Calculating Molar Mass Grade 9a
How is the molar mass of a substance determined?
Questions and Answers
- 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
Correct Answer
B. 12.01 g/molExplanation
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/molRate this question:
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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
Correct Answer
C. 16.05 g/molExplanation
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/molRate this question:
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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
Correct Answer
A. 96.11 g/molExplanation
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/molRate this question:
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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
Correct Answer
B. 380.59 g/molExplanation
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/molRate this question:
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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
Correct Answer
A. 213.01 g/molExplanation
(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/molRate this question:
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Mar 17, 2023Quiz Edited by
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Feb 10, 2015Quiz Created by
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