C3.1 Water Testing
Qualitative: this type of analysis shows what type of substance there is in a chemical.
Quantitative: this type measures how much of that substance there is in a chemical
Cations: Positive metal ions
Anions: Negative non metal ions
Test for Cation:
- Flame tests
- Precipitate Reaction
Method of Precipitate Reaction
1) Add drops of sodium hydroxide
2) Precipitate that is formed shows us that one particular ion is present
Aluminium and Calcium both show same precipitates, to differenciate, if there are aluminium ions present and if you add extra sodium hydroxide, it will turn colourless.
C3.2: Safe Water
Halide Ions (anions/non metals) are identified by adding
- adding silver nitrate solution
- dilute nitric acid
- RESULT: Silver Halide precipitate
Test for ammonia:
1) warming it with sodium hydroxide solution
2) smelly alkaline gas given off
3) turns damp litmus paper blue.
C3.5 Water Solutes
Water supply in Britain are obtained from rocks which contain water, this had caused minerals like calcium and magnesium to be dissolved in the water
Concentration: amount of solute dissolved in a given amount of a solvent, measured in milligrams/grams per cubic decimetre (mgdm^-3 or gdm^-3)
Formula to find concentration = amount of solute/volume of solution (g/dm^3)
A consequence of minerals being dissolved in water will be that it will turn the water ''hard'' making it unuseful.
If you mix hard water with soap, it will not form a lather but a precipitate called ''scum'', this is because magnesium and calcium ions combine with soap to form a precipitate.
You have to precipitate all the ions present in the hard water before it can be used, so more soap has to be used.
C3.6 Hard and Soft Water
Water which loses its hardness by heating. The heating effect heats the magnesium and calcium dissolved in the water and forms limescale, which can be removed.
Water which does not lose its hardness when heated and it still forms scum.
Water is passed through an Ion Exchange Column
1) Hardwater Passwed through Ion Exchange Column
2) Ion Exchange Colum contains resins which have weakly attracted sodium ions present.
3) As hard water is passwed through, the sodium ions switch places with the calcium and magnesium ions in the water
C3.9 Preparing Soluble Salts
A base is something that can be reacted with an acid to form water and a base.
Common Method to prepare salts (soluble)
1) Copper Oxide is reacted with Sulfuric Acid
2) Excess Copper Oxide is added to make sure all Sulfuric Acid is used up
3) Copper Sulfate Solution is formed, excess Copper Oxide is filtered.
4) Copper Oxide becomes the filtrate
5) Copper Sulfate Solution is collecrec and left to evaporate
6) Copper Sulfate crystals form because water has been evaporated.
Copper Oxide + Sulfuric Acid -----> Copper Sulfate + Water
C3.10 Preparing Soluble Salts (2)
1) Fill conical flask with alkali with a pipette a pippete filler, with 3 drops of indicator
2) Fill burette with acid
3) Add acid to alkali eith burette
4)The indicator added to alkali will change colour, this shows all the alkali has been reacted
5) Repeat it 2 more times
Once the repeating is finished, the mean volume of acid added to react the measured amount of base solution, all the acid will and only salt and water will remain.
Phemnolphthalien: for weak acids and strong alkali
Methyl Orange: for strong acids and weak alkali