Pipetting and Buretting Quantitative techniques
Science
Question 1 –
A student completed the same experiment and achieved the following results:
Mean volume delivered: 24.93 mL
Mean deviation: ± 0.13 mL
The pipette they used was a 25.00 mL pipette, with a manufacturer’s mean deviation claim of ± 0.06 mL.
a) Is mean deviation a measure of accuracy or precision? i.e. does the mean deviation reflect how far the result is from the true value (accuracy) or how far the values are from each other (precision)?
b) Comment on this student’s results with respect to accuracy and precision.
Question 2 – Titration
a) Will the concentration of the sulphuric acid, H2SO4, in the conical flask (receiving vessel) be the same as that of the sample in the beaker that you collected from the servery? Does this matter? Why/Why not?
b) Calculate a mean (average) value for the titre values you have chosen. Justify any exclusions you have made.
c) The equation for the acid-base neutralisation reaction you perform in each titration is given below. Balance this equation. H2SO4(aq) + NaOH(aq) ⇋ Na2SO4(aq) + H2O(l)
e) The ratio of the number of moles of H2SO4 to NaOH required for reaction (nacid:nbase) is given by the balanced equation. Using your balanced equation and the value of number of moles of NaOH you have just calculated (number of moles = 6.85), what is the number of moles of H2SO4 in the conical flask? f) Rearrange the equation n = cxV to calculate the concentration of your H2SO4 solution. g) Obtain the true value from the servery and compare this to your own experimentally determined concentration.
