Unit 2 - Practical Scientific Procedures and Techniques
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unit 2 - Aim A - Titration
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Unit 2 - Practical Scientific Procedures and Techniques
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PEARSON (PEARSON)
This is an in depth assessment discussing the processes of titration and colorimetry to determine the concentration of solutions. It includes lists of laboratory equipment and their calibrations, preparation of solutions using titration and colorimetry.
Unit 2 - Practical Scientific Procedures and Techniques
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Titration – Unit 2 – Aim A: undertake titration and colorimetry to determine the concentration of solutions.
Calibration:
Before any experiments are carried out, there needs to be a calibration of the equipment to make sure the
results are accurate and effective. Over time equipment can change and drift which results in inaccurate
readings so they must be calibrated before every use. Calibration means adjusting or standardizing your
equipment so it can be more precise (SensoScientific, 2019)
Pipette calibration:
Starting with the pipette used in titration. To calibrate a pipette, you will need a 25ml pipette, distilled water,
two beakers, a weighing scale, and a pipette filler.
- First make sure that the balance in placed firmly and flat on the table.
- Take a clean dry beaker and place it on the centre of the balance.
- Make sure to zero/tare the scale so that the reading when the beaker is on the scale reads
0.00
- On the pipette filler there are 3 buttons, A, S and E. A stands for air out of ball, S stands for
sucking up the solution and E stands for empty. Squeeze letter A to get the air out of the ball
then place onto the end of the pipette.
- Place the pipette in the distilled water being careful not to touch the bottom of the beaker as
it can crack the glass.
- Using the pipette filler, pressing S, draw up into the pipette until the bottom of the meniscus
is on the graduated line, checking at eye level for accuracy
- Transfer the water from the pipette into the dry beaker on the balance. Pressing E to empty
the water.
- The reading off mass of water should be 25g, the same as the pipette, when we did our
experiment, it read 24.92g so a very close value showing the accuracy of the equipment and
the calibration was done correctly
- Reasons why the result is not exactly the same is because some drops of water could have
been spilled or stayed in the pipette
- As well as this the room temperature needs to be taken into consideration, at the time the
experiment was done the room temperature read 25ºC.
- The pipette is now calibrated
pH meter calibration:
To calibrate a pH meter, you need a pH meter, one beaker filled with a buffer solution of pH 4.0 and another
filled with another buffer solution of pH 9.0, and another beaker with clean distilled water. Place the pH meter
in the beaker full of buffer solution 4.0. The pH meter should read 4.0 this is how you know that the equipment
is accurate. Take the pH meter out of the buffer solution and place it in the beaker full of distilled water to
wash it off. Then take the meter out of the water and place it in the other beaker with a buffer solution of 9.0.
again, this should read 9.0. If the results are not 4.0 or 9.0 or not close at all then the equipment is not
accurate so you must use another or new one.
, Weighing balance calibration (2 or 4 dp):
To calibrate a weighing balance, you will need a range of different known weights which are kept in their
original case and protected from airborne contaminants to avoid them changing weight. So, when handling
them use tweezers or gloves to avoid getting any water, oil, or dirt from your hands, which could affect their
weight. To start the experiment, you will need to put the weighing balance flat on the table making sure it is
flat and level. Make sure the scale reads 0.00 or 0.000. starting with the 1g weight place is on the scale (using
tweezers or gloves), the scale should read 1.0g if it doesn’t then your scale is inaccurate. Repeat this
calibration with other known weights of 2g, 5g and 10g. The scale should read 2g, 5g and 10g. The calibration
for a weighing balance is done and the known weights should be placed back into their original case and
locked away.
1 - Making a standard solution -
Introduction:
The first experiment we carried out is making a standard solution. Making a standard solution allows you to
find the solutions used in qualitative practical. The standard solution made will then be used for the next
experiment where we are going to titrate it with hydrochloric acid, to work out the concentration.
Equipment:
Volumetric flask (25ml)
Weighing balance
Weighing boat
Distilled water in a bottle
Sodium carbonate (Na2CO3)
Funnel
Beaker
Spatula
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