Applied Science: Unit 2 A- titrations and standard solutions

Unit 2: a- Practical Scientific Procedures and Techniques
Titration and standard solutions
A standard solution is a solution that contains a known and accurate amount
(concentration) of a substance or an element. The solution is used to hep and identify the
concentration of a substance. Standard solutions contain accurate concentrations of a
chemical component, so they will help in being as accurate as possible with the results, as
they will be accurate in determining the substances with unknown concentrations.
Titrations is a technique which is used to determine the concentration of a sample of an
acid, or a base, by neutralising it with an acid or a base of a known concentration. This
experiment is carried out using a burette (a piece of equipment).

Calculations for making our standard solution of sodium carbonate:
For making a standard solution of sodium carbonate, we need 0.5 moles of sodium
carbonate. However, we need to work out the number of grams of sodium carbonate
needed to make the solution.
Firstly, you need to calculate the Mr of sodium carbonate:
 You add together the atomic mass of each element in the molecule (Na2CO3).
Na2C03 contains: 2 atoms of Na, 1 atom of C and 3 atoms of O.
 The atomic mass of Na= 23. C= 12 and O= 16.
 The Mr of sodium carbonate= (23x2) + (12) + (16x3) = 106.

Now we can work out the mass of sodium carbonate.

The equation for working out the mass is the following:
 Mass= Moles x Molar mass
 Mass= 0.5 x 106= 53g
 Note that 53g of sodium carbonate is needed to make 1 litre of solution.
 However, we will be using 250 ml instead.
 250ml= 13.25g of Na2CO3 (sodium carbonate).



Method for making a standard solution:
We will prepare a solution of sodium carbonate that has a known concentration of
0.5 mol/dm-3.
The procedure consists this order of steps:
1. First calculate the mass of solid sodium carbonate needed to produce 25 cm3 of
a solution of 0.500 moldm-3; as shown above.
2. Use a spatula to put 13.25g of sodium carbonate into a clean and dry weighing
boat. The weighing boat should be on a balance already; the balance should be
reset to zero, for accurate measurements.

, 3. Make sure all the sodium carbonate has been poured into the beaker, ensure
that there is no left over.
4. Then, add 100cm3 of distilled water to the beaker that contains the solid sodium
carbonate. Use a glass rod to stir the contents of the beaker until of the solid
dissolves.
5. Use a funnel to pour the contents of the beaker into 250cm3 volumetric flask;
use a wash bottle to rinse the beaker and funnel into the same volumetric flask.
Rinse the glass rod into these washings.
6. Carefully add distilled water from the wash bottle to make the volumetric flask
go up to the graduated mark. Make sure to not overshoot the mark.
7. But a stopper on the volumetric flask and shake it thoroughly to mix the contents
of the flask.



Risk assessment for making a standard solution:




Titration Method, Calculations and Risk Assessment:

Method:
Here are four simple steps, used to make a titration
1. You will need to pour 25cm3 of your sodium carbonate solution into
250cm3 capacity conical flask. You can measure the volume by using a
measuring cylinder.
2. Next, titrate with the hydrochloric acid. The end of titration can be
observed when the solution changes from pink to colourless. Note the
titre and then add only a few drops of methyl orange.