hydrogen peroxide?

Question

if you buy a 250 mL bottle of 3.0% H2O2 (m/v), how many grams of hydrogen peroxide have you purchased? also, what is the molarity of the solution?

Answer 1

250 mL H2O2 * 3.0 g /100 mL =
7.5 g of H2O2

7.5 g H2O2 * 1 mol H2O2 / 1.008 g H2O2 =
7.44 mol H202

7.44 mol H2O2 / .250 L = 29.8 M H2O2

Answer 2

m/v means mass/volume or weight/volume. So 3.0% m/v means 3 g/100mL or 3 kg/L.

250mL H2O2 x 3gH2O2/100mL H2O2 = (250)(3)/100 = gH2O2

The mL H2O2 cancel out, leaving gH2O2.

At. wts.: H=1 O=16 H2O2=34
Molarity means molH2O2/L H2O2 = molH2O2/1000mL H2O2. The answer has two parts, so you must use a two-part given. Start with:

3gH2O2/100mL H2O2 x 1molH2O2/34gH2O2 x 1000mL H2O2/1L H2O2 = (3)(1000)/(100)(34) = molH2O2/1L H2O2

In the first step, the gH2O2 cancel, leaving molH2O2, which is the "top" part of the answer. In the second step, the mL H2O2 cancel, leaving L H2O2, which is the "bottom" part of the answer.

Answer 3

Actually, after awhile, this can do more harm than good. Granted, using a toothpaste or whitening strip with hydrogen peroxide in it can work wonders because it is a small concentration of the compound and deeply cleans the teeth rather than bleaching the surface. However, gargling with straight peroxide will eventually dry out your teeth because of how powerful the chemical's cleansing is. It can lead to a condition known as decalcification which is basically the appearance of rather unattractive pale, creamy areas on the teeth. I wouldn't recommend using straight peroxide on a regular basis. Just once in awhile while you brush daily with a peroxide-based whitening toothpaste.