Week 2
ERROR ANALYSIS AND GRAVIMETRY ANALYSIS
Data Handling, Errors and Statistics in Analytical Chemistry

On Week 2, We learned mostly about calibration and statistics calculations.

Firstly, we were given a situation on how to calibrate a pipette.

Below is the steps to calibrate a 10mL pipette with some notes I have taken down during the lecture.

Important notes: 

• Temperature must always be taken into account when determining the density of water as it will always change according to the temperature.
• Always keep the decimal places throughout the calculations as it is. Only change the final answer as 2 d.p.

Next, we can calibrate the 10mL Pipette by using 50 measurements.

Based on this given example, there is 0 out of 50 measurements that has the value of ‘10.000mL’, this indicates that no matter how careful one carries out the experiment, there will always be random errors, which affects the precision.
 

Next, we learn to find the mean, mode, median, standard deviation, max & min value, and spread using MS Excel.

Mean: Average (=average(e4:e20,h4:h20,......))

Mode: Most repeated number

Median: The middle value of arranged numbers (=median(e4:e20,h4:h20,......))

Spread: range of data (max-min)

Standard Deviation: 

• How much the value differs from the true mean value/how precise is your data (=stdev.s(e4:e20,h4:h20,......))
• Both equations for population/sample gives almost the same answer but sample standard deviation equation is commonly used.

Then, we learned about the Normal Distribution Curve which is also known as Bell Curve/Gaussian Curve.

The Gaussian Curve represents the precision.

The standard deviation for the above experiment is very low, 0.025 which represents high accuracy.

Coming up next is the Confidence interval (CI).

Based on the normal distribution curve and confidence level table above, when the Confidence level is at 50%, the z value is 0.67.
 

Exercise:

i)Determine the 80% Confidence Interval (CI) for 1122mg/ L and s.d. is. 19?ii)Determine the 95% Confidence Interval (CI) for 8 measurements, given mean value is 1100.6mg/ L and s.d. is. 19?

When we increase the no. of measurements, the value of +- will be smaller, which increases the precision.
 

Grubbs Test and Q-test is used to decide whether a value should be discarded or not (outlier).

When the Gcalculated>Gtable, the value is discarded.
When the Gcalculated<Gtable, the value is kept.

When the Qcalculated>Qcritical, the value is discarded.
When the Qcalculated<Qcritical, the value is kept.

Mentimeter Quiz:
What is the function of the desiccator?
Ans: To keep sample dry

Based on Wikipedia, desiccators are sealable enclosures containing desiccants used for preserving moisture-sensitive items such as cobalt chloride paper for another use. A common use for desiccators is to protect chemicals which are hygroscopic or which react with water from humidity.