In this example question, it asks how many grams of sodium phosphate, which has a molecular mass of 163.94 grams per mole, are present in 300 milliliters of a 0.550 molar sodium phosphate solution. Now, before we start plugging in numbers and doing calculations, let's discuss what the sentence indicates and how we should interpret it when it's presented in such a way. We have several numbers, connected by the word "of". Remember, when "of" joins two values, it typically instructs us to multiply them together. Here, we encounter molarity, which is defined as moles over liters. If we multiply both sides by liters, it shows that moles equal liters times molarity.

Notice that the volume provided is in milliliters. To proceed, we need to convert milliliters to liters and then multiply by the molarity to determine the moles of sodium phosphate. Knowing the moles of a compound allows us to use its molecular mass to calculate the grams of that compound. We start by converting 300 milliliters into liters. This is a metric prefix conversion, where milliliters are converted to liters using the factor 1milli=10-3. Milliliters cancel out, leaving us with liters.

Molarity also acts as a conversion factor. The 0.550 molar indicates we have 0.550 moles of the compound per 1 liter. We need liters to cancel out, so we place 1 liter on the opposite side, resulting in an expression that just leaves moles of sodium phosphate. Converting these moles to grams, we use the given molecular weight of 163.94 grams per mole. Thus, the final step involves multiplying the moles by the molecular weight. Initially, this gives us 27.0501 grams of sodium phosphate.

Considering significant figures, 300.0 has four, 0.550 has three, and 163.94 has five. We use the least number of significant figures for our final answer, yielding 27.1 grams of sodium phosphate. So, when the problem gives us a volume of molarity, it essentially provides the moles. In this case, we simply converted those moles to grams to find the answer.