My friends and I did it together, we also looked over it with a science teacher with a degree in chemistry and she said it was worthy of a distinction. PS: Don't copy word for word ;)
D3
In this essay I am going to be evaluating the instruments and discussing why these
instruments are appropriate to use and evaluate how accurate the measurements
and subsequent results are. Also, suggesting more appropriate alternatives.
pH experiment
When carrying out this experiment, we calibrated a pH meter with a buffer solution
and then used the pH meter to measure the pH of unknown samples. A pH meter is
a glass electrode combination used to measure the pH of a solution accurately,
indicating its acidity or alkalinity. In this experiment, in order to calibrate it we had
to dip it into three buffer solutions with different pH. During this process there was
room for error. Although, after each time we dip the pH meter into a buffer solution
we are supposed to rinse it with water. Because the electrode is very sensitive, if
the electrode is not rinsed properly it may lead to impurities because a little from
the previous buffer solution it was used on will enter the next buffer solution. After
dipping the electrode into a buffer solution, we had to wait for the reading to
stabilize, but most if the time, the reading never stabilized and it continued to
increase and decrease randomly. This can lead to inaccurate results. Also touching
the glass bulb at the end of the electrode can cause impurity, affecting the final
results. A pH meter is the best instrument to use to test pH of a solution because
unlike the normal indicator, it displays numerical data which is more accurate than
colour change on a piece of paper. From looking at the results we obtained, some
pH values from both samples were not consistent with the class average pH value
for each sample. In the results Table we noticed that a group had measure their
sample A to have a pH value of 4.4 which was very far off from the class average
and even compared to other group results. This value was regarded as an anomaly
and was not used in calculations. This inaccurate data was caused by an error, a
faulty pH meter, uncalibrated pH meter or impurities caused by cross contamination
of buffer solutions. A better method that may have led to better results is to
different calibrated pH meters to reduce risk of cross contamination when trying to
clean the pH meter.
Colorimeter experiment
In this experiment, we had to dilute the reference solution with distilled water to
make the solution labeled 1 to 6 in a table on the sheet. To do this, we used
measuring cylinders, conical flasks and dropping pipettes. For this procedure, we
made sure we labeled each conical flask we kept our reference solution into, we also
labeled the measuring cylinder to avoid mixing up solutions. This helped to reduce
any risk of errors. The scale of the measuring cylinder we used was the appropriate
one for this procedure. For this experiment we used a colorimeter to determine the
concentration of Cu (ii) solution by measuring the intensity of the colour. This
instrument was very reliable because it gave highly accurate results as it able to
identify when more light was absorbed by measuring the difference between the
amount of light at its origin and that after passing the solution.
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