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

Study Guide - Practice Questions

Study Guide - Flashcards