2: Solutions
Students prepare solutions from solids or stock reagents by calculating grams needed for a target molarity, using formula weight, and converting between mass concentration, percent w/v, percent v/v, and molarity.
Mass for a Target Concentration
Click to show Mass for a Target Concentration example problem
| Sodium bicarbonate (NaHCO3) | |
| Volume | 55.0 mL |
| Concentration | 2.0 mg/mL |
| Molecular weight | 84.01 g/mol |
| State | Solid powder at room temperature |
How many milligrams (mg) of sodium bicarbonate (NaHCO3) would you need to make 55.0 mL of a 2.0 mg/mL NaHCO3 solution?
Note: answers need to be within 1% of the correct number to be correct.
Mass for Weight/Volume Solutions
Click to show Mass for Weight/Volume Solutions example problem
| Sodium chloride (NaCl) | |
| Volume | 450 mL |
| Concentration | 12% (w/v) |
| Molecular weight | 58.44 g/mol |
| State | Solid powder at room temperature |
How many grams (g) of sodium chloride (NaCl) you would need to make 450 mL of a 12% (w/v) NaCl solution?
Note: answers need to be within 2% of the correct number to be correct.
Mass for Solutions Using Molarity and Molecular Weight
Click to show Mass for Solutions Using Molarity and Molecular Weight example problem
| sucrose | |
| Volume | 7 mL |
| Concentration | 250 mM |
| Molecular weight | 342.30 g/mol |
| State | Solid powder at room temperature |
How many milligrams (mg) of sucrose would you need to make 7 mL of a 250 mM sucrose solution?
Note: answers need to be within 1% of the correct number to be correct.
Solute Volume for Percent Volume/Volume Solutions
Click to show Solute Volume for Percent Volume/Volume Solutions example problem
| acetone | |
| Volume | 50 mL |
| Concentration | 70% (v/v) |
| Molecular weight | 58.08 g/mol |
| State | Liquid at room temperature |
How many milliliters (mL) of acetone you would need to make 50 mL of a 70% (v/v) acetone solution?
Note: answers need to be within 3% of the correct number to be correct.