How do you find the hardness of a given water sample without using EDTA?

Answer 1

mention the salts causing temporary and permaneat hardness

Answer 2

Assumptions during this experimentMagnesium(II) ions are not present in the selected water sample, as if it does exist, it behaves almost as Calcium(II) ions. ProcedureStep 1

Dilute 10.00 cm3 of water sample to 200cm3 in a beaker. Add Methyl Red indicator.

• Dilution: To have adequate volume of water to a boiling process
• The solution is red in colour.

Step 2

Boil the solution and add very slowly a warm solution of ammonium oxalate.

• Slow addition: As ammonium oxalate is a volatile compound, fast addition may cause decomposition.

Step 3

Add the resultant hot solution dilute (1:1) ammonia solution drop wise and with stirring until the mixture is neutral or slightly alkaline.

• The appropriate volume is recognized by the indicator colour change.
• Drop wise: Excess ammonia will make the medium alkaline.
• Stirring: To spread ammonia evenly in the solution and to maintain the even temperature in the solution.

Step 4

Allow the solution to stand without further heating for at least 1/2 hours.

• As it takes time to deposit the entire precipitate
• The precipitate is CaC2O4.

Step 5

Filter through an ordinary filter paper.

Step 6

Wash the precipitate with cold 0.1 - 0.2 % ammonium oxalate solution at least five times.

• It makes the CaCl2 left in the precipitate CaC2O4.
• It is verified by the test to the Chloride ion. (dil. HNO3 + AgNO3)
• If those remained as CaCl2, it would not be counted in the titration and give an error value.

Step 7

Wash the precipitate with distilled water.

• It removes the ammonium oxalate on the surface of the precipitate.

Step 8

Transfer the precipitate into a beaker using sulphuric acid and distilled water.

• Sulphuric acid: It gives acidic medium which would not interfere in the titration.

Step 9

Heat the solution and titrate with 0.02 mol dm-3 KMnO4.

• Heating: To give the activation energy.

Titration Reaction16 H+(aq) + 5 C2O42-(aq) + 2 MnO4-(aq) --> 10 CO2(g) + 2 Mn2+(aq) + 8 H2O(l)

Indicator colour change: Colourless to pale pink.

CalculationsFrom the average burette reading, the amount of oxalate ions can be found. It is equal to the Calcium(II) ions in the titration flask. It is same as in the 10.00 ml water sample. As we can calculate the mass of the Calcium (II) ions in a known volume of water, the calcium level could be calculated for the particular water source.