Question: how many moles of chlorine are in 25.0 g of calcium chloride (cacl2)?
Answer: First, convert 25.0 grams of calcium chloride to moles. There are two molecules of chlorine per molecule of CaCl2. So, multiply the above by two: 1.355 * 10^23 * 2 = 2.71 * 10^23 molecules of chlorine!