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GCSE Chemistry > Topic 10 - Ion Tests And Nanomaterials > Flashcards

Topic 10 - Ion Tests And Nanomaterials Flashcards

1
Q

Some metal ions can be identified using what ?

A

using flame tests

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2
Q

When Calcium (Ca2+) ion burns what colour does it go ?

A

Orange-red flame

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3
Q

What Sodium (Na+) ion burns what colour flame is produced ?

A

Yellow flame

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4
Q

When Potassium (K+) ion is burnt what colour flame is produced ?

A

Lilac flame.

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5
Q

When Copper (Cu2+) ion is burnt what colour flame is produced ?

A

Blue-green flame.

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6
Q

When Lithium (Li+) ion is burnt what colour flame does it produce ?

A

Crimson flame.

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7
Q

Why is it problematic for interpreting the results of a flame test if a sample is made up of multiple ions?

A

If the sample consists of a mixture of metal ions, the flame colours of some may be masked, which can lead to incorrect interpretations.

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8
Q

We can use flame tests to identify the what ?

A

the metal ions in an ionic compound.

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9
Q

What are the steps of the flame test ?

A

Submerge a nichrome wire loop in dilute hydrochloric acid to make sure that it is clean.

Place the nichrome wire loop into the sample to be tested.

Hold the nichrome wire loop in a Bunsen burner’s blue flame.

Observe any change in colour of the Bunsen flame.

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10
Q

In flame tests, what must the nichrome wire loop be submerged in to be cleaned?

A

Dilute hydrocloric acid

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11
Q

Where can metal ions be found ?

A

aqueous solutions of metal compounds

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12
Q

Metal ions can be found in aqueous solutions of metal compounds.
How can these ions precipitate out of solution ?

A

when they react with a sodium hydroxide solution (NaOH).

This produces insoluble solids (don’t dissolve in water) called precipitates.

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13
Q

When reacted with a sodium hydroxide solution (NaOH).

What happens to calcium ions ?

A

Calcium ions (Ca2+) form the white precipitate calcium hydroxide.

Ca2+(aq) + 2OH-(aq) → Ca(OH)2(s).

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14
Q

When reacted with a sodium hydroxide solution (NaOH).

What happens to magnesium ions ?

A

Magnesium ions (Mg2+) form the white precipitate magnesium hydroxide.

Mg2+(aq) + 2OH-(aq) → Mg(OH)2(s).

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15
Q

When reacted with a sodium hydroxide solution (NaOH).

What happens to amluminum ions ?

A

Aluminium ions (Al3+) form the white precipitate aluminium hydroxide.

Al3+(aq) + 3OH-(aq) → Al(OH)3(s)

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16
Q

Unlike the other two white precipitates, aluminium hydroxide can be dissolved in excess NaOH.
What does this produce ?

A

This produces a colourless solution

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17
Q

When reacted with a sodium hydroxide solution (NaOH).

What happens to iron(II) ions ?

A

Iron(II) ions (Fe2+) form the green precipitate iron(II) hydroxide.

Fe2+(aq) + 2OH-(aq) → Fe(OH)2(s).

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18
Q

When reacted with a sodium hydroxide solution (NaOH).

What happens to ammonium ions ?

A

Ammonium (NH4+) ions form water and ammonia. Ammonia gas evolves out of the solutions.

NH4+(aq) + OH-(aq) → NH3(g) + H2O(l),

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19
Q

When reacted with a sodium hydroxide solution (NaOH).

What happens to copper ions ?

A

Copper ions (Cu2+) form the blue precipitate copper(II) hydroxide.

Cu2+(aq) + 2OH-(aq) → Cu(OH)2(s).

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20
Q

When reacted with a sodium hydroxide solution (NaOH).

What happens to iron(III) ions ?

A

Iron(III) ions (Fe3+) form the brown precipitate iron(III) hydroxide.

Fe3+(aq) + 3OH-(aq) → Fe(OH)3(s).

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21
Q

How do we test for ammonia gas ?

A

Ammonia gas can be identified by placing damp red litmus paper at the mouth of the test tube.
The litmus will turn blue if ammonia gas is present.

22
Q

What are characteristics of all carbonates ?

A

CO3^2- ions are characteristic of all carbonates.

23
Q

A reaction between a carbonate and a dilute acid gives what ?

A

a salt, carbon dioxide and water.

24
Q

Whats an example of a reaction between a carbonate and dilute acid ?

A

Calcium carbonate + hydrochloric acid → calcium chloride + carbon dioxide + water

25
Q

How do we test for carbon dioxode ?

A

bubbling the gas through limewater. If the solution turns cloudy, the gas is carbon dioxide.

26
Q

How do we test for carbonates ?

A

CO3^2- ions are characteristic of all carbonates.
A reaction between a carbonate and a dilute acid gives a salt, carbon dioxide and water.

E.g. Calcium carbonate + hydrochloric acid → calcium chloride + carbon dioxide + water

As carbon dioxide is produced, we can use the standard carbon dioxide test to work out if an unknown substance is a carbonate.

