ion tests

Question 1

test for carbonates

Answer 1

1. add dilute NITRIC ACID to solution
2. will form bubbles (but could be hydrogen bubbles so test for CO2 bubbles)
3. bubble through limewater
4. if turns cloudy- solution contains carbonate

Question 2

test for sulfates

Answer 2

1. add barium nitrate to solution
2. if sulfate present, Ba ions and SO4 ions react and form barium sulfate which is insoluble
3. if white precipitate forms, solution contains sulfate

Question 3

what is a precipitation reaction

Answer 3

two aqueous solutions react to form a solid

Question 4

test for halides

Answer 4

1. add dilute NITRIC ACID
2. add silver nitrate solution- reacts with halide and forms silver halide
3. silver halide is solid- precipitate

Question 5

ionic equation for halide test

Answer 5

Ag+(Aq) + X-(Aq) -> AgX (s)

Question 6

precipitate colours for Cl, Br, I in halide test

Answer 6

Cl- white
Br- cream
I- yellow

Question 7

how to distinguish between precipitates of Cl, Br, I

Answer 7

Cl- dissolves in dilute NH3
Br- dissolves in concentrated NH3
I- does not dissolve in either

Question 8

test for ammonium

Answer 8

1. add sodium hydroxide solution
2. warm the mixture with water bath and ammonia gas is released
3. DAMP,RED litmus will turn BLUE as the ammonia is alkaline

Question 9

ionic equation for ammonium test

Answer 9

NH4+ + OH- -> NH3(g) + H20(l)

Question 10

why do you use HNO3 in carbonate test instead of HCL or H2SO4?

Answer 10

because HCL would show up in halide test
and SO4 would show up in sulfate test

Question 11

what order are the tests completed in

Answer 11

1. carbonate
2. sulfate
3. halide

Question 12

why is carbonate test first

Answer 12

because neither sulfate or halide produce bubbles with acid
if bubbles form you know it is not sulfate or halide

if there are no bubbles, it is not a carbonate

Question 13

why is sulfate test second

Answer 13

barium carbonate (BaCO3) is white and insoluble, so if you did the sulfate test first before carbonate test, you would still get a white precipitate, even though it is a carbonate not sulfate

so do carbonate test first and look for bubbles

Question 14

why is halide test third

Answer 14

silver carbonate (Ag2CO3) and silver sulfate Ag2SO4 both form precipitates in halide test, even though they are not halides.

so carry out carbonate and sulfate test first

Question 15

why is barium used in sulfate test?

Answer 15

barium sulfates are insoluble, form a solid precipitate

Question 16

why is silver used in halide test?

Answer 16

silver halides are insoluble, form a solid precipitate

Question 17

how to do all tests on 1 solution?

Answer 17

1. carbonate test- keep adding dilute HNO3 until no more bubbles, no more CO3 left (use HNO3 not H2SO4 as the SO4 ions would show in sulfate test)
2. add BaNO3 to the same solution leftover, forms white precipitate- filter out precipitate, no more SO4 left
   (use BaNO3 not BaCl as the Cl ions would show in halide test)
3. add AgNO3 to leftover solution, forms halide precipitate, dissolve in ammonia to identify which halide

Question 18

why might you not see bubbles forming when ammonia gas forms?

Answer 18

ammonia is very soluble in water