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A-Level Chemistry OCR B > Practical Skills > Flashcards

Practical Skills Flashcards

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1
Q

What substance would be used to test for NH4+ ions, group 2 ions and transition metals (i.e. cations)?

A

Excess NaOH

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2
Q

Describe the tests for Mg2+ and Ca2+ ions

A

Add excess NaOH, a white precipitate will form of Mg(OH)2 or Ca(OH)2

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3
Q

Explain why NaOH cannot be used to test for all group 2 metals

A

Solubility of metal hydroxides increases down the group, so a precipitate of metal hydroxide will not form for strontium and barium

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4
Q

Describe the precipitate results for:

copper solutions
iron (II)
iron (III)
manganese (II)
chromium (III)
A 
copper - blue ppt
iron (II) - green ppt
iron (III) - brown ppt
manganese (II) - pale brown ppt
chromium (III) - green ppt
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5
Q

Explain the test for ammonium ions (NH4+)

A

a) Place ammonium chloride in a test tube.
b) Add sodium hydroxide solution. Shake
c) Warm gently using a water bath.
d) Test the fumes by holding a piece of damp red litmus
paper in the mouth of the test tube (alkali ammonia gas), if present will turn blue

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6
Q

Describe how you would test for strontium and barium ions (Sr2+, Ba2+)

A

Add excess sulfuric acid, strontium and barium will form white precipitates with addition of sulfate ions.

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7
Q

Explain why sulfuric acid would not be used to test for Ca2+ and Mg2+

A

Group 2 sulfates become less soluble down the group, so calcium and magnesium sulfates would not form a precipitate

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8
Q

Describe the test for sulfate ions

A

Add acidified BaCl2 (with HCl)

White precipitate of BaSO4 will form if present

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9
Q

Explain why HCl is used when testing for sulfate ions. Can H2SO4 be used instead?

A

HCl used to react with any carbonates impurities that would form a white barium carbonate precipitate and so give a false result.
You could not use sulfuric acid because it contains sulfate ions and so would give a false positive result

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10
Q

Describe the test and results for halide ions

A

Acidify solution w HNO3 (to react with carbonate impurities), then add silver nitrate dropwise.
Fluorides produce no precipitate
Chlorides produce a white precipitate
Bromides produce a cream precipitate
Iodides produce a pale yellow precipitate

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11
Q

How can the results for halide ion tests be made more clear?

A

Add ammonia solution to help differentiate if they look similar

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12
Q

Describe the test for carbonate ions

A

Add any dilute acid and observe effervescence.

Bubble gas through limewater to test for CO2 – will turn limewater cloudy

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13
Q

Describe the test for hydroxide ions

A

Alkaline hydroxide ions will turn red litmus paper blue.

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14
Q

Describe the test for alkenes

A

To 0.5 cm3 of bromine water in a test tube add a few drops of the unknown and shake. Observation: alkenes should decolourise bromine water

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15
Q

Briefly describe the method for partial oxidation of a primary alcohol

A

Reaction: primary alcohol –> aldehyde
Reagent: potassium dichromate (VI) solution and dilute sulfuric acid.
Conditions: (use a limited amount of dichromate) warm gently and distil out the aldehyde as it forms

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16
Q

Describe safety measures when partially oxidizing a primary alcohol

A

Wear gloves when handling solid potassium dichromate(Vl) since it is highly toxic and a category 2 carcinogen; it is also an irritant. Avoid inhaling any dust. Concentrated sulfuric acid is corrosive.

17
Q

Briefly describe the method for complete oxidation of a primary alcohol

A

Reaction: primary alcohol –> carboxylic acid
Reagent: potassium/sodium dichromate(VI) solution and
sulfuric acid
Conditions: use an excess of dichromate, and heat under reflux: (distil off product after the reaction has finished)

18
Q

What observation would you see when oxidizing an alcohol

A

Observation: the orange dichromate ion (Cr2O72-) reduces to the green Cr 3+ ion

19
Q

Describe the test for a carboxylic acid

A

The presence of a carboxylic acid can be tested by addition of sodium carbonate. It will fizz and produce carbon dioxide

20
Q

Can phenol react with metal carbonates and metal hydroxides?

A

Both phenols and carboxylic acids will react with sodium metal and sodium hydroxide. Only carboxylic acids will react with sodium carbonate as a phenol is not strong enough an acid to react.

21
Q

Describe the test for phenols

A

Phenol reacts in iron (III) chloride solution to form a purple complex

22
Q

Describe test for nitrate (V) ions

A

Warm with Devarda’s alloy and NaOH, ammonia is produced, turning damp red litmus paper blue

23
Q

Describe the test for lead ions (Pb2+)

A

Add solution of potassium iodide, a bright yellow precipitate of lead iodide will form

A-Level Chemistry OCR B (8 decks)

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