Chemistry - Controlled Assessment P2 Flashcards
Was the resolution of measuring equipment appropriate?
Equipment, resolution and units, appropriateness
The burette had a resolution of 0.05 cm3 which was appropriate as it was enough to be able to identify a difference between the results collected however a pattern could still be identified. Perhaps an even smaller resolution may have perhaps helped improve the results to find concordant results.
What was the range of the independent variable and was it appropriate?
IDV: volume of alkali solution
Range: 10 cm3 to 40 cm3
The range enabled me to identify a pattern which helped prove the hypothesis.
What were the difficulties, what effect did they have and how were they solved?
Incorrectly filling/measuring the burette - gives incorrect value for volume of acid used - measure from eye level and refill carefully
Leaving funnel in burette - drops falling into burette mean more acid is added than expected - remove funnel each time
Swirling - don’t wait long enough for the alkali and acid to react - use magnetic stirer
Accurate volume of alkali with measuring cylinder - too much/little will affect the volume of acid needed - use volumetric pipette
Determine when neutral using the phenolphthalein indicator - can’t see when the solution turns colourless - use white paper behind the solution to see end clearer.
Did your results support the hypothesis?
Yes/no, reference to pattern, data
Yes, our results do support the hypothesis as we see that, as the volume of NaOH increases, the volume of HCl necessary to neutralise the solution e.g. At 10 cm3 of NaOH, 10.65 cm3 of HCl was needed whereas at 40 cm3 of NaOH, 45.5 cm3 of HCl was required for the solution to neutralise, showing a positive relationship.
Did you have any anomalies?
No, all of our results fit the pattern which was a positive, non-linear relationship. All points were close to the line of best fit.
Yes
Identify anomalie
What’s its value?
Say that it doesn’t fit the pattern and line of best fit
No
Say all values follow the pattern and are close to the line of best fit
What’s the pattern
How do you draw a sketch graph?
Label the axis with units and draw a line - a scale isn’t necessary.
Do case study 1, 2 and 3 support the hypothesis?
Explain a simple statement about whether it is supporting the hypothesis or not.
Detailed description of pattern which each one shows. State if the IDV is different.
Use examples of data from each c.s. And describe any anomalies.
E.g. Yes C.S. 2 supports the hypothesis as it shows that, as he volume of NaOH increases, the average volume of HCl increases. It is also more accurate than 1 as it has repetitions however, at 40 cm3 NaOH for trial 2, the acid recorded was 31 cm3 which is an anomaly. But we see this proves he hypothesis as, at 10 cm3 the average volume of HCl was 5.3 cm3 whereas at 50 cm3 it was 25.6 cm3
Case study 4 example: Do the results of C.S. 4 support the students conclusion?
Qualitative comments: We don't know/must consider - The activity the students have done The sample size Their diet Could be a placebo effect Whether or not they already had indigestion Have they had any other drinks Gender Age
Quantitative:
Initially we would agree that it supports their hypothesis as, on week 1, 19 students who had orange juice had indigestion whereas 15 people who had water had indigestion. However, by week 4, 5 students had indigestion for both orange juice and water and we don’t know about the students’ diets, activity etc.
Overall, the pattern shows that there are generally more students with indigestion who had orange juice compared to water however, perhaps if this was repeated or continued for longer than a month, we would be able to see a clearer pattern.
Does your hypothesis and results relate to the context.
Yes, our results relate to the context as they show that when we increase the volume acid, we need to increase the volume of acid added in order to neutralise the solution therefore, if the farmers’ fields are acidic, the more acidic they are, the more alkali is necessary to neutralise the fields.
insert data from experiment
This would be useful to farmers as they can use our results to help calculate the volume of alkali they need in order to neutralise their fields yet prevent waste, save money and collect maximum yield.
How do you calculate the mean?
Don’t include anomalous results
Must match the original data
