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
What order do you have to do halide, carbonate, sulfate and ammonium tests?
Carbonate then sulfate then halide You can do ammonium test at any point
26
How do group 2 elements react with oxygen?
2X (s) + O~2 --> 2XO Where X is a group 2 element
27
What is formed when group 2 elements react with water?
A group 2 hydroxide And hydrogen
28
Give the reaction for group 2 and water
X (s) + 2H~2 O (l) --> X(OH)~2 (aq) + H~2 (g) Where X is a group 2 element
29
What is produced when metals react with acid?
Salt and hydrogen gas are produced
30
What happens to reactivity as you go down group 2?
As you go down group 2, reactivity increases
31
Why does reactivity increase as you go down group 2?
As you go down group: Attraction decreases because Atomic radius increases and shielding increases
32
What happens when a group 2 oxide reacts with water?
XO + H~2 O --> X 2+ + 2OH - When solution becomes saturated, precipitate is produced: X 2+ + 2OH - --> X(OH)~2
33
What happens to solubility of hydroxides as you go down group 2? What does this cause?
Solubility of group 2 hydroxides increases as you go down group 2 So solution contains more OH ions so it is more alkaline
34
What is calcium hydroxide used for practically?
Calcium hydroxide is used in farming to increase pH of acidic soils
35
How are group 2 compounds used in medicine?
Group 2 compounds react with HCl in stomach to treat acid indigestion
36
What is the colour of universal indicator for strong, weak acid and strong, weak alkali?
Strong acid is red Weak acid is green Strong alkali is purple Weak alkali is blue
37
What happens to litmus paper in acid and alkali?
What happens to litmus paper in acid and alkali? Red in acid Blue in alkali
38
Why does increased radius and shielding make group 2 elements more reactive and group 17 elements less reactive?
Group 2 elements want to lose their outer electrons Group 17 elements want to gain outer electrons