JC1 Science Practical Assessment (1) hints:

Note : This JC1 SPA hint (not really a true practice) is very easy and your JC’s SPA should be much more difficult. It is just used to illustrate SPA practices. The actual SPA questions and style differ markedly from this practice. You may wanna grab hold of HCI, VJC and RJC and other JCs SPA packages for great references!

Question

You are required to find the percentage purity of a sample of sodium carbonate, Na2CO3, by the following method.

FA1 is a solution containing 4.00 g dm-3 of the impure sodium carbonate.

FA2 is a solution of hydrochloric acid, HCl, of concentration 1.00 mol dm-3.

Dilution of FA2

By using a burette, place between 20.00 cm3 and 22.00 cm3 of FA2 into a 250 cm3

graduated flask.

Final burette reading / cm3

Initial burette reading / cm3

Volume of FA2 used / cm3

[2]

Make up the contents of the flask to the mark with distilled water and label this solution FA3.

Pipette 25.0 cm3 of FA1 into a conical flask. Add a few drops of methyl orange and titrate with FA3 from a burette.

Repeat the titration as many times as you think necessary to obtain accurate results.

1

Titration of FA1 with FA3

Rough Accurate

Final burette reading / cm3

Initial burette reading / cm3

Volume of FA3 used / cm3

Cross out the word 'Rough' if you regard that titration to be accurate.

Summary

25.0 cm3 of FA1 required cm3 of FA3 for neutralisation.

Show which results you used to obtain this value of the volume of FA3 by placing a tick ( ) under the readings used.

[13]

Calculations

(a) Calculate how many moles of HCl there are in the 250 cm3 graduated flask.

[1]

(b) Calculate how many moles of HCl there are in the volume of FA3 required to react with 25.0 cm3 of FA1.

[1]

2

(c) The equation for the complete reaction of HCl with Na2CO3 is

Na2CO3 + 2HCl 2NaCl + CO2 + H2O

Calculate how many moles of Na2CO3 there are in 1.00 dm3 of FA1.

[1]

(d) Calculate the mass of Na2CO3 in 1.00 dm3 of FA1.(Relative atomic masses: C, 12.0; O, 16.0; Na, 23.0)

[1]

(e) Calculate the percentage purity of Na2CO3.

[1]

3