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Chemistry GCSE > Chemical Analysis > Flashcards

Chemical Analysis Flashcards

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1
Q

what do flame tests test

A

positive ions (cations) - metal ions

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2
Q

steps for flame test practical

A
  1. Dip the platinum wire into concentrated HCl
  2. Place the wire in the hottest part of the flame
  3. Repeat stages 1 & 2 until no colour is produced
  4. Dip the wire in concentrated HCl
  5. Place the wire into the chemical to be analysed
  6. Place the wire in the hottest part of the flame of bunsen burner
  7. Record colour produced
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3
Q

Why do we use a platinum wire

A

unreactive, doesn’t colour flame, high mpt

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4
Q

what type of flame do we use for the bunsen burner

A

a blue non-cone flame

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5
Q

Flame Test - Lithium

A

crimson red

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6
Q

Flame Test - Sodium

A

yellow/orange

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7
Q

Flame Test - Potassium

A

lilac

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8
Q

Flame Test - Calcium

A

brick red

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9
Q

Flame Test - Copper

A

green-blue

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10
Q

Flame Test - Barium

don’t have to know

A

apple green

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11
Q

Flame Test - Strontium

don’t have to know

A

red

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12
Q

what is the NaOH test used for

A

A coloured precipitate is produced when NaOH solution is added to a solution containing other positive ions

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13
Q

Steps for NaOH test

A
  1. Add no more than 1cm³ of chosen ion solution to test tube
  2. Record colour of solution
  3. Add no more than a few drops of NaOH solution to this test tube
  4. Record observations
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14
Q

how does the test differ for Ammonium

A

you will need to heat the resulting solution gently and insert a piece of damp red litmus paper

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15
Q

how does the test differ for Al and Ca

A

add excess NaOH to resulting solution to distinguish between them

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16
Q

NaOH test - Copper (II)

A

blue solution -> blue ppt

17
Q

NaOH test - Iron (II)

A

clear solution -> green ppt

18
Q

NaOH test - Iron (III)

A

orange solution -> orange/brown ppt

19
Q

NaOH test - Ammonium

A

NH3 gas produced - turns damp red litmus blue

20
Q

NaOH test - Aluminium

A

clear solution -> white ppt -> clear solution

turns back to clear solution when you add excess NaOH

21
Q

NaOH test - Calcium

A

clear solution -> white ppt

doesn’t turn back to clear solution even after excess NaOH is added

22
Q

Sulphate test steps

A
  1. Add a few drops of HCl acid to solution of BaCl2
  2. Add a few drops of acidified BaCl2 to unknown substance
  3. Record observations

after step 1, BaCl2 is now acidified BaCl2

23
Q

what is the positive result for the Sulphate test

A

a white ppt is formed (BaSO4)

24
Q

Why is HCl added to BaCl2 solution

A

to prevent formation of other unwanted (white) ppts that give a false positive

e.g. BaCO3

25
Q

Halide ion test steps

A
  1. Add a few drops of HNO3 to AgNO3 solution
  2. Add no more than 1cm³ of the halide to a test tube
  3. Carefully add a few drops of the acidified AgNO3 solution to your halide
  4. Record observations

after step 1, AgNO3 is now acidified AgNO3

26
Q

Halide ion test - Chloride

A

white precipitate

AgCl

27
Q

Halide ion test - Bromide

A

cream precipitate

AgBr

28
Q

Halide ion test - Iodide

A

yellow precipitate

AgI

29
Q

why is nitric acid added to AgNO3 solution

A

to prevent any unwanted ppts that may form

e.g. Ag2CO3

30
Q

Carbonates test steps

A
  1. Place 1cm³ of your “carbonate” (or 1 spatula if solid) into test tube
  2. Add a delivery tube to it to another test tube
  3. To the second test tube, fill it up with limewater up to where the delivery tube reaches
  4. Add some acid to first test tube e.g. HCl
  5. Place bung on top of first test tube
  6. Record results
31
Q

positive result of Carbonate test

A

effervescence

if passed through limewater, it turns cloudy

32
Q

what is limewater

A

Ca(OH)2 (aq)

33
Q

reaction of carbonate and acid

A

produces salt, water, carbon dioxide

34
Q

what makes the limewater go cloudy

A

CaCO3 - precipitate

formed from reaction of limewater and CO2

35
Q

what would you see if CO2 was bubbled through limewater for a longer period of time

A

turns colourless again

36
Q

why does limewater turn colourless again if CO2 was bubbled through it for a longer period of time

A

CaCO3 + H2O + CO2 -> Ca(HCO3)2 (aq)

Ca(HCO3)2 is soluble so solution becomes colourless again

37
Q

why may effervescing stop after a few seconds when acid is added to carbonate

A

reaction forms precipitate which coats any remaining carbonate therefore preventing further reaction with acid meaning no more CO2 is produced so no more effervescence.

Chemistry GCSE (4 decks)

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