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A-Level Chemistry > 17 - Reactivity trends > Flashcards

17 - Reactivity trends Flashcards

1
Q

What is disproportionation?

A

When an element is both oxidised and reduced in a single reaction

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2
Q

What are the 2 reactions we need to know to do with disproportionation?

A

Adding chlorine to water

Making household bleach

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3
Q

Give the reaction for adding chlorine to water and explain why disproportionation happens

A

Cl~2 (aq) + H~2 O (l)
–>
HClO (aq) + HCl (aq)

The chlorine starts with an oxidation state of 0

But it ends up with -1 state in the HCl and +1 state in HClO so it has been oxidised and reduced

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4
Q

Give the reaction for making household bleach and explain why disproportionation happens

A

Cl~2 (aq) + 2NaOH (aq)
–>
NaCl (aq) + NaClO (aq) + H~2 O

Cl goes to -1 in NaCl and to +1 in NaClO

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5
Q

What is the advantage and disadvantage to adding chlorine to water?

A

Advantage is that bacteria is killed so water is drinkable

Disadvantage is the chlorine is toxic in high quantities

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6
Q

What makes a chemical a bleach?

A

It has a ClO- ion

NaClO and HClO are both bleach

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7
Q

What is the boiling point of group 17 elements like and why?

A

Low boiling points because the element only have London forces and are simple covalent

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8
Q

What happens to boiling point as you go down group 17 and why?

A

As you go down, boiling point increases

Because there are more electrons so there are more London forces

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9
Q

What happens to reactivity as you go down group 17 and why?

A

As you go down, the elements get less reactive

Because:

Radius and shielding increase

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10
Q

What is redox displacement?

A

Where you have a halide ion and a halogen which is more reactive than the halide and the negative charge goes from the halide onto the other halogen

The halogen becomes a halide ion and the halide ion becomes a halogen

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11
Q

In redox displacement

What happens when the halide is more reactive than the halogen?

A

No reaction happens because the halogen isn’t reactive enough to displace the halide

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12
Q

What is the reaction for the redox displacement of chlorine and bromide?

A

Cl~2 + 2Br-
–>
2Cl- + Br~2

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13
Q

What is redox displacement used for?

A

To find out which halide you have by making it into a halogen and looking at the colour change

Redox displacement is different to halide tests

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14
Q

What are the colours of the different halogens in both water and cyclohexane?

A

Solution in water:

Cl~2 is pale green
Br~2 is orange
I~2 is brown

Solution is cyclohexane:

Cl~2 is pale green
Br~2 is orange
I~2 is violet

Notice that only the iodine changes colour from water to cyclohexane

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15
Q

How do you do halide tests?

Different to redox displacement

A

Dissolve halide in water

Add aqueous silver nitrate

Silver halide precipitate is formed and its colour tells us what the halide is

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16
Q

In halide tests

What are the precipitate colours for the different halides?

A

Chloride gives white

Bromide gives cream

Iodide gives yellow

17
Q

How do you confirm the halide test result?

A

Add ammonia since it dissolves each halide precipitate differently

Chloride dissolves very easily

Bromide dissolves in concentrated NH~3

Iodide isn’t soluble in NH~3

18
Q

What is the ionic equation for halide tests?

A

Ag+ (aq) + X- (aq)
–>
AgX (s)

19
Q

How do you test for carbonates?

A

Add acid to produce carbon dioxide

Bubble through limewater so the carbon dioxide turns the limewater cloudy

20
Q

What do you need to know about sulfates to understand sulfate tests?

A

All sulfates are soluble in water

Except for barium sulfate

21
Q

How do you test for sulfates?

A

React compound with barium chloride or nitrate

BaSO~4 precipitate will form if compound is a sulfate

22
Q

What is the problem with sulfate tests?

What do you have to do because of this?

A

If the compound is a carbonate

The sulfate test result will be positive

This means that you have to do a carbonate test first to verify that it isn’t a carbonate

Then do the sulfate test

23
Q

If you are doing halide tests, what do you need to do in the sulfate test differently?

A

Don’t use BaCl~2 because the chlorine will make the halide test positive automatically

24
Q

How do you test for NH~4 +?

A

Add a hydroxide to produce ammonia gas

Ammonia gas is the only common alkaline gas

So use litmus paper which will turn blue if the ammonia is present

25
Q

What order do you have to do halide, carbonate, sulfate and ammonium tests?

A

Carbonate then sulfate then halide

You can do ammonium test at any point

26
Q

How do group 2 elements react with oxygen?

A

2X (s) + O~2 –> 2XO

Where X is a group 2 element

27
Q

What is formed when group 2 elements react with water?

A

A group 2 hydroxide

And hydrogen

28
Q

Give the reaction for group 2 and water

A

X (s) + 2H~2 O (l)
–>
X(OH)~2 (aq) + H~2 (g)

Where X is a group 2 element

29
Q

What is produced when metals react with acid?

A

Salt and hydrogen gas are produced

30
Q

What happens to reactivity as you go down group 2?

A

As you go down group 2, reactivity increases

31
Q

Why does reactivity increase as you go down group 2?

A

As you go down group:

Attraction decreases because

Atomic radius increases and shielding increases

32
Q

What happens when a group 2 oxide reacts with water?

A

XO + H~2 O
–>
X 2+ + 2OH -

When solution becomes saturated, precipitate is produced:

X 2+ + 2OH -
–>
X(OH)~2

33
Q

What happens to solubility of hydroxides as you go down group 2?

What does this cause?

A

Solubility of group 2 hydroxides increases as you go down group 2

So solution contains more OH ions so it is more alkaline

34
Q

What is calcium hydroxide used for practically?

A

Calcium hydroxide is used in farming to increase pH of acidic soils

35
Q

How are group 2 compounds used in medicine?

A

Group 2 compounds react with HCl in stomach to treat acid indigestion

36
Q

What is the colour of universal indicator for strong, weak acid and strong, weak alkali?

A

Strong acid is red

Weak acid is green

Strong alkali is purple

Weak alkali is blue

37
Q

What happens to litmus paper in acid and alkali?

A

What happens to litmus paper in acid and alkali?
Red in acid

Blue in alkali

38
Q

Why does increased radius and shielding make group 2 elements more reactive and group 17 elements less reactive?

A

Group 2 elements want to lose their outer electrons

Group 17 elements want to gain outer electrons

A-Level Chemistry (25 decks)

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