Take another look at the pathway between the
known mass of substance A and the
unknown concentration of substance B with which it reacts. The
volume of solution in which B is dissolved is known, and since a concentration is required in the last step, the calculated amount in moles of B is divided by the known volume.
| Known | | | |
| m(A) |  | n(A) |  |
| mass of A | Step 1 | moles of A | Step 2 |
| | | Unknown |
| n(B) |  | c(B) |
| moles of B | Step 3 | concentration of B |
A very similar pathway to that above has an unknown
volume of B and a known
concentration of B. There is only a small difference (in Step 3) between the approach to solving this type of problem and the problem above.
| Known | | | |
| m(A) |  | n(A) |  |
| mass of A | Step 1 | moles of A | Step 2 |
| | | Unknown |
| n(B) |  | V(B) |
| moles of B | Step 3 | concentration of B |