Chemistry 9th Chap 6 : Topic 6 - Maryam Publications

Chemistry Chapter 6 : Topic 6

Mole Calculations

1 / 20

A student is given two samples: 12 g of carbon and 32 g of oxygen gas. Which statement best explains why both samples contain the same number of particles?

A) Both samples occupy equal volumes at room temperature

B) The masses are proportional to their atomic masses

C) Each sample contains one mole of particles according to their molar masses

D) Oxygen molecules are lighter than carbon atoms

2 / 20

When 44 g of carbon dioxide (CO₂) is taken, which of the following correctly represents the number of moles and molecules?

A) 0.5 mole, 3.01×10²³ molecules

B) 2 moles, 1.204×10²⁴ molecules

C) 1 mole, 6.02×10²³ molecules

D) 44 moles, 6.02×10²³ molecules

3 / 20

A compound has a molar mass of 18 g / mol. If 36 g of this substance is taken, how many moles and molecules are present?

A) 2 moles, 1.204×10²⁴ molecules

B) 0.5 mole, 3.01×10²³ molecules

C) 1 mole, 6.02×10²³ molecules

D) 18 moles, 6.02×10²³ molecules

4 / 20

Which statement best explains why molar mass is essential in converting between mass and number of particles?

A) It relates mass to number of moles, which links to particles

B) It provides the density of a substance

C) It determines the volume of gases only

D) It shows the physical state of matter

5 / 20

A sample contains 3.01×10²³ molecules of methane (CH₄). What is its mass?

A) 8 g

B) 16 g

C) 2 g

D) 4 g

6 / 20

If 24 g of magnesium (Mg) is taken (atomic mass = 24 g / mol), how many atoms are present?

A) 24×6.02×10²³

B) 3.01×10²³

C) 6.02×10²³

D) 1.204×10²⁴

7 / 20

A chemist calculates the molar mass of a compound as 58.5 g/mol. Which substance is most likely this compound?

A) H₂O

B) NH₃

C) NaCl

D) CO₂

8 / 20

If 0.25 mole of a substance has a mass of 10 g , what is its molar mass?

A) 40 g∙mol⁻¹

B) 20 g∙mol⁻¹

C) 80 g∙mol⁻¹

D) 2.5 g∙mol⁻¹

9 / 20

Which statement correctly compares 1 mole of hydrogen gas (H₂) and 1 mole of helium gas (He)?

A) Both contain the same number of atoms

B) Both have the same mass

C) Both contain the same number of particles

D) Hydrogen has more molecules than helium

10 / 20

A sample of oxygen gas contains 12.04×10²³ atoms. How many moles of O₂ molecules are present?

A) 1 mole

B) 2 moles

C) 4 moles

D) 0.5 mole

11 / 20

Which situation correctly demonstrates the application of relative molecular mass?

A) Determining molar mass from atomic masses

B) Measuring temperature change

C) Finding density of solids

D) Calculating number of particles from volume

12 / 20

If a substance has double the molar mass of another, what can be said about equal masses of both substances?

A) They contain equal moles

B) The heavier molar mass substance has more moles

C) Both contain equal particles

D) The heavier molar mass substance has fewer moles

13 / 20

A 28 g sample of nitrogen gas (N₂) contains:

A) 1 mole of atoms

B) 1 mole of molecules

C) 2 moles of atoms

D) Both B and C

14 / 20

Which of the following best explains why mole is called a “counting unit”?

A) It measures volume of gases

B) It measures mass only

C) It determines chemical properties

D) It represents a fixed number of particles

15 / 20

A substance contains 6.02×10²² particles. What fraction of a mole is this?

A) 1

B) 0.1

C) 0.01

D) 10

16 / 20

Which step is essential when converting mass of a compound to number of molecules?

A) Directly divide by atomic number

B) Multiply by density

C) Divide by volume

D) Convert mass to moles, then multiply by Avogadro’s number

17 / 20

If 2 moles of CO₂ are decomposed, how many oxygen atoms are present?

A) 1 mole

B) 2 moles

C) 6 moles

D) 4 moles

18 / 20

Why does 1 mole of NaCl contain more ions than 1 mole of Na atoms?

A) Sodium atoms are heavier

B) NaCl occupies more volume

C) NaCl has higher density

D) NaCl dissociates into two ions

19 / 20

A sample contains 0.5 mole of H₂O. How many hydrogen atoms are present?

A) 3 moles

B) 1 mole

C) 0.5 mole

D) 2 moles

20 / 20

Which reasoning best explains the importance of molar mass in chemical calculations?

A) It defines chemical reactivity

B) It allows comparison between masses and particle numbers

C) It measures energy content

D) It determines boiling point

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