Given the concentration and volume of a solution of A
Find the mass of B
A summary of one approach to solving stoichiometry problems
Stoichiometry problems are often concerned with two substances involved in a chemical reaction.
The problems in this module are of this type and you will be
Identify the Known substance.Identify the Unknown substance.
Assign symbols to the given data and to the unknown quantity.
Connect the Known and Unknown by identifying any intermediate quantities that need to be calculated.
Identify the mathematical relationships required to do each step of the calculation.
Stoichiometry problems are often concerned with two substances involved in a chemical reaction.
The problems in this module are of this type and you will be
given the concentration or volume of one substance (the known) and asked to find the mass of a second substance (the unknown).
. Identify the Known substance.
n = c × V
Enough information is given to calculate the amount in moles (n) of the Known.
The amount in moles can be calculated from the concentration (c) and volume (V) of a solution.
The amount in moles can be calculated from the concentration (c) and volume (V) of a solution.
Assign symbols to the given data and to the unknown quantity.
Be sure to include the substance to which each symbol refers, for example m(NaOH).
This helps you to connect the data to any mathematical relationships that you have learned.
This helps you to connect the data to any mathematical relationships that you have learned.
Connect the Known and Unknown by identifying any intermediate quantities that need to be calculated.
As shown in the plan below, the known and the unknown are related through their amounts in moles.
| n(A) | = | n(B) |
| a | b |
The amounts in moles of any pair of substances are related by their coefficients in the balanced equation.
Consider the example where substance A and B react according to aA + bB
cC + dD
a, b, c and d are coefficients in the balanced equation.
Consider the example where substance A and B react according to aA + bB
cC + dD a, b, c and d are coefficients in the balanced equation.
| Known substance A | Unknown substance B | |||||
| c(A) and V(A) concentration and volume of A | step 1 | n(A) moles of A | step 2 | n(B) moles of B | step 3M(B) | m(B) mass of B |
Identify the mathematical relationships required to do each step of the calculation.
m = n × M
The relationships required in Steps 1 and 2 are given above.
Mass can be calculated from the amount in moles (n) if the molar mass (M) of the substance is known.
Mass can be calculated from the amount in moles (n) if the molar mass (M) of the substance is known.