This test involves bubbling the gas through limewater. If the solution turns cloudy, the gas is carbon dioxide.

27
Q

What do all compunds of sulfate contain ?

A

contain SO4^2- ions

28
Q

How do we test for sulfate ions ?

A

Add dilute hydrochloric acid to an unknown solution - this removes carbonate ions.

These could disrupt test results by forming a precipitate with the barium ions added in step 2.

Add barium chloride to the same solution - If sulfates are present, the white precipitate barium sulfate will form:

Ba^2+(aq) + SO4^2-(aq) → BaSO4(s)

29
Q

What charge do anions carry ?

A

Net Negative charge

30
Q

How many steps are there in sulfate testing ?

A

2

31
Q

Simplified - what are the two steps in sulfate testing ?

A

1 - Add dilute hydrochloric acid

2- add braium chloride

32
Q

How could you confirm that carbonates produce carbon dioxide when they react with dilute acids?

A

Bubble the gas produced through limewater.

If the solution turns cloudy, we can say that carbon dioxide has been produced and, therefore, the unknown substance is a carbonate.

33
Q

What charge are halide ions ?

A

Negatively charged

Anions

34
Q

How do we test for halide ions ?

A

1 - Add dilute nitric acid to an unknown solution.

  • This removes carbonate ions.
  • These could disrupt test results by forming a precipitate with the silver ions added in step 2.

2 -Add silver nitrate to the same solution.
- If halide ions are present, they will form a precipitate with the silver ions:

Ag+(aq) + Cl-(aq) → AgCl(s) (silver chloride is white)
Ag+(aq) + Br-(aq) → AgBr(s) (silver bromide is cream)
Ag+(aq) + I-(aq) → AgI(s) (silver iodide is pale yellow)

35
Q

In the reaction between silver ions and chlorine ions what colour is the precipitate ?

A

Ag+(aq) + Cl-(aq) → AgCl(s) (silver chloride is white)

36
Q

In the reaction between silver ions and bromine ions what colour is the precipitate ?

A

Ag+(aq) + Br-(aq) → AgBr(s) (silver bromide is cream)

37
Q

In the reactions between silver ions and iodine ions what colour is the precipitate ?

A

Ag+(aq) + I-(aq) → AgI(s) (silver iodide is pale yellow)

38
Q

What is the order of the test for cations ?

A

Flame test.

Coloured precipitates with sodium hydroxide.

Testing the gas evolved for ammonium.

39
Q

Whats the order of tests for anions ?

A

Test for carbonate - test for carbon dioxide gas to confirm a positive result.

Test for sulfates - the presence of a white barium sulfate precipitate confirms a positive result.

Test for halide ions - the colour of silver halide corresponds to halide anion in a positive result.

40
Q

What is the order for testing for anions, and why must testing for anions be done in a certain order?

A

Test for carbonate.
Test for sulfates.
Test for halide ions.
If any HCl or BaCl2 is added to test for carbonate or sulfate, there will be chloride ions in the solution.
These will be tested and there will be a false positive result for chloride ions.

41
Q

What are the advantages of using instrumental methods ?

A

Greater sensitivity and accuracy.
Quicker at producing results.
Able to analyse tiny samples.

42
Q

What are the disadvantages of using instrumental methods ?

A

The instruments are often expensive.
You need to go through special training to operate the instruments.
The results are often only useful when compared to data from known substances.

43
Q

Why are Instrumental methods better than traditional methods ?

A

More accurate
More sensitive
Quicker at producing results
Can analyse small samples

44
Q

What is Flame emission spectroscopy ?

A

an instrumental method used to work out the identity and concentration of the metal ions present in a solution

45
Q

What are the steps of Flame emission spectroscopy ?

A

Step 1
Place a sample of the metal solution being tested into a flame. Light will be given off.

Step 2
The light that is given off is captured by a spectroscope.
This instrument generates a line spectrum by distinguishing between light with different wavelengths.

46
Q

We analyse the line spectra produced by flame emission spectroscopy to see what ?

A

which metal ions are present and their concentrations.

47
Q

Each metal ion will generate a distinct line spectrum what does this mean ?

A

This means that we can identify all ions present in a solution.

48
Q

The concentration of an ion is indicated by what ?

A

the intensity of line spectra

49
Q

Unlike flame tests what does flame emission spectroscopy allows us to analyse ?

A

mixtures by comparing them with reference spectra.

50
Q

How we can find out the absorption pattern ?

A

If we place a known concentration of a sample in a machine

We can do this with many samples and create a graph of concentration and absorption.

If an unknown sample is placed in the machine, we can find out its absorption and then use the graph to find out the concentration.

51
Q

What feature of a line spectrum provides information about the concentration of a metal ion?

A

Intensity

52
Q

Why are Instrumental methods worse than traditional methods ?

A

Expensive
Specialised training required
Results are only useful in context of data from known substances

GCSE Chemistry (10 decks)

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