Unit 2: Practical Scientific Procedures and Techniques
Assignment A: Keeping up the standards
Introduction :
Colorimetry is the process of finding out how much substance there is in a solution, in order
to be more precise. Colorimetry is also known as the technique to measure the intensity of
the colour, as the level of colour in a solution can determine the value of its concentration as
the intensity of the colour from a chemical reaction is proportional to the concentration of the
substance tested. A colorimeter is what you would use to find the value for the concentration
of a substance.
Figure 1 : Labelled diagram of colorimeter and the process.
The application of colorimetry in real life are colour printing, textile manufacturing, paint
manufacturing, food industries, blood sampling, water, soil nutrients and bacterial crop
growth.
Standard solutions are solutions that contain a precisely known amount of concentration of
an element or substance. A known weight of solute is dissolved in the solvent to make a
specific volume. This is important as we are able to have a solution in which we know the
precise amount of concentration, this will help us to determine the concentration of an
unknown substance.
In order to make a standard solution you will firstly need to calculate the mass of the
solution, this is calculated by the number of moles (cm³) = concentration (m/dm³) x volume
(dm³ or cm³). To get cm³ into dm³ you will need to divide by 1000.
Secondly, you are required to measure out the mass of the salt using a top pan balance.
You will place the beaker onto the top pan balance, ensuring that the grams are set to zero.
Then you will add the amount needed of the solution with a spatula. Whenever using a
container you will only take the lid off when you need to use it, then place it back in order to
avoid cross contamination.
, Unit 2: Practical Scientific Procedures and Techniques
Assignment A: Keeping up the standards
Third step, will require a baker to be filled with 1000 cm³ of distilled water. Distilled meaning
that the water has not got any impurities. You will also need to measure out the bottom of
the meniscus in order for accuracy.
Fourth step will require for the solution to be mixed with distilled water, whilst using a stirring
rod to stir the solution till fully dissolved. In order to speed up the process you are able to use
a bunsen burner in order to dissolve the solution faster.
Before taking out the rod, make sure to tap against the beaker in order for all droplets to fall
back into the beaker. If not then the results will be incorrect. When pouring the solution into
the volumetric flask, shake it slightly for all droplets to fall into the volumetric flask.
Lastly you will need to label the volumetric flask, by writing the solutions name, the mole
number, concentration and volume.
Creating a standard solution of copper sulphate (CuSO₄) :
1. Firstly you will need to calculate the mass of the solution or substance, you will need
to use the equation : number of moles = concentration x volume and
atomic weight ÷ 1000 cm³ x 100 = mass of CuSO₄ needed per 100 cm³. In order to
convert cm³ into dm³ you will need to divide by 1000.
So, in this case you will find out the atomic weight of Copper, Sulphate and Oxygen.
Copper : 63
Sulphur : 32
Oxygen : 16
The volume is 100cm³, and the concentration is 0.5mol/dm³. 100 divided by 1000 =
0.1dm3.
Moles = 0.1 x 0.5 = 0.05 moles
Mr of copper sulphate = 63.5 + 32.1 +(16 x 4) = 159.6
159.6 x 0.05 = 7.98g
159 divide by 1000 x 100 = 15.9g
This is a volume of 100cm³ with 1mol.dm³ concentration.
15.9g divided by 2 = 7.95g
This is a volume of 100cm³ with 0.5mol.dm³
2. You will gather your substance, which is Copper sulphate, you will need a top pan
balance in order to measure out the mass. Remember that once you have taken out
the substance you must close the lid in order to prevent cross contamination.
3. After this you will need to fill a 100 cm³ beaker with distilled water.
4. You will add the CuSO₄ into the beaker with distilled water, and whilst using a stirring
rod you will stir till the substance dissolves. In order to dissolve faster you could use
a bunsen burner to heat it up.
5. Before taking the rod out make sure to tap it against the beaker in order to get off any
droplets left of the solution in order to be as accurate as possible.
6. You will then pour the solution into the volumetric flask, shaking it slightly in order to
get all of the solution.
7. Lastly you would label the solutions name, the mole, concentration and volume.
