Question

A 3.0% (m/v) potassium chloride solution has a volume of 25.0 mL. How many moles of potassium chloride are in the sample?

I would answer this. But my teacher skimmed through this section of the text. And he won’t help me with it. I just know that m/v is g/ml and mLs should cancel out right? And moles come from mole/L. I am not sure what to do though.

Answer 1

Using your knowledge of m/v = g/mL, you can start by putting that in the equation as:


`(3g)/(100mL)`

And you know that the volume is 25 mL. So you could put this into the equation as:


`(25mL)/(1)`

And you also know that the molar mass of KCl is 74.55g (K = 39.1 g/mol and Cl = 35.45 g/mol. Add them together to get 74.55g/mol).

We can then put this in the equation as:


`(1mol)/(74.55g)`

Then, we can mulitply them all together:


`(3g)/(100mL)* (25mL)/(1) * (1mol)/(74.55g)=0.01 mol`

And now we know that there are 0.01 moles of KCl in the sample.