EXERCISE 1 - Performing (Repetitive) Calculations

In an experiment, a 2.50M stock solution (using a 10ml pipette and 50ml volumetric flasks) was sequentially diluted by a factor of five to generate a series of five diluted solutions. i.e. Solution 1 was made by pipetting 10ml of Stock to a 50ml volumetric flask and making up to 50ml with deionised water. Solution 2 was made by pipetting 10ml of Solution 1 to a 50ml volumetric flask and making up to 50ml etc. The pipette error was estimated as ±0.1ml, the error in the stock was known to be ±0.02M and the errors in the volumetric flasks were assumed to be negligible.

Calculate the concentrations of the five solutions with their associated errors.

Open a new Excel workbook and enter following data:

The general formulas for this calculation are:

Calculate the concentrations of C_New, C_New,Max, C_New,Min and determine the associated error s_C,New of all five solutions.

You should get results for Row 1 as follows:

If your results do not agree then follow these instructions.

Now you can extend the calculation for the remaining solutions. The numbers in the D, E & F columns will be the same for all the calculations, so highlight D2, E2 & F2 and copy them down to Row 6. Similarly, the formulae used to calculate the concentrations and errors are the same (just with different numbers), so also copy G2, H2, I2 & J2 down to Row 6. Finally copy B3 & C3 down to Row 6.

For Row 3 you should get the following results:

If your results do not agree then follow these instructions.

To get to the next exercise, select the right answer. The concentration of Solution 5 (in Row 6) in mM with associated error is:

(4.00± 0.05)mM        (0.80 ± 0.04)mM       

(0.80 ± 0.05)mM        (0.40 ± 0.04)mM       

Go back to Introduction section.