Examples of Calculating Percentage Concentration Problems

🧪 Quick Study Guide

• ⚖️ Percentage concentration expresses the amount of solute relative to the total amount of solution as a percentage.
• ⚗️ There are three main types:
  • Weight/Weight (w/w)%: Mass of solute per 100 units of mass of solution.
  • Volume/Volume (v/v)%: Volume of solute per 100 units of volume of solution.
  • Weight/Volume (w/v)%: Mass of solute per 100 units of volume of solution.
• 🔢 The formulas are:
  • $(w/w)\% = \frac{\text{mass of solute}}{\text{mass of solution}} \times 100$
  • $(v/v)\% = \frac{\text{volume of solute}}{\text{volume of solution}} \times 100$
  • $(w/v)\% = \frac{\text{mass of solute (g)}}{\text{volume of solution (mL)}} \times 100$
• 📝 Remember to ensure units are consistent before calculating. For example, convert everything to grams and milliliters!
• 💡 When calculating the mass of solution, it's the sum of the solute and solvent masses: $\text{mass of solution} = \text{mass of solute} + \text{mass of solvent}$. Similarly for volumes.

Practice Quiz

1. A solution is prepared by dissolving 25 g of NaCl in 100 g of water. What is the weight/weight (w/w)% concentration of NaCl in the solution?
   1. 15%
   2. 20%
   3. 25%
   4. 30%
2. What is the volume/volume (v/v)% concentration of a solution prepared by mixing 50 mL of ethanol with enough water to make 200 mL of solution?
   1. 15%
   2. 20%
   3. 25%
   4. 30%
3. A 5% (w/v) solution of glucose is prepared. How many grams of glucose are needed to make 500 mL of this solution?
   1. 15 g
   2. 20 g
   3. 25 g
   4. 30 g
4. If you have a 10% (w/w) solution of KCl, how many grams of KCl are present in 50 g of the solution?
   1. 3 g
   2. 4 g
   3. 5 g
   4. 6 g
5. A solution is made by dissolving 10 mL of acetic acid in 90 mL of water. What is the volume/volume (v/v)% concentration of acetic acid?
   1. 5%
   2. 10%
   3. 15%
   4. 20%
6. How many grams of NaOH are required to prepare 250 mL of a 4% (w/v) NaOH solution?
   1. 8 g
   2. 10 g
   3. 12 g
   4. 14 g
7. If a solution is 20% (w/w) in solute, what mass of the solution contains 40 g of the solute?
   1. 100 g
   2. 150 g
   3. 200 g
   4. 250 g