Mole to Grams, Grams to Moles Conversions Worksheet for chemistry practice.

Here are the solutions to the problems on the worksheet. I have solved all of them so you can check your work.

Part 1: Molecular Weights

To find the molecular weight, we add up the atomic masses of all the atoms in the formula. (Atomic masses are rounded to two decimal places).

1) NaOH
* Na: 22.99
* O: 16.00
* H: 1.01
* Total: $22.99 + 16.00 + 1.01 = \mathbf{40.00 \text{ g/mol}}$

2) H₃PO₄
* H: $1.01 \times 3 = 3.03$
* P: 30.97
* O: $16.00 \times 4 = 64.00$
* Total: $3.03 + 30.97 + 64.00 = \mathbf{98.00 \text{ g/mol}}$

3) H₂O
* H: $1.01 \times 2 = 2.02$
* O: 16.00
* Total: $2.02 + 16.00 = \mathbf{18.02 \text{ g/mol}}$

4) Mn₂Se₇
* Mn: $54.94 \times 2 = 109.88$
* Se: $78.97 \times 7 = 552.79$
* Total: $109.88 + 552.79 = \mathbf{662.67 \text{ g/mol}}$

5) MgCl₂
* Mg: 24.31
* Cl: $35.45 \times 2 = 70.90$
* Total: $24.31 + 70.90 = \mathbf{95.21 \text{ g/mol}}$

6) (NH₄)₂SO₄
* N: $14.01 \times 2 = 28.02$
* H: $1.01 \times 8 = 8.08$ (because there are 4 H inside the parenthesis, multiplied by 2 outside)
* S: 32.06
* O: $16.00 \times 4 = 64.00$
* Total: $28.02 + 8.08 + 32.06 + 64.00 = \mathbf{132.16 \text{ g/mol}}$

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Part 2: Mole Conversions

*Rule: To find moles, divide grams by molar mass. To find grams, multiply moles by molar mass.*

1) How many moles are in 15 grams of lithium?
* Molar Mass of Li: 6.94 g/mol
* Calculation: $15 \div 6.94$
* Answer: 2.16 moles

2) How many grams are in 2.4 moles of sulfur?
* Molar Mass of S: 32.06 g/mol
* Calculation: $2.4 \times 32.06$
* Answer: 76.94 grams

3) How many moles are in 22 grams of argon?
* Molar Mass of Ar: 39.95 g/mol
* Calculation: $22 \div 39.95$
* Answer: 0.55 moles

4) How many grams are in 88.1 moles of magnesium?
* Molar Mass of Mg: 24.31 g/mol
* Calculation: $88.1 \times 24.31$
* Answer: 2,141.71 grams

5) How many moles are in 2.3 grams of phosphorus?
* Molar Mass of P: 30.97 g/mol
* Calculation: $2.3 \div 30.97$
* Answer: 0.074 moles

6) How many grams are in 11.9 moles of chromium?
* Molar Mass of Cr: 52.00 g/mol
* Calculation: $11.9 \times 52.00$
* Answer: 618.8 grams

7) How many moles are in 9.8 grams of calcium?
* Molar Mass of Ca: 40.08 g/mol
* Calculation: $9.8 \div 40.08$
* Answer: 0.24 moles

8) How many grams are in 238 moles of arsenic?
* Molar Mass of As: 74.92 g/mol
* Calculation: $238 \times 74.92$
* Answer: 17,830.96 grams

Final Answer:
See the step-by-step calculations above for the complete answers to all sections.