A scheme summarizing the approach to solving the three-step problems in this module is shown below. Using this scheme
concentration and volume of a known substance can be related to
concentration or volume of an unknown substance if the two substances are involved in a reaction for which the balanced equation is known.
n =
c × V (mol
–1 ×
= mol)
from known volume and concentration
Step 1: Calculate the amount in moles of the known substance using
For aA + bB → cC + dD
| n(A) | = | n(B) | = | n(C) | = | n(D) |
| a | b | c | d |
A, B, C and D substances; a, b, c, d coefficients
Step 2: Relate calculated n(known) to n(unknown) using any pair from
c =
n/
Vif volume is known and
concentration is unknown
V =
n/
cif volume is unknown and
concentration is known
Step 3: From n(unknown) calculate the desired quantity using