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 chloride (NaCl) | |
| Volume | 190.0 mL |
| Concentration | 2.5 mg/mL |
| Molecular weight | 58.44 g/mol |
| State | Solid powder at room temperature |
How many milligrams (mg) of sodium chloride (NaCl) would you need to make 190.0 mL of a 2.5 mg/mL NaCl 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
| Glucose | |
| Volume | 200 mL |
| Concentration | 7% (w/v) |
| Molecular weight | 180.16 g/mol |
| State | Solid powder at room temperature |
How many grams (g) of glucose (Glucose) you would need to make 200 mL of a 7% (w/v) Glucose solution?
Note: answers need to be within 7% 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
| Ethylenediaminetetraacetic acid (EDTA) | |
| Volume | 470 mL |
| Concentration | 3 mM |
| Molecular weight | 292.24 g/mol |
| State | Solid powder at room temperature |
How many milligrams (mg) of ethylenediaminetetraacetic acid (EDTA) would you need to make 470 mL of a 3 mM EDTA 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 | 90 mL |
| Concentration | 20% (v/v) |
| Molecular weight | 58.08 g/mol |
| State | Liquid at room temperature |
How many milliliters (mL) of acetone you would need to make 90 mL of a 20% (v/v) acetone solution?
Note: answers need to be within 5% of the correct number to be correct.