Saturday, May 31, 2008

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..

Chapter 8 Chemistry Salt

normally people get confused with this chapter so I m going to provide all information regarding this chapter.. Happy Reading ^^

-All nitrate salts are soluble in water
-All ammonium salts are soluble in water
-All sulphate salts are soluble in water except barium sulphate,lead(II) sulphate,calcium sulphate.
-All chlorides are soluble in water except lead chloride,silver chloride,mercury chloride
-All carbonates are not soluble in water except sodium carbonate,potassium carbonate and ammonium carbonate.
-Salt containing Sodium , potassium and ammonium are all soluble in water.

This is the important things you all have to know...the basic actually.

Next,

For sodium salts,potassium salts and ammonium salts.(PAS)
To obtain it..
We have to use titration method.
taking an Acid + with sodium hydroxide/potassium hydroxide/ammonium Alkali then we will get the same (PAS) salts..
Water will be produced at the end of experiment.
They also will ask..
How u know the reaction has completed?
Using an indicator like universal indicator/methyl orange/phenolphthalein

Pink to colourless for phneolphthalein
Yellow to orange for Methyl orange

The end-point is determined when the colour changes to (write ur answer based on indicator used)

After the neutralisation process is carried out..
Crystallisation is carried out to obtain pure salt..
Generally,when titration method is carried out..
The alkali must be in the conical flask whereas the acid in the burette..
Ever wonder why?
Because alkali cannot pass through the small hole of burette opening..
It's nature..i guess it's too soapy.
So remember put alkali at the bottom !!

The other experiment is recrystallisation process..

Aim:To get a pure form of copper(II) sulphate.

Hypothesis:A purer form of copper sulphate can be obtained by recrystallisation.

Manipulated variable:impure copper(II) sulphate
Responding variable:Purer copper(II) sulphate
Constant variable: Water

Procedure:
1)Impure copper(II) sulphate crystal are dissolved in distilled water.
2)The solution is heated so as to evaporate some of the water in the solution.This is to make the solution more concentrated.
3)The saturated solution is left to cool.This is to enable crystallisation to occur.
4)The purer copper(II) sulphate crystals are seperated by filtering.They are then washed with distilled water.
5)The wet crystals are then dried by pressing them between two pieces of filter paper.

Conclusion:The crystals obtained are clearer and more bluish than the original crystals.These crystals are purer copper(II) sulphate crystals.

Chemistry Chapter 8 Salt important experiment.

Chapter 8 salt is among the most popular chapter in SPM chemistry..
There's no doubt..You have to memorise the colour changes and experiments..

Alright..this experiment is important and should be memorised for the sake of exam.

(Preparation of Magnesium Sulphate) ->prepare a salt...
this salt is obtained from Acid + Metal Oxide..

MgO+H2SO4 -> MgSO4+H2O

1)50cm3of 1.0moldm-3 of sulphuric acid is measured and poured into a small beaker.
2)The sulphuric acid in the beaker is heated as shown in the diagram.(refer to book the diagram)
3)Magnesium Oxide is added in excess into the small beaker and stirred.
4)The hot mixture is filtered to remove excess magnesium oxide.
5)The filtrate is transfered into an evaporating dish and heated until1/3 of it's original volume.
6)The solution is allowed to cool and crystallize in the crucible.
(crystallization is a process where pure salt in crystal form is formed)
in short free from impurities..
7)The crystal obtained are dried by placing it between two filter papers.

EST essay

Benefits of recycling
-how aluminium cans can be recycled.

Hmm..the format I m not very sure..
If I am wrong please correct them for me.

Recycling Aluminium Cans (then underline)

Aluminium cans are made from bauxite.Bauxite,like all other minerals,has to be mined. This process is not only dirty, it is also expensive. Energy, in the form of heat, is required to make aluminium cans from bauxite. Now, we can save much of this energy and cut down pollution because of recycling.Recycling aluminium cans is a relatively simple process.

Firstly,used cans are collected by the many cash-for-cans centres that are mushrooming all over the country.Here, the cans are sorted. Cans which are in bad shape and are considered useless are discarded while the rest are sent to the recycling factory. As soon the cans reach the recycling factory, they are sent to a magnetic head which seperates aluminium cans from steel cans. Steel cans stick to the magnetic head, whereas aluminium cans do not. The steel cans are rejected. The aluminium cans are crushed into blocks. In the smelter or furnace, high temperatures melt the blocks of aluminium. The molten aluminium is then poured into casting moulds and cast into ingots.

When these ingots are passed through rollers, they become aluminium sheets. The aluminium sheets are then cut to the required size and rolled into new cans. The cans which are now ready for use are then sent to drink manufacturers.

Report by: (date at the right-hand side)--> 1/6/08

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