Q: A student is preparing a solution and needs to convert 42,000 g/mol to grams for 1.2 moles. Which calculation correctly determines the mass required?

$$42,000 \ \mathrm{g/mol} \times 1.2 \ \mathrm{mol} = 50,400 \ \mathrm{g}$$

Q: Given a molecular weight of $$42,000 \ \mathrm{g/mol}$$, how many grams are needed to make a $$0.5 \ \mathrm{mol}$$ solution?

$$42,000 \ \mathrm{g/mol} \times 0.5 \ \mathrm{mol} = 21,000 \ \mathrm{g}$$

Q: If you are given $$92,700 \ \mathrm{g/mol} as $$the molar mass of a protein, how many grams are in $$0.25 \ \mathrm{mol}$$?

$$92,700 \ \mathrm{g/mol} \times 0.25 \ \mathrm{mol} = 23,175 \ \mathrm{g}$$

Q: A researcher needs to prepare $$2.5 \times 10^4$ grams of a compound with a molar mass of 42$$,000 \ \mathrm{g/mol}$$. How many moles does this represent?

$$\frac{2.5 \times 10^4$ \ \mathrm{g}}{42,000 \ \mathrm{g/mol}} = 0.595 \ \mathrm{mol}$$

Q: If you need to prepare $$1.34 \ \mathrm{mol} of a $$compound with a molar mass of $$42,000 \ \mathrm{g/mol}$$, how many grams do you need?

$$1.34 \ \mathrm{mol} \times 42,000 \ \mathrm{g/mol} = 56,280 \ \mathrm{g}$$

Q: A laboratory protocol requires $$0.7 \ \mathrm{mol} of a $$protein with a molar mass of $$92,700 \ \mathrm{g/mol}. $$How many grams of protein are needed?

$$0.7 \ \mathrm{mol} \times 92,700 \ \mathrm{g/mol} = 64,890 \ \mathrm{g}$$

Q: A student mistakenly uses the formula $$\text{grams} = \frac{\text{moles}}{\text{molar mass}}$$ instead of $$\text{grams} = \text{moles} \times \text{molar mass}. $$What is the likely result if they try to calculate the mass of $$2 \ \mathrm{mol} of a$$ $$42,000 \ \mathrm{g/mol}$$ compound?

$$\frac{2}{42,000} = 4.76 \times 10$$^{-5}$$ \ \mathrm{g}$$, which is much too small

Question 1

A student is preparing a solution and needs to convert 42,000 g/mol to grams for 1.2 moles. Which calculation correctly determines the mass required?

Accepted Answer

$$42,000 \ \mathrm{g/mol} 	imes 1.2 \ \mathrm{mol} = 50,400 \ \mathrm{g}$$

Question 2

If you have 92.7 kDa of a protein and want to know how many grams this is per mole, which of the following is correct? (1 Da = 1 g/mol)

Accepted Answer

$$92,700 \ \mathrm{g/mol}$$

Question 3

A calculation yields a value of 1.34. If this represents the concentration in mol/L, which of the following best describes the solution?

Accepted Answer

The solution has a concentration of $$1.34 \ \mathrm{mol/L}.$$

Question 4

Given a molecular weight of $$42,000 \ \mathrm{g/mol}$$, how many grams are needed to make a $$0.5 \ \mathrm{mol}$$ solution?

Accepted Answer

$$42,000 \ \mathrm{g/mol} 	imes 0.5 \ \mathrm{mol} = 21,000 \ \mathrm{g}$$

Question 5

If you are given $$92,700 \ \mathrm{g/mol} as $$the molar mass of a protein, how many grams are in $$0.25 \ \mathrm{mol}$$?

Accepted Answer

$$92,700 \ \mathrm{g/mol} 	imes 0.25 \ \mathrm{mol} = 23,175 \ \mathrm{g}$$

Question 6

A researcher needs to prepare $$2.5 	imes 10^4$ grams of a compound with a molar mass of 42$$,000 \ \mathrm{g/mol}$$. How many moles does this represent?

Accepted Answer

$$\frac{2.5 	imes 10^4$ \ \mathrm{g}}{42,000 \ \mathrm{g/mol}} = 0.595 \ \mathrm{mol}$$

Question 7

If a protein has a molar mass of $$92,700 \ \mathrm{g/mol}$$ and you have $$18.54 \ \mathrm{g}$$, how many moles of protein do you have?

Accepted Answer

$$\frac{18.54 \ \mathrm{g}}{92,700 \ \mathrm{g/mol}} = 2.00 	imes 10$$^{-4}$$ \ \mathrm{mol}$$

Question 8

A solution is prepared by dissolving $$25,000 \ \mathrm{g} of a $$compound with a molar mass of $$42,000 \ \mathrm{g/mol} in $$enough water to make $$1.0 \ \mathrm{L} of $$solution. What is the molarity of the solution?

Accepted Answer

$$\frac{25,000 \ \mathrm{g}}{42,000 \ \mathrm{g/mol}} = 0.595 \ \mathrm{mol}$$, so $$0.595 \ \mathrm{M}$$

Question 9

If you need to prepare $$1.34 \ \mathrm{mol} of a $$compound with a molar mass of $$42,000 \ \mathrm{g/mol}$$, how many grams do you need?

Accepted Answer

$$1.34 \ \mathrm{mol} 	imes 42,000 \ \mathrm{g/mol} = 56,280 \ \mathrm{g}$$

Question 10

A laboratory protocol requires $$0.7 \ \mathrm{mol} of a $$protein with a molar mass of $$92,700 \ \mathrm{g/mol}. $$How many grams of protein are needed?

Accepted Answer

$$0.7 \ \mathrm{mol} 	imes 92,700 \ \mathrm{g/mol} = 64,890 \ \mathrm{g}$$

Question 11

A student mistakenly uses the formula $$	ext{grams} = \frac{	ext{moles}}{	ext{molar mass}}$$ instead of $$	ext{grams} = 	ext{moles} 	imes 	ext{molar mass}. $$What is the likely result if they try to calculate the mass of $$2 \ \mathrm{mol} of a$$ $$42,000 \ \mathrm{g/mol}$$ compound?

Accepted Answer

$$\frac{2}{42,000} = 4.76 	imes 10$$^{-5}$$ \ \mathrm{g}$$, which is much too small

Question 12

If a protein solution is labeled as $$1.34 \ \mathrm{mol/L}$$, how many grams of a $$92,700 \ \mathrm{g/mol}$$ protein are present in $$500 \ \mathrm{mL}$$?

Accepted Answer

$$1.34 \ \mathrm{mol/L} 	imes 0.5 \ \mathrm{L} = 0.67 \ \mathrm{mol}$$; $$0.67 \ \mathrm{mol} 	imes 92,700 \ \mathrm{g/mol} = 62,109 \ \mathrm{g}$$

Calculations Involving Molar Mass and Unit Conversions in Biochemistry

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