Question 1

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

Accepted Answer

The ratio of the moles of the component to the total moles of all components in the solution.

Question 2

Given 25.0 g of dichloromethane ($$\mathrm{CH_2Cl_2}) $$dissolved in 125 g of water, what is the mole fraction of dichloromethane? (Molar masses: $$\mathrm{CH_2Cl_2} = 84.93\ \mathrm{g/mol}$$, $$\mathrm{H_2O} = 18.02\ \mathrm{g/mol})$$

Accepted Answer

$$0.0407$$

Question 3

A reaction vessel contains 20.3 g $$\mathrm{Cl_2$}$$, 4.27 g $$\mathrm{Ne}$$, and 10.8 g $$\mathrm{O_2$}. $$What is the mole fraction of nitrogen if 5.00 g $$\mathrm{N_2$} is $$also present? (Molar masses: $$\mathrm{Cl_2$} = 70.90\ \mathrm{g/mol}$$, $$\mathrm{Ne} = 20.18\ \mathrm{g/mol}$$, $$\mathrm{O_2$} = 32.00\ \mathrm{g/mol}$$, $$\mathrm{N_2$} = 28.02\ \mathrm{g/mol})$$

Accepted Answer

$$0.0597$$

Question 4

If the mole fraction of water in a solution is $$0.96$$, what is the mole fraction of all other components combined?

Accepted Answer

$$0.04$$

Question 5

Which of the following statements about mole fraction is correct?

Accepted Answer

Mole fraction is a dimensionless quantity.

Question 6

A solution is prepared by dissolving $$10.0\ \mathrm{g} of$$ $$\mathrm{NaCl} ($$molar mass $$58.44\ \mathrm{g/mol}) in$$ $$90.0\ \mathrm{g} of $$water (molar mass $$18.02\ \mathrm{g/mol}). $$What is the mole fraction of $$\mathrm{NaCl}$$?

Accepted Answer

$$0.019$$

Question 7

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

Accepted Answer

To avoid significant rounding errors that can affect the accuracy of experimental results.

Question 8

Which of the following is the correct formula for mole fraction ($$X) of $$component A in a mixture?

Accepted Answer

$$X_A = \frac{n_A}{n_{total}}$$

Question 9

A chemist prepares a solution by mixing $$2.00\ \mathrm{mol} of $$ethanol with $$8.00\ \mathrm{mol} of $$water. What is the mole fraction of ethanol in the solution?

Accepted Answer

$$0.20$$

Question 10

If a solution contains $$0.3944$$ mol $$\mathrm{CH_2Cl_2}$$ and $$6.9383$$ mol $$\mathrm{H_2O}$$, what is the mole fraction of $$\mathrm{CH_2Cl_2}$$?

Accepted Answer

$$0.0407$$

Question 11

A student calculates the mole fraction of a solute as $$1.2. $$What is the most likely error in their calculation?

Accepted Answer

They used the moles of solute as the denominator instead of the total moles.

Question 12

In a mixture of gases, the mole fraction of oxygen is $$0.21. If $$the total number of moles is $$10.0$$, how many moles of oxygen are present?

Accepted Answer

$$2.1$$

Question 13

Which of the following real-life scenarios best illustrates the use of mole fraction?

Accepted Answer

Calculating the concentration of oxygen in the air for scuba diving tanks.

Question 14

A solution is made by dissolving $$5.00\ \mathrm{g} of $$glucose ($$\mathrm{C_6H_{12}O_6$}$$, molar mass $$180.16\ \mathrm{g/mol}) in$$ $$100.0\ \mathrm{g} of $$water. What is the mole fraction of glucose?

Accepted Answer

$$0.0027$$

Question 15

If the mole fraction of a solute in a solution is doubled, what happens to the mole fraction of the solvent?

Accepted Answer

It decreases.

Mole Fraction Calculations in Solutions

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