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) The masses are proportional to their atomic masses

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

C) Oxygen molecules are lighter than carbon atoms

D) Both samples occupy equal volumes at room temperature

2 / 20

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

A) 1 mole, 6.02×10²³ molecules

B) 2 moles, 1.204×10²⁴ molecules

C) 0.5 mole, 3.01×10²³ 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) 1 mole, 6.02×10²³ molecules

C) 0.5 mole, 3.01×10²³ 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 shows the physical state of matter

B) It provides the density of a substance

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

D) It determines the volume of gases only

5 / 20

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

A) 16 g

B) 2 g

C) 8 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) 1.204×10²⁴

B) 6.02×10²³

C) 3.01×10²³

D) 24×6.02×10²³

7 / 20

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

A) NaCl

B) H₂O

C) CO₂

D) NH₃

8 / 20

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

A) 20 g∙mol⁻¹

B) 2.5 g∙mol⁻¹

C) 40 g∙mol⁻¹

D) 80 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 particles

B) Both have the same mass

C) Hydrogen has more molecules than helium

D) Both contain the same number of atoms

10 / 20

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

A) 0.5 mole

B) 2 moles

C) 4 moles

D) 1 mole

11 / 20

Which situation correctly demonstrates the application of relative molecular mass?

A) Calculating number of particles from volume

B) Measuring temperature change

C) Determining molar mass from atomic masses

D) Finding density of solids

12 / 20

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

A) The heavier molar mass substance has fewer moles

B) Both contain equal particles

C) The heavier molar mass substance has more moles

D) They contain equal moles

13 / 20

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

A) 1 mole of atoms

B) 2 moles of atoms

C) 1 mole of molecules

D) Both B and C

14 / 20

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

A) It determines chemical properties

B) It represents a fixed number of particles

C) It measures volume of gases

D) It measures mass only

15 / 20

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

A) 1

B) 0.01

C) 10

D) 0.1

16 / 20

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

A) Divide by volume

B) Directly divide by atomic number

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

D) Multiply by density

17 / 20

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

A) 6 moles

B) 1 mole

C) 2 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 has higher density

C) NaCl occupies more volume

D) NaCl dissociates into two ions

19 / 20

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

A) 0.5 mole

B) 1 mole

C) 3 moles

D) 2 moles

20 / 20

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

A) It allows comparison between masses and particle numbers

B) It defines chemical reactivity

C) It determines boiling point

D) It measures energy content

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