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chem > chem chap 9 - qualitative analysis > Flashcards

chem chap 9 - qualitative analysis Flashcards

1
Q

what are the reagents used to identify cations?

A

NaOH aq - sodium hydroxide
NH3 aq - ammonia

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2
Q

which cations do not give precipitates with reagents

A

group 1 cations

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3
Q

what are the 3 things to note when identifying cations

A

colour of any precipitate formed (if any) when reagent is added

whether precipitate is soluble or insoluble in an excess of the reagent

whether ammonia gas is given off in addition to naoh

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4
Q

what are the steps to test for cations?

A

pour 2cm3 of the solution into a test tube

add 3-5 drops of reagent and record observation

no ppt - warm mixture, record colour change of litmus paper

ppt - add reagent in excess
dissolves -> soluble in excess
not dissolve -> insoluble in excess

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5
Q

what is the result of adding reagents to al2+ cation?

A

naoh
white precipitate of al(oh)2 forms
precipitate forms in access to form colourless solution

nh3
white precipitate of al(oh)2 forms
precipitate dissolves in excess

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6
Q

what is the result of adding reagents to zn2+ cation

A

both naoh and nh3
white precipitate od zn(oh)2
precipitate dissolves in excess to form colourless solution

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7
Q

what is the result of adding reagents to ca2+ cation?

A

naoh
white precipitate of ca(oh)2 forms
precipitate is insoluble in excess

nh3
no precipitate is formed
no change is observed

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8
Q

what is the result of adding reagents to cu2+ cation?

A

naoh
light blue precipitate of cu(oh)2 is formed
precipitate is insoluble in excess

nh3
light blue precipitate of cu(oh)2
precipitate dissolves in excess to form dark blue solution

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9
Q

what is the result of adding reagents to fe2+ cation?

A

naoh & nh3
green precipitate of fe(oh)2 forms
precipitate is insoluble in excess
precipitate turns brown on standing

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10
Q

what is the result of adding reagents to fe3+ cation?

A

naoh & nh3
red-brown precipitate of fe(oh)3 forms
precipitate is insoluble in excess
precipitate turns brown on standing

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11
Q

what is the result of adding naoh to nh4+ cation?

A

no precipitate formed
on heatint nh3 gas is given off
nh3 gas turns damp red litmus paper blue

no change is observed when naoh is added in excess

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12
Q

what are precipitates?

A

the formation of insoluble solids from 2 solutions

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13
Q

what is the precipitate formed in the reactions of a cation with reagents

A

hydroxide of a metal ion

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14
Q

what is test for co3²‐ and the observation

A

add dilute acid
bubble the gas given off into limewater

efferversence is observed
gas gives off white precipitate of caco3 with limewater
carbon dioxide gas is produced

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15
Q

what is test for cl‐ and the observation

A

add hno3 aq
add agno3 aq

white precipitate of agcl2 is formed

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16
Q

what is test for so4²‐ and the observation

A

add hno3 aq
add ba(no)3 aq

white precipitate of baso4 is formed

17
Q

what is test for no3‐ and the observation

A

add naoh aq
add a piece of aluminium
warm mixture
test gas given off with a piece of damp red litmus paper

efferversence is observed
gas gicen off turns damp red litmus paper blue

nh3 gas produced

18
Q

what is test for h2 and the observation

A

place a burning splint at the mouth of the test tube

burning splint is extinguised with a “pop” sound

19
Q

what is test for o2 and the observation

A

insert a glowing splint into the test tube
glowing splint is rekindled

20
Q

what is test for co2 and the observation

A

bubble the gas through limewater
a white precipitate of caco3 is formed and dissolves upon further bubbling

21
Q

what are the 3 odourless/colourless gases

A

h2
o2
co2

22
Q

what are the 3 pungent gases

A

cl2
so2
nh3

23
Q

what is the colour and odour of cl2

A

yellow-green gas
pungent smell

24
Q

what is the colour and odour of so2

A

colourless gas
pungent smell

25
Q

what is the colour and odour of nh3

A

colourless gas
pungent smell

26
Q

what is test for cl2 and the observation

A

place a piece of damp blue litmus paper at the mouth if the test tube

damp blue litmus paper turns red and then bleached

27
Q

what is the colour and odour of so2

A

place a piece or filter paper soaked with acidified potassium manganate(vii) at the mouth of the test tube

purple potassium manganate(vii) turns colourless

28
Q

what is the colour and odour of nh3

A

place a piece of damp red litmus paper at the mouth of the test tube

damp red litmus paper turns blue

chem (11 decks)

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