Question 1

Which of the following best describes the mole fraction ($$X) in a $$solution?

Accepted Answer

The ratio of the moles of a component to the total moles in the solution.

Question 2

Given 25.0 g of dichloromethane ($$\mathrm{CH_2Cl_2}) $$dissolved in 125 g of water ($$\mathrm{H_2O}$$), what is the first step in calculating the mole fraction of dichloromethane?

Accepted Answer

Convert the mass of dichloromethane to moles.

Question 3

If you have 2.50 g of $$\mathrm{CH_2Cl_2}$$, what is the number of moles present? (Molar mass of $$\mathrm{CH_2Cl_2} = 84.93 g/$$mol)

Accepted Answer

$$2.50 \div 84.93 = 0.0294$$ moles

Question 4

In the mole fraction formula $$X = \dfrac{	ext{mole component}}{	ext{total moles}}$$, what does the denominator represent?

Accepted Answer

The total number of moles of all substances present.

Question 5

A solution contains 0.3944 moles of $$\mathrm{Cl_2$}$$, 0.2294 moles of $$\mathrm{Ne}$$, and 0.0407 moles of $$\mathrm{O_2$}. $$What is the mole fraction of $$\mathrm{Ne}$$?

Accepted Answer

$$\dfrac{0.2294}{0.3944 + 0.2294 + 0.0407} = 0.345$$

Question 6

Why is it important to use at least 4 decimal places when calculating mole fractions?

Accepted Answer

To avoid rounding errors and maintain accuracy in calculations.

Question 7

If a solution contains 20.3 g $$\mathrm{Cl_2$} ($$molar mass = 70.90 g/mol), 4.27 g $$\mathrm{Ne} ($$molar mass = 20.18 g/mol), and 10.8 g $$\mathrm{O_2$} ($$molar mass = 32.00 g/mol), what is the mole fraction of $$\mathrm{O_2$}$$?

Accepted Answer

$$\dfrac{10.8 \div 32.00}{(20.3 \div 70.90) + (4.27 \div 20.18) + (10.8 \div 32.00)}$$

Question 8

Which of the following statements about mole fraction is FALSE?

Accepted Answer

Mole fraction can be greater than 1 for a component.

Question 9

A student calculates the mole fraction of $$\mathrm{CH_2Cl_2} in a $$solution and gets a value of 1.2. What is the most likely error?

Accepted Answer

They forgot to include all components in the denominator.

Question 10

In a mixture, the mole fraction of water is 0.75. What is the combined mole fraction of all other components?

Accepted Answer

$$1 - 0.75 = 0.25$$

Question 11

Which real-world scenario best illustrates the use of mole fraction in biochemistry?

Accepted Answer

Determining the mole fraction of oxygen in a gas mixture for respiration studies.

Question 12

A solution contains 0.0407 moles of $$\mathrm{O_2$}$$ and 0.3944 moles of $$\mathrm{Cl_2$}. $$What is the mole fraction of $$\mathrm{O_2$}$$?

Accepted Answer

$$\dfrac{0.0407}{0.3944 + 0.0407} = 0.093$$

Question 13

If the mole fraction of a solute in a solution is 0.04, what is the mole fraction of the solvent?

Accepted Answer

$$1 - 0.04 = 0.96$$

Question 14

Which step is essential to avoid rounding errors when calculating mole fractions?

Accepted Answer

Use at least 4 decimal places in your calculations.

Question 15

A solution is made by dissolving 5.00 g of $$\mathrm{NaCl} ($$molar mass = 58.44 g/mol) in 100.0 g of water (molar mass = 18.02 g/mol). What is the mole fraction of $$\mathrm{NaCl}$$?

Accepted Answer

$$\dfrac{5.00 \div 58.44}{(5.00 \div 58.44) + (100.0 \div 18.02)}$$

Question 16

Which of the following is NOT a correct use of the mole fraction concept?

Accepted Answer

Determining the mass percent of a solute.

Question 17

A biochemist needs to prepare a solution with a mole fraction of 0.10 for a solute. If the total moles in the solution must be 1.00, how many moles of solute are required?

Accepted Answer

$$0.10 	imes 1.00 = 0.10$$ moles

Question 18

If a solution contains 0.2294 moles of $$\mathrm{Ne}$$ and 0.0407 moles of $$\mathrm{O_2$}$$, what is the total number of moles in the solution?

Accepted Answer

$$0.2294 + 0.0407 = 0.2701$$ moles

Mole Fraction Calculations in Biochemistry Solutions

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