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Chemistry GCSE > Required pracs P2 > Flashcards

Required pracs P2 Flashcards

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1
Q

How to carry out flame tests

A

Dip wire into concentrated HCl then into sample
Place in blue Bunsen flame
Record the colour of the flame

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2
Q

Why dip wire in conc HCl

A

To remove any impurities that may affect the colour of the flame

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3
Q

Precautions to take when using a Bunsen burner

A

Don’t leave unattended
Tie back long hair
Keep flammable chemicals away from the flame

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4
Q

Lithium flame test

A

Crimson flame

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5
Q

Sodium flame test

A

Yellow flame

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6
Q

Potassium flame test

A

Lilac flame

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7
Q

Calcium flame test

A

Orange-red flame

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8
Q

Copper flame test

A

Green

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9
Q

Why can a flame test not be used when a compound contains a mixture of metal ions

A

The flame colours of some ions may be masked by the colours of other metal ions

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10
Q

Test for carbonate ions

A

Add a few drops of dilute HCl to sample
Pass the gas produced through lime water
Limewater turns cloudy (precipitate of type of carbonate)

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11
Q

How to test for sulphate ions

A

Add some dilute acid (HCl)
Then add barium chloride solution
White precipitate of barium sulphate formed

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12
Q

How to test for halide ions

A 
Add some dilute nitric acid 
Then add silver nitrate
Chloride - White precipitate (solid)
Bromide - Cream precipitate (solid)
Iodide - Yellow precipitate(solid)
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13
Q

How to carry out sodium hydroxide test

A

Add a little NaOH to a solution of the compound
followed by excess NaOH
Record colour

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14
Q

Result for copper - sodium hydroxide

A

Blue precipitate of copper hydroxide, Cu(OH)2

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15
Q

Iron II - sodium hydroxide

A

Green precipitate of iron (II) hydroxide, Fe(OH)2

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16
Q

Iron III - sodium hydroxide

A

Brown precipitate of iron (III) hydroxide, Fe(OH) 3

17
Q

Calcium, magnesium, aluminium - sodium hydroxide

A

White precipitate of calcium hydroxide, Ca(OH)2

Magnesium Mg 2+ White precipitate of magnesium hydroxide, Mg(OH)2

Aluminium Al 3+ White precipitate of aluminium hydroxide, Al(OH)3

18
Q

How to tell Ca, Mg and Al apart

A

To tell them apart, we add excess sodium hydroxide:
If white precipitate dissolves: Al 3+ ions are present
If the white precipitate does not dissolve, we have either
Ca 2+ or Mg 2+ ions in a compound, so we do a flame test to
decide:
no flame colour = Mg 2+ ions
orange-red flame = Ca 2+ ions

19
Q

Sodium Thiosulphate-HCl Reaction

A

Measure 40 cm 3 of ‘thio’ into a conical flask & record solution temperature
Place it on paper that has a cross drawn on it
Measure 10 cm 3 of 0.100 moles/dm 3 HCl & record solution temperature
Add HCl to flask, start timer & swirl flask
Time disappearance of the cross
Repeat twice & calculate mean time
Repeat for different concentrations of sodium thiosulphate (dilute with water) but keep total volume constant

20
Q

Sodium Thiosulphate-HCl Reaction

variables

A

Variables
IV concentration of ‘thio’

DV time for cross to disappear

CV concentration of HCl
Volume of HCl
Total volume of ‘thio’
Constant temperature

21
Q

Improve accuracy sodium thiosulphate

A

To improve accuracy of measurements:
Use a pipette or burette to measure volumes
Use a light sensor connected to a datalogger to measure when light
intensity drops to a certain value (as precipitate forms)
Use a water bath set at a fixed temperature eg 20 0 C to keep
contents in flask at a constant temperature

22
Q

Calcium Carbonate (Marble) or Magnesium-HCl Reaction

A

Measure 20 cm 3 HCl into a conical flask & record solution temperature
Measure 1 g of Mg or CaCO 3 using a balance
Add the solid to the flask, quickly place the gas syringe bung in flask & start timer, swirling flask
Time how long it takes to collect a fixed volume of gas
Repeat twice & calculate a mean time
Repeat for different concentrations of HCl (dilute with water) but keep total volume constant
Rate = total vol of gas / time

23
Q 
Calcium Carbonate (Marble) or Magnesium-HCl Reaction
Variables
A

IV concentration of HCl

DV time for cross to disappear

CV Total volume of HCl
Same mass of solid
Constant room temperature

24
Q

Improve accuracy of Calcium Carbonate (Marble) or Magnesium-HCl Reaction

A

Use a pipette or burette to measure volumes
Use a water bath set at a fixed temperature eg 20 0 C to keep
contents in flask at a constant temperature

Chemistry GCSE (28 decks)

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