6. An industrial process requires the reaction of $12\text{ g}$ of Magnesium with $16\text{ g}$ of Oxygen to form Magnesium Oxide ($MgO$). If the Law of Conservation of Mass holds perfectly, what is the expected mass of the product?

A) $4\text{ g}$

B) $24\text{ g}$

C) $28\text{ g}$

D) $56\text{ g}$

Answer

Correct Answer: C

Explanation: According to the Law of Conservation of Mass, the combined mass of the reactants must precisely equal the net total mass of the generated products. $$\text{Total Product Mass} = 12\text{ g (Mg)} + 16\text{ g (O)} = 28\text{ g}.$$

Question 7

7. A molecule used in botanical research has the molecular formula $C_6H_{12}O_6$. What is its empirical formula?

A) $CH_2O$

B) $CHO$

C) $C_2H_4O_2$

D) $CH_3O$

Answer

Correct Answer: A

Solution: The empirical formula tracks the lowest, simplest whole-number ratio of individual atoms inside a compound. Atomic ratio $C:H:O = 6:12:6$. Dividing through by the lowest factor ($6$) gives: $1:2:1$. $$\text{Empirical Formula} = CH_2O.$$

Question 8

8. A scientist finds that $1$ mole of a gas contains approximately $6.022 \times 10^{23}$ molecules. This constant quantitative value is universally known as:

A) Planck's Constant

B) Avogadro's Number

C) Boltzmann Constant

D) Rydberg Constant

Answer

Correct Answer: B

Explanation: The value $6.022 \times 10^{23}$ denotes **Avogadro's Number** ($N_A$). It serves as the standard counting index baseline containing fundamental entities per single mole of a substance.

Question 9

9. In a fertilizer plant, a technician mixes $10\text{ g}$ of urea in $90\text{ g}$ of water. What is the mass percent of urea in the solution?

A) $90\%$

B) $11.1\%$

C) $100\%$

D) $10\%$

Answer

Correct Answer: D

Solution: $$\text{Mass } \% \text{ of solute} = \left( \frac{\text{Mass of solute}}{\text{Mass of solute} + \text{Mass of solvent}} \right) \times 100$$ $$\text{Mass } \% \text{ of urea} = \left( \frac{10}{10 + 90} \right) \times 100 = \left( \frac{10}{100} \right) \times 100 = 10\%.$$

Question 10

10. Which of the following configurations represents a heterogeneous mixture in a real-world setting?

A) A sugar solution in water

B) Filtered air

C) A mixture of sand and iron filings

D) Pure distilled water

Answer

Correct Answer: C

Explanation: A heterogeneous mixture maintains a non-uniform composition throughout its structure where components can be physically distinguished. Sand and iron filings do not intermix uniformly and can be parsed apart easily via common mechanical tools like a magnet.

Grade 11 : Chemistry - Basic Concepts (Set 2) | Concept of Maths