Unit 2: Practical Scientific Procedures and Techniques.
Learning aim, A: Undertake titration to determine the concentration of a solution.
Aim of the assessment- The aim of this assessment is to find the exact concentration of an unknown
sample of sodium hydroxide (NaOH). To do this find the concentration of hydrochloric acid that you are
going to be titrating the HCl against a standard solution of sodium carbonate.
Calibrating a balance-
Equipment needed.
1. Balance
2. Masses- 10g, 20g, 30g, 40g and 50g
Method P1, P2,M1
1. Turn on the balance and leave the device for a satisfactory amount of time to allow it to reach a
thermal equilibrium (approximately a minute).
2. Add a known mass of 10g to the balance.
3. Record the mass and repeat this step three times.
4. When you record each of the values calculate the average. This can be done by adding the values of
each mass together and then dividing them by the number of values there are (excluding the
anomalies).
5. For example, 10.07 + 10.07 + 10.07 = 30.21, 32.1/ 3 = 10.07.
6. Repeat steps 2-5 using masses of 20g, 30g, 40g and 50g.
7. Record the results in a table like the one below.
Calibrating a balance result
Known Measured masses on a balance(g)
, masses. 1st (g) 2nd (g) 3rd (g) Average(g) (2d.
(g) p)
10 10.07 10.07 10.07 10.07
20 20.04 20.03 20.03 20.03
30 30.10 30.09 30.09 30.13
40 40.24 40.24 40.24 40.24
50 50.32 50.32 50.32 50.32
Average of the masses
The average of these masses shows that the balance has been calibrated correctly as the values are close
together. This shows that they are accurate increasing the reliability of the results when the material is
weighed out.
Problems that occurred during the experiment
There were some limitations when weighing the 20 and the 30 kg masses. The 20 kg mass weighed 20.04
then 20.03and then 20.03. Then the 30 kg mass weighed had the same problem. The first measurement
weighed 0.01 more than the second two. However, this is down to human error and there for cannot be
avoided.
Accuracy, precision, and reliability
Accuracy- The results were close to benchmark. This is because the results were not more or less than 0.01
away from the exact value.
Precision- The results were precise as the repeat measurements were either the same or very near each
other. For example, 20.04 and 20.03 are 0.01 away from each other.
Reliability- The results were reliable as close together.
, Hazards, risks, and prevention
There were no hazards in this experiment. However, the masses could have fallen and caused damage to
the lower half of the body. This can be prevented by placing the balance on the middle of the table.
Improving the experiment D1
The experiment could be improved by using a balance that can weigh more decimal places. This would
prevent any errors from occurring.
Calibration of a volumetric pipette
The maximum for the volumetric pipette is 25cm3.
Equipment needed.
1. Beaker (50ml)
2. Pipette (25cm3)
3. Distilled water
4. Balance
P1, P2, M1
Method
1. Place a clean dry beaker on the balance and then proceed to zero the balance to eliminate the mass
of the beaker.
2. Suck up distilled water into the pipette so that the bottom of the meniscus sets on the 25cm 3 line.
3. Carefully dry the tip of the volumetric pipette with a paper towel to make sure no drips enter the
beaker. Ensure that you do this step carefully as the tip of the volumetric pipette is fragile.
4. Transfer your distilled water into the beaker from the pipette and then proceed to weigh.
5. Place your beaker on a ‘zeroed’ balance and record the mass. Mine was 44.07g.
6. By using the mass from the distilled water, we can find the volume.
Learning aim, A: Undertake titration to determine the concentration of a solution.
Aim of the assessment- The aim of this assessment is to find the exact concentration of an unknown
sample of sodium hydroxide (NaOH). To do this find the concentration of hydrochloric acid that you are
going to be titrating the HCl against a standard solution of sodium carbonate.
Calibrating a balance-
Equipment needed.
1. Balance
2. Masses- 10g, 20g, 30g, 40g and 50g
Method P1, P2,M1
1. Turn on the balance and leave the device for a satisfactory amount of time to allow it to reach a
thermal equilibrium (approximately a minute).
2. Add a known mass of 10g to the balance.
3. Record the mass and repeat this step three times.
4. When you record each of the values calculate the average. This can be done by adding the values of
each mass together and then dividing them by the number of values there are (excluding the
anomalies).
5. For example, 10.07 + 10.07 + 10.07 = 30.21, 32.1/ 3 = 10.07.
6. Repeat steps 2-5 using masses of 20g, 30g, 40g and 50g.
7. Record the results in a table like the one below.
Calibrating a balance result
Known Measured masses on a balance(g)
, masses. 1st (g) 2nd (g) 3rd (g) Average(g) (2d.
(g) p)
10 10.07 10.07 10.07 10.07
20 20.04 20.03 20.03 20.03
30 30.10 30.09 30.09 30.13
40 40.24 40.24 40.24 40.24
50 50.32 50.32 50.32 50.32
Average of the masses
The average of these masses shows that the balance has been calibrated correctly as the values are close
together. This shows that they are accurate increasing the reliability of the results when the material is
weighed out.
Problems that occurred during the experiment
There were some limitations when weighing the 20 and the 30 kg masses. The 20 kg mass weighed 20.04
then 20.03and then 20.03. Then the 30 kg mass weighed had the same problem. The first measurement
weighed 0.01 more than the second two. However, this is down to human error and there for cannot be
avoided.
Accuracy, precision, and reliability
Accuracy- The results were close to benchmark. This is because the results were not more or less than 0.01
away from the exact value.
Precision- The results were precise as the repeat measurements were either the same or very near each
other. For example, 20.04 and 20.03 are 0.01 away from each other.
Reliability- The results were reliable as close together.
, Hazards, risks, and prevention
There were no hazards in this experiment. However, the masses could have fallen and caused damage to
the lower half of the body. This can be prevented by placing the balance on the middle of the table.
Improving the experiment D1
The experiment could be improved by using a balance that can weigh more decimal places. This would
prevent any errors from occurring.
Calibration of a volumetric pipette
The maximum for the volumetric pipette is 25cm3.
Equipment needed.
1. Beaker (50ml)
2. Pipette (25cm3)
3. Distilled water
4. Balance
P1, P2, M1
Method
1. Place a clean dry beaker on the balance and then proceed to zero the balance to eliminate the mass
of the beaker.
2. Suck up distilled water into the pipette so that the bottom of the meniscus sets on the 25cm 3 line.
3. Carefully dry the tip of the volumetric pipette with a paper towel to make sure no drips enter the
beaker. Ensure that you do this step carefully as the tip of the volumetric pipette is fragile.
4. Transfer your distilled water into the beaker from the pipette and then proceed to weigh.
5. Place your beaker on a ‘zeroed’ balance and record the mass. Mine was 44.07g.
6. By using the mass from the distilled water, we can find the volume.
