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Unit 22 – Assignment 1 – P1 & P2

Results
Mass of filter paper: 1
...
99g
Mass of dried crystals of product: 2
...
05
N of CuSO4 = 0
...
05 * 159
...
975g

Percentage yield = (actual / theoretical) x 100
= (2
...
975) x 100
= 31%

Calculating the percentage purity of hydrated copper(II) sulfate:

1
...

3
...

5
...
1 x 12
...
00124
0
...
0062
0
...
2232
(0
...
32%

Percentage yield = (actual yield/theoretical yield) x 100

Theoretical = n = mass/mr = 2/138 = 0
...
0145 x 180 = 2
...
161/2
...
36 x 100 = 236%

Percentage mass = (overall weight / mass of two tablets) x 100
= (0
...
543) x 100
= 11
...
Firstly, the solution is heated in an evaporating basin;
therefore allowing the solvent to evaporate, which leaves a saturated solution
...
The crystals are then collected and dried
...

Filtration - Passing a solid and liquid mixture through filter paper gets rid of the solvent and allows
excess solvent to evaporate
...
The fine, porous material of the filter
paper does not allow the solid, insoluble particles to go through
...


Determining the percentage purity of aspirin:
Titration – To determine the volume that has been consumed when the endpoint (the point at which
the titration is complete) is reached, a calibrated burette must be used to add the titrant
...
It is also when
the solution permanently changes colour; this is due to an indicator
...
This point is identified from the first faint pink colour that persists in
the solution being titrated
...
There is a
slight difference between the change in indicator colour and the actual equivalence point of the
titration
...
It leaves the solid residue behind
...
It isolated the
product
...

Drying – This is carried out to remove water from a compound
...
A desiccator
can also be used to absorb any moisture and keeping the product dry, from the evaporated solvent,
from the surrounding air
...
This is either
done by converting the substance into an insoluble form or by changing the composition of the
solvent to decrease the solubility of the substance in it
...
This cause
solution causing the recordings to be inaccurate, invalid and unreliable
...
This means that you will get an accurate
reading and therefore reduce the error
...
So when adding the sulfuric acid to the measuring cylinder, the bottom of the meniscus must
be on the line
...
This would cause the recordings to be
inaccurate and the experiment to be invalid and unreliable
...
Whilst you are doing this, look at the cylinder at eye-level so you can be sure that you
have added the right amount, once the bottom of the meniscus has fallen on the line
...

Furthermore, an error can also be caused by the misjudgement of the amount of liquid evaporated
on a hotplate
...
If no
crystals were to form, the experiment would not be complete, as you will not be able to work out
the percentage yield of the product
...
To
improve the method before putting the filtrate on the hotplate, pour it into a measuring cylinder
and note the volume down
...
If not, pour it back into the evaporating basin and onto the hot plate and
check the volume again when you think it has reduced enough
...
This means that you will minimise the
error and therefore get a higher percentage yield
...
This means that the recorded mass of the crystals would be less than the actual mass of
the crystals
...
This would cause the recorded percentage yield to be inaccurate
...
By doing this, you can ensure that your
percentage yield would be as high as you can make it
...


Determining the percentage purity of hydrated copper(II) sulfate:
During the titration, one can misjudge the colour of the indicator near the end point - this is the
most common error during this procedure
...
To reduce the percentage
error, a number of people should observe the colour and then come to a final result
...

Another error in the titration could be misreading the volume due to parallax error; this is when
someone reads the volume looking at an angle
...

Parallax error is when we misinterpret a value when measuring something, not looking at it at eyelevel

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