# Calculating Molar Mass Grade 9a

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How is the molar mass of a substance determined?

• 1.

### What is the molar mass of Carbon?

• A.

6 g/mol

• B.

12.01 g/mol

• C.

19.00 g/mol

• D.

1.01 g/mol

B. 12.01 g/mol
Explanation
The molar mass of a substance is determined by the average atomic mass according to the periodic table. The molar mass of carbon is 12.01 g/mol

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• 2.

### What is the molar mass of CH4 (methane)?

• A.

12.01 g/mol

• B.

13.02 g/mol

• C.

16.05 g/mol

• D.

32.10 g/mol

C. 16.05 g/mol
Explanation
The molar mass of a substance is determined by the average atomic mass according to the periodic table. There is 1 carbon in CH4 (methane) and 4 hydrogen:
Carbon 1 (12.01) + Hydrogen 4(1.01) = 16.05 g/mol

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• 3.

### What is the molar mass of (NH4)2CO3 (Ammonium carbonate)?

• A.

96.11 g/mol

• B.

82.10 g/mol

• C.

106.11 g/mol

• D.

43.01 g/mol

A. 96.11 g/mol
Explanation
Molar mass is the mass of one mole of the substance. The molar mass of a substance is determined by the average atomic mass according to the periodic table. CAUTION: The parentheses indicates that everything within the parentheses is MULTIPLIED by the subscript outside of the parentheses. This means there are 2 nitrogen, 8 hydrogen (4 x 2), 1 carbon and 3 oxygen in this compound.
Nitrogen 2(14.01) + Hydrogen 8 (1.01) + Carbon 1 (12.01) + Oxygen 3(16.00) = 96.11 g/mol

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• 4.

### What is the molecular mass of Cu3(PO4)2?

• A.

253.49 g/mol

• B.

380.59 g/mol

• C.

110.22 g/mol

• D.

348.59 g/mol

B. 380.59 g/mol
Explanation
Molar mass is the mass of ONE mole of a substance regardless of how many moles there are in the equation. CAUTION: The parentheses indicates that everything within the parentheses is MULTIPLIED by the subscript outside of the parentheses.
This means there are 3 Coppers, 2 Phosphorus, 8 oxygen:
Copper 3 (63.55) + Phosphorus 2(30.97) + 8 (16.00) = 380.59 g/mol

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• 5.

### What is the molecular mass of Aluminum nitrate Al(NO3)3 from this equation: 2Al(s)   + 3Fe(NO3)2(aq)   à 3Fe(s)  + 2Al(NO3)3(aq)

• A.

213.01 g/mol

• B.

335.98 g/mol

• C.

56.99 g/mol

• D.

141.01 g/mol

A. 213.01 g/mol
Explanation
(s) means solid and (aq) means aqueous.
Molar mass is the mass of ONE mole of a substance regardless of how many moles there are in the equation. So, ignore the “2” in front of Al(NO3)3
CAUTION: The parentheses indicates that everything within the parentheses is MULTIPLIED by the subscript outside of the parentheses.
This means there is 1 Aluminum, 3 Nitrogen, 9 oxygen (3 x 3)
The molar mass of a substance is determined by the average atomic mass according to the periodic table.
Aluminum 1 (26.98) + Nitrogen 3 (14.01) + Oxygen 9 (16.00) = 213.01 g/mol

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