Chapter 8 Salt (part 2)

Continuous Variation Method.
This method is used to construct an ionic equation.

The Steps:
1) A fixed volume of solution P reacts with increasing volume of solution Q.
(Normally solution P is Potassium Chromate,whereas Q is Barium Chloride)
2)After the experiment,the number of moles of P and Q are calculated.
3)The ratio of P:Q is calculated.
4)Ionic equation and empirical formula of the compound are determined.

Hypothesis:
The height of the precipitate increases to a maximum height when barium chloride is continuously added to potassium chromate(VI).

Procedure:
1)Two clean burettes are cleaned and fixed onto a retort stand
2)To the first burette is filled 0.5moldm-3 of potassium chromate(VI).To the second burette is filled with 0.5moldm-3 of barium chloride.
3)Eight test tubes are labelled from 1 to 8 and placed on a test tube rack.
4)Each test tube is filled with 5cm3 of potassium chromate from the 1st burette.
5)Barium chloride from the second burette is then added to each test tube according to the volume as shown in table.
6)The mixture
in each test tube is then shaken and left to settle for 20minutes.
7)The height of the precipitate in each test tube is then measured with a ruler.
8)The results are recorded in table.

Discussion:
After the reaction,the solutions in 1st test tube to 4th remain yellow.This is because they contain an excess of potassium chromate.
From the 5th test tube of the 8th test-tube,all the potassium chromate would have reacted.
Thus,the solutions in all the test tube will be colourless.All these solutions contain an excess of barium chloride which is colourless.
Hmm..
(personal explanation)
The bottom of the test tube will be barium chromate..which have a constant height starting from test tube 5..then the top will be excess barium chloride which is added continuously for 1cm3 for each test tube until the 8th test tube.
yeah..before i forget..the potassium chloride formed will also be colourless at the top of the test tube.Hence,barium chloride and potassium chloride will be at the top of it..