Making a Volumetric Solution (AQA A Level Chemistry)
Revision Note
Making a Volumetric Solution
REQUIRED PRACTICAL 1
Volumetric Analysis
Volumetric analysis is a process that uses the volume and concentration of one chemical reactant (a volumetric solution) to determine the concentration of another unknown solution
The technique most commonly used is a titration
The volumes are measured using two precise pieces of equipment, a volumetric or graduated pipette and a burette
Before the titration can be done, the standard solution must be prepared
Specific apparatus must be used both when preparing the standard solution and when completing the titration, to ensure that volumes are measured precisely
Some key pieces of apparatus used to prepare a volumetric solution and perform a simple titration
Beaker
Burette
Volumetric Pipette
Conical Flask
Volumetric Flask
Making a Volumetric Solution
Chemists routinely prepare solutions needed for analysis, whose concentrations are known precisely
These solutions are termed volumetric solutions or standard solutions
They are made as accurately and precisely as possible using three decimal place balances and volumetric flasks to reduce the impact of measurement uncertainties
The steps are:
Volumes & concentrations of solutions
The concentration of a solution is the amount of solute dissolved in a solvent to make 1 dm3 of solution
The solute is the substance that dissolves in a solvent to form a solution
The solvent is often water
A concentrated solution is a solution that has a high concentration of solute
A dilute solution is a solution with a low concentration of solute
Concentration is usually expressed in one of three ways:
moles per unit volume
mass per unit volume
parts per million
Worked Example
Calculate the mass of sodium hydroxide, NaOH, required to prepare 250 cm3 of a 0.200 mol dm-3 solution
Answer:
Step 1: Find the number of moles of NaOH needed from the concentration and volume:
number of moles = concentration (mol dm-3) x volume (dm3)
n = 0.200 mol dm-3 x 0.250 dm3
n = 0.0500 mol
Step 2: Find the molar mass of NaOH
M = 22.99 + 16.00 + 1.01 = 40.00 g mol-1
Step 3: Calculate the mass required
mass = moles x molar mass
mass = 0.0500 mol x 40.00 g mol-1 = 2.00 g
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