Acids and Bases

[Scienuk]

The answer is B;

Can you fully explain the question and how it is solved, thanks!

[kw0573]

Concepts tested: conversions between units, dilution concentration (Cv = Cv), concentration to pOH, pOH to pH. 

1) so 1 dm³ = 1 dm * 1 dm * 1 dm = 10 cm * 10 cm * 10 cm = 1000 cm³. 10.0 cm³ thus is equal to 0.0100 dm³. and that is being diluted to 1 dm³ (hundred times). That means the concentration is hundred times more dilute. so it would be 10^-4 mol dm^-3 instead of 10^-2. (Alternatively you can use Cv = Cv.)

2) pOH = -log (10^-4) = 4. pH and pOH always use concentrations in mol dm^-3. So if question was being extra tricky, remember to convert the concentration units as well. Now use pH + pOH = 14; pH + 4 = 14, pH = 10. 

The question can also be done in a different order, such as by using [H⁺][OH^-1] = 10^-14 and find [H⁺] directly instead of using pOH. However, the first step is to make sure that your units match with all the givens, with what the question asks for, and with what the formula is applicable to.