How do you do metric conversions?

Metric Conversions: How do I solve this?

• How many molecules are in one drop of alcohol if there are 3.34 x 10^22 molecules in 1.00 g ? (Given that 1 mL = 20 drops.)

• Answer:

  This is a little more problematic than it looks. First of you need to know which alcohol. I'll assume methanol because it and ethanol are the most common ones. Ethanol has a density of 0.8 about given mass = 1 gram density = 0.8 grams / mL volume = ???? Volume = mass / density = 1 / 0.8 = 1.25 mL 1 mL = 20 drops 1.25 mL = x x = 25 drops. 25 drops contain 3.34 * 10^22 molecules 1 drop contains x x = 1.34 * 10^21 molecules. This can all be done in one step if you know how to do dimensional analysis. 3.34 * 10^22 molecules / 1 gram [ 0.8 grams / mL] * [ 1 mL / 20 drops] = 1.34 * 10^21 molecules.