Percent composition

You’ve probably seen labels like “5% acetic acid” on a bottle of vinegar, “3% hydrogen peroxide” on a bottle of hydrogen peroxide, or “5% sodium hypochlorite” on a bottle of bleach. Those percentages are expressing the concentration of that particular solute in each solution. Percentage is the amount per 100. Depending on the way you choose to express the percentage, the units of amount per one hundred vary. Three different percentages are commonly used:

✓ Weight/weight (w/w) percentage

✓ Weight/volume (w/v) percentage

✓ Volume/volume (v/v) percentage

Unfortunately, although the percentage of solute is often listed, the method (w/w, w/v, v/v) is not. In this case, I normally assume that the method is weight/weight, but I’m sure you know about assumptions.