Subject: mL to grams
Name: Lisa
Who are you: Parent

We have 900mL and you have to multiply by 1.18 grams do you just multiply and get 1062 grams or am I missing a step?


Hi Lisa.

You aren't missing a step and your arithmetic is correct. It's just your units that are a bit awkward. With a problem involving just a couple of quantities, it's okay to keep track in your head, but it can cause trouble if you don't pay close attention to units with more complicated problems.

What you have is a volume (ml) and you want mass (grams). You can't multiply ml by grams and get grams, you have to also divide by ml. That is, the conversion factor you are using is actually grams per millilitre (g/ml) which is density, not mass. So converting from ml to grams is done by multiplying by the density of the substance in ml (and that varies depending on the substance you are measuring). If the density is 1.18 g/ml, you do indeed get 1062 g for a 900ml volume.

Stephen La Rocque.>