To Determine the Concentration of Limewater

Method:

Diluting:

1. Rinse the volumetric pipette, flask and stopper, a 100cm3 beaker, funnel and teat pipette with distilled water.
2. Rinse 100cm3 beaker with HCl and pour into a labelled waste beaker. Pour fresh acid into 100cm3 beaker and label it “undiluted acid”.
3. Rinse the volumetric pipette with 10cm3 of HCl and discard to waste beaker.
4. Use pipette to accurately measure 10cm3 of HCl into the 1dm3 volumetric flask.
5. Add distilled water in a wash bottle to the acid until the level has almost reached the white line, then use a teat pipette to fill it up to the point where the meniscus is just on the line.
6. Insert stopper and invert flask to ensure complete mixing.
7. Label the flask “0.02 mol dm-3 HCl”.

Standardising:

1. Rinse burette with distilled water and then with a little of the dilute HCl solution.
2. Drain burette into your waste beaker and fill it with acid.
3. Wash pipette with distilled water and with a full 10cm3 of Ca(OH)2 solution.
4. Discharge into your waste beaker.
5. Rinse the conical flasks with distilled water and drain them.
6. Pipette exactly 10cm3 of Ca(OH)2 into one flask.
7. The burette should be adjusted to a volume which is easily read, and the initial volume is recorded.
8. Add 2-3 drops of methyl orange indicator solution to the Ca(OH)2 in the conical flask.
9. Add the acid from the burette to the flask, with swirling, about 1cm3 at a time, until the indicator changes colour from orange to pink.
10. Note down your reading. Your titre is derived from the difference in the two readings.
11. Repeat the procedure.
12. Carry out titrations until you have at least 2 results which agree to ±0.1cm3.

Dilution calculation:

We need a titre which isn’t too large as to not be able to fit in a 100cm3 burette, and not too small as to make the measurement highly inaccurate with large % errors.

Bibliography:

Chemistry experiment sheet 12E4