Answers

 

Explanation

Again, you should know your units of quantity by now, and one of the objectives of these MCQs is to make sure you have them at your fingertips.

Q 39.    If CaCl₂ has a relative molecular mass of 111, then 1 mole = 111g, and 1.11g is equal to N moles.
So 111g × N moles = 1.11g
N moles = 1.11g ÷111g.mol^-1 = 0.01 moles (the gram cancel each other out)
0.01 moles = 10^-2 moles = 10 × 10^-3 = 10 mmol
Make sure you work through the factors of 10.

Q 40.    The relative molecular mass of palmitic acid is 256. Therefore to obtain 1 mmol of palmitic acid you would weigh out:
This question is simply the reverse of Q 39.
If 1 mole of palmitric acid is 256g, 1 mmol = 256g x 10^-3 = 0.256g

Q 41.     The relative molecular mass of sucrose is 342. Therefore to obtain 1 mmol of sucrose you should weigh out:
This question extends upon Q 40.
If 1 mole of sucrose is 342g, 1 mmol = 342 x 10^-6 g = 0.000342g
This is not one of the answers, but 342g x 10^-6 g = 342 mg is

The rest of the questions all follow the same theme.
Be careful with your units, and don't forget that units such as mmol.l^-1 means mmol per litre, which is a volume and not an amount.