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Chemical Analysis > Identufying Substances > Flashcards

Identufying Substances Flashcards

1
Q

What are metal ions also known as?

A

Cations

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2
Q

What are the two methods to test for positive ions (cations)?

A

Flame test
Sodium hydroxide

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3
Q

What is the flame test?

A
  1. Dip nichrome loop in concentrated hydrochloric acid then heat in Bunsen burger flame to clean it
  2. Dip in acid again then in the metal compound
  3. Put loop in blue flame and observe colour
    Lithium = Crimson , Sodium = Golden/yellow , potassium = lilac , calcium = brick red , copper = green
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4
Q

What colour flame does calcium produce - Ca2+?

A

Brick Red

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5
Q

What colour flame does copper produce - Cu2+?

A

Green

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6
Q

What colour flame does lithium produce - Li+?

A

Crimson/bright red

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7
Q

What colour flame does sodium produce - Na+?

A

Yellow

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8
Q

What colour flame does potassium produce - K+?

A

Lilac

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9
Q

What’s the sodium hydroxide test?

A
  1. Dissolve half a spatula of powder (you are testing) in 1cm3 of distilled water
  2. Add 2cm3 of NaOH - sodium hydroxide
  3. Swirl and observe for precipitate:
    White, Brown, green-brown,blue
    If still white add more NaOH
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10
Q

If the precipitate is white and extra sodium hydroxide dissolves the precipitate what cation will be present?

A

Al3+ -> Aluminim

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11
Q

If the precipitate is white and doesn’t dissolve with extra sodium hydroxide what cations will be present?

A

Mg2+ -> Magnesium
Ca2+ -> Calcium
This can be distinguished using a flame test - if there is no colour magnesium is present but if there is a orange red flame calcium is present

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12
Q

If the precipitate is light blue what cations will be present ?

A

Cu2+ -> copper

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13
Q

If the precipitate formed is reddish-brown what cation is present ?

A

Fe3+. -> Iron

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14
Q

If the precipitate formed is green what cation is present?

A

Fe2+. -> Iron

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15
Q

Why does iron hydroxide turn from green to brown in an open test tube (sodium hydroxide test)?

A

The iron 2+ has been oxidised to make iron 3+ which results in the brown colout

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16
Q

How do you test for halide ions?

A
  1. add a few drops of your compound
  2. Add nitric acid - removes carbonate ions
  3. Add a few drops of silver nitrate
    Chloride ions = white, Bromide ions = cream, Iodide ions = pale yellow
17
Q

When silver nitrate and nitric acid react with chloride ions what colour precipitate forms?

A

Chloride ions = white precipitate

18
Q

When silver nitrate and nitric acid react with bromide ions what colour precipitate forms?

A

Bromide ions = cream precipitate

19
Q

When silver nitrate and nitric acid react with iodide ions what colour precipitate forms?

A

Iodide ions = yellow precipitate

20
Q

How do you test for carbonate ions?

A

Add dilute acid (hydrochloric) to compound
Positive result = bubbles of carbon dioxide gas are seen or limewater turns cloudy

21
Q

What’s the positive result of a carbonate ions presence?

A

Bubbles are produced or limewater turns cloudy

22
Q

How do you test for sulfate ions?

A

Add half a spatula of powder in 1 cm3 of distilled water
Add 1cm3 of hydrochloric acid
Add 1cm3 of barium chloride and agitate

23
Q

What’s a positive result for the presence of sulphate ions?

A

A white precipitate is formed
Ba2+ + SO4 2- —> BaSO4

24
Q

What are instrumental analysis methods?

A

Gas chromatography
Mass spectroscopy
Flame emission spectroscopy

25
Q

What is instrumental analysis used in?

A

Industry (quality control)
Law enforcement forensics

26
Q

Advantages of instrumental analysis?

A

Precise, accurate, sensitive
Quick
Can test very small samples

27
Q

Disadvantages of instrumental analysis?

A

Expensive
Need special training to operate machines
Need reference data

28
Q

What does flame emission spectroscopy do?

A

Analyse metal ions in a solution

29
Q

What does spectroscopy do?

A

Measure specific wavelengths of the light emitted to identify the metal ion and it’s concentration on the lined spectrum.
Every ion emits light at a specific wavelength that is unique to that ion

Chemical Analysis (3 decks)

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