How do I identify unknown solutions?

Question

Identifying Unknown Solutions

You will be provided with the following solutions labelled with a letter only: (0.1 mol/L NaOH, 0.1 mol/L NaCl, 0.1 mol/L Ch3COOH, 0.1 mol/L HCl, 0.1 mol/L H2SO4, 0.1 mol/L H2O.

You must devise a method to identify each of the solutions.

The chemicals available will be methyl orange indicator, phenolphthalein indicator, sodium carbonate, solutions of silver nitrate, barium nitrate, sodium sulfate and ammonia. You may not need all of these solutions.

Anyone have any idea what I should do?

So far, I know how to separate them into acids and bases but I don’t know how to determine their pH.

Answer 1

nice payal.

Answer 2

You have got :

1 sample NaOH alkaline

2 samples, NaCl and water - neutral

1 sample CH3COOH weak acid

2 samples HCl and H2SO4 strong acids.

Step 1: 1 drop phenolphthaleion into each tube. 1 will turn pink - mark as NaOH

Step 2 : 1 drop methyl orange into the remaining 5 tubes: 2 will turn red, the others orang/yellow

Step 3 Take the two red tubes - red is acid- add drop of AgNO3 into both. White precipitate indicates chloride, Mark as HCl

Step 4 you can be sure that the other tube is H2SO4, but to make sure, add barium nitrate, white ppt confirms sulphate, mark as H2SO4

You have now identified 3 of the 6, leaving only NaCl, CH3COOH and water.

Step 5: add drop AgNO3 to the tubes, white ppt indicates chloride, mark as NaCl

You now have water and CH3COOH left.

You now have to differentiate between the CH3COOH, a weak acid and water. You could possibly smell the acid (vinegar) but I am sure that your tutor won't accept this.

Step 6: I propose adding a drop (no more) of ammonia to both tubes. The water should experience a pH rise which will turn the already present methyl orange indicator a distinct yellow, but the tube containing the CH3COOH will remain acidic (orange/red colour )because the acid has neutralised the base and pH has not gone up.

Mark the tubes accordingly. You have now identified the contents of the 6 tubes.