Concentration of Solutions Problems

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Questions and Answers

Which of the following is the correct formula for calculating percent by mass?

$rac{ ext{Volume of solute}}{ ext{Volume of solution}} imes 100$

$rac{ ext{Mass of solute}}{ ext{Mass of solvent}} imes 100$

$rac{ ext{Mass of solvent}}{ ext{Mass of solution}} imes 100$

$rac{ ext{Mass of solute}}{ ext{Mass of solution}} imes 100$ (correct)

In Sample Problem 2, what is the percent by mass of salt in the saltwater solution?

27.3%

60.0%

45.0%

37.5% (correct)

What is the percent by volume of alcohol in the lambanog solution described in Sample Problem 1?

25%

33.3% (correct)

50%

66.7%

In Sample Problem 3, what is the percent by mass of ammonium nitrate in the solution?

16.5% Signup and view all the answers

What is the percent by volume of the isopropanol and water solution in Sample Problem 3?

45.5% Signup and view all the answers

What is the typical percent by volume of alcohol in beer?

5.0% Signup and view all the answers

Which of the following is the correct formula for calculating the mole fraction of the solute in a solution?

$x_{solute} = \frac{moles\ solute}{moles\ solute + moles\ solvent}$ Signup and view all the answers

What is the relationship between the mole fractions of the solute and solvent in a solution?

The sum of the mole fractions of the solute and solvent is always equal to 1. Signup and view all the answers

What is the molarity of a solution that contains 0.75 mol of solute dissolved in 2.50 L of solution?

1.88 M Signup and view all the answers

A solution contains 6.60 grams of C6H12O6 in 150.0 mL of solution. What is the molarity of this solution?

2.20 M Signup and view all the answers

What is the molarity of a 45% by mass aqueous CaCl2 solution with a density of 1.2 g/mL? The molar mass of CaCl2 is 111 g/mol.

3.06 M Signup and view all the answers

What is the molality of a solution that contains 12.5 grams of NaOCl in 1000 mL of solution?

1.11 m Signup and view all the answers

What is the mole fraction of HCl in an aqueous solution that contains 44.2 grams of HCl and 88.6 grams of H2O?

0.20 Signup and view all the answers

A solution is prepared by dissolving 4.5 g of methanol (CH3OH) in 40 g of water. What is the mole fraction of methanol in this solution?

0.10 Signup and view all the answers

A hydrochloric acid (HCl) solution contains 30% HCl by weight. What is the mole fraction of HCl in this solution?

0.40 Signup and view all the answers

What is the mole fraction of MgBr2 and H2O in a solution that contains 28.67 moles of MgBr2 and 90.71 moles of H2O?

0.24 and 0.76 Signup and view all the answers

Study Notes

Percent by Mass

The formula for percent by mass is: (mass of solute / total mass of solution) × 100%
Example calculation: For salt in a saltwater solution, the percent by mass can be determined using the specific mass values provided in the sample problem.

Percent by Volume

Percent by volume is calculated as: (volume of solute / total volume of solution) × 100%
Typical volume of alcohol in beer is around 4-6% by volume.

Mole Fraction

The correct formula for calculating the mole fraction of a solute is: (moles of solute / (moles of solute + moles of solvent))
The mole fractions of solute and solvent add up to 1: X_solute + X_solvent = 1

Molarity Calculations

Molarity (M) is defined as: moles of solute / liters of solution
Example: A solution with 0.75 mol of solute in 2.50 L has a molarity of 0.30 M.
A solution with 6.60 grams of C6H12O6 in 150.0 mL needs the molar mass of C6H12O6 to find its molarity.

Specific Molarity Examples

For a 45% by mass CaCl2 solution with a density of 1.2 g/mL, use the mass percent and density to calculate molarity.
The molar mass of CaCl2 is 111 g/mol; this is required for calculations.

Molality

Molality (m) is defined as: moles of solute / mass of solvent in kg.
Example: To find molality for 12.5 grams of NaOCl in 1000 mL, convert grams to moles and solve.

Mole Fraction in Solutions

For HCl in a solution with 44.2 grams of HCl and 88.6 grams of H2O, calculate moles of each component to find mole fraction of HCl.
For a solution with 4.5 g of methanol in 40 g of water, use the respective molar masses to find mole fractions.

Example Mole Fractions

The mole fraction of HCl in a 30% by weight HCl solution can be derived from the mass percentages.
A solution with 28.67 moles of MgBr2 and 90.71 moles of H2O can yield the mole fractions for both components through basic mole fraction calculations.

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Description

Test your understanding of concentration units in solutions with problems involving percent by mass, percent by volume, mole fraction, molarity, and molality. Practice calculating the percent by mass of various solutes in different solution scenarios.