qualatitive analysis

Question 1

What is the test for carbonates?

Answer 1

Add nitric acid. If you see effervescence, it COULD contain a carbonate as a gas is
produced.
Bubble this gas through limewater. If cloudy then gas was CO2 and thus carbonate was present.

Question 2

Give the test for sulfate ions

Answer 2

Add nitric acid to dissolve any carbonates to prevent the formation of BaCO3 precipitate (aka a false positive which can mask desired observations).
Add barium nitrate solution (or anything with Ba2+).
If white ppt forms, you have a sulfate present.
This is because BaSO4 forms

Question 3

Give the test for halides with a precaution

Answer 3

1. Add nitric acid to dissolve any carbonates to prevent the formation of Ag2CO3 precipitate
   (aka a false positive which can mask desired observations).
2. Add silver nitrate solution.
3. If the precipitate formed is white it’s silver chloride, if it’s cream then it’s silver bromide, and if it’s yellow then its siliver iodide

Question 4

How can you be certain of the result of the

halide test?

Answer 4

1. Add ammonia solution.
2. Silver chloride dissolves under dilute
   solution. Silver bromide
   dissolves under concentrated solution. Silver
   iodide will not dissolve at all.

Question 5

What is the test for ammonium ions?

Answer 5

Add sodium hydroxide solution and heat gently

if NH3 is present you can smell for it or use damp red litmus paper and hover it over the tube and it will turn blue

Question 6

Why should you not use certain acids when

performing qualitative analysis?

Answer 6

• As the acid releases the ions you're
testing into the solution so you will
OBVIOUSLY get a positive test for
follow-up tests.
• Only use these if you plan to perform
ONE TEST / NO FOLLOW-UP TESTS.
If you use HCI or H2SO4 then you will
obviously get a positive test for S04 and Cl2

Question 7

What is a precipitation reaction (with example)?

Answer 7

...When cations and anions in aqueous
solution combine to form an insoluble
ionic solid.
E.g-g
Ag* + CI - ASCI Ni?+ + 2H0 + Ni(OH)2

Question 8

in what order should you carry out anion tests?

Answer 8

Carbonate - Sulfate - Halide (Ca-S-H).
Continue if it is negative.
• Adding Ba2+ to CO3- produces a white ppt of BaCO3.
• Adding Ag2+ to CO3- produces a yellow-grey ppt of Ag2C03. • Adding Ag2+ to S042-
produces a white ppt of Ag2S04.