chemical analysis 4.6

Question 1

what is the test for hydrogen?

Answer 1

squeaky pop test:
complete a sample of gas in test tube
attempt to ignite the gas using a lit splint

squeaky pop sound
2H2(g) + O2(g) > 2H2O(g)

Question 2

what’s the test for oxygen?

Answer 2

glowing splint test:
collect oxygen in test tube
place a glowing splint into the tube

splint relights
relights because pure O2 is more concentrated than O2 in normal air

Question 3

what’s the test for water?

Answer 3

copper sulfate test:
add anhydrous copper sulfate (CuSO4)

colour change from white to blue (hydrated)

Question 4

what’s the test for purity of water?

Answer 4

measuring BP:
meaning boiling point

closer to 100 degrees = more pure

Question 5

what’s the test for carbon dioxide?

Answer 5

limewater test:
bubble a sample of gas through limewater

a white precipitate forms (turns cloudy)
limewater - saturated calcium hydroxide forms calcium carbonate

Question 6

what’s the test for chlorine?

Answer 6

damp blue litmus paper test:
place damp blue litmus paper in a sample of gas

turns white (bleaches)
Cl2 is a good bleaching agent, removes colour

Question 7

what’s the test for ammonia?

Answer 7

damp red litmus test:
place damp red litmus paper in a sample of gas

turns blue
alkaline

Question 8

what are cations and name some?

Answer 8

positive ions
Li+, Na+, K+, Ca2+, Cu2+, Fe2+, Fe3+, NH4+

Question 9

how do you conduct a flame test?

Answer 9

• dip a piece of nichrome/ platinum wire into hydrochloric acid, cleaning the wire
• dip wire into sample of solid or solution
• place tip of wire into non-luminous bunsen flame

Question 10

if flame colour is red what type of metal cation is it?

Answer 10

Li+ lithium

Question 11

if flame colour is yellow what type of metal cation is it?

Answer 11

Na+ sodium

Question 12

if flame colour is lilac what type of metal cation is it?

Answer 12

K+ potassium

Question 13

if flame colour is orange-red what type of metal cation is it?

Answer 13

Ca2+ calcium

Question 14

if flame colour is blue-green what type of metal cation is it?

Answer 14

Cu2+ copper

Question 15

how do you conduct a sodium hydroxide test? (NaOH)

Answer 15

• dissolve the sample in water
• add a few drops of NaOH(aq)

Question 16

if the precipitate colour is blue in a NaOH test what is the metal cation?

Answer 16

Cu2+ copper
Cu(OH)2

Question 17

if the precipitate colour is green in a NaOH test what is the metal cation?

Answer 17

Fe2+ iron
Fe(OH)2

Question 18

if the precipitate colour is brown in a NaOH test what is the metal cation?

Answer 18

Fe3+ iron
Fe(OH)3

Question 19

how do you conduct the ammonium test?

Answer 19

• dissolve the sample in water
• add some NaOH(aq) and warm it
• test the gas evolved with damp red litmus paper

if NH4+ is present the litmus paper will turn blue

Question 20

what are anions and name some examples?

Answer 20

negative ions
Cl-, Br-, I-, CO3 2-, SO4 2-

Question 21

how to conduct the test for halides/ silver nitrate test?

Answer 21

• dissolve sample in water
• add nitric acids (HNO3)
• add silver nitrate (AgNO3) solution

Question 22

if a white precipitate forms when testing for halides/ silver nitrate test what type of halide ion?

Answer 22

Cl- chlorine
AgCl

Question 23

if a cream precipitate forms when testing for halides/ silver nitrate test what type of halide ion?

Answer 23

Br- bromide
AgBr

Question 24

if a yellow precipitate forms when testing for halides/ silver nitrate test what type of halide ion?

Answer 24

I- iodine
AgI

Question 25

what is important to do when testing for halides/ silver nitrate test?

Answer 25

add nitric acid as silver ions form precipitates so nitric acid so stops false positives

Question 26

how do you test for carbonate ions?

Answer 26

• add hydrochloric acid HCl and look for effervescence
• if there is effervescent bundle the gas through limewater

if carbonate ions were present the gas evolved would turn limewater cloudy

Question 27

what is important to check/ do with the carbonate test?

Answer 27

check gas evolved is CO2 using limewater as acids also evolve a gas so preventing false positives

Question 28

how do you conduct the test for sulfate ions?

Answer 28

• add hydrochloric acid look for effervescence
• if no effervescence add barium chloride solution

if sulfate is present they will form a white precipitate

Question 29

what is important to do in a sulfate test?

Answer 29

adding HCl as carbonate ions can also form a white precipitate preventing a false positive