MODULE 3: Reactivity Trends

Question 1

How are group 2 metals and halogens related?

Answer 1

Group 2 have 2 electrons in their outer shell- two more than halogens have

Question 2

What is a reaction common with group 2 metals?

Answer 2

Redox reaction

Question 3

What is a reducing agent?

Answer 3

A substance that reduces another species

Question 4

What is an oxidising agent?

Answer 4

A substance that oxidises another species

Question 5

What products are formed when metals react with dilute acids?

Answer 5

Salt and hydrogen

Question 6

In group 2, how does reactivity change?

Answer 6

Increases

Question 7

In group 2, how does first ionisation energy change?

Answer 7

Decreases

Question 8

In group 2, why does reactivity and first ionisation energy change?

Answer 8

Due to decreased attraction between the nucleus and outer shell electrons (increased atomic radius) and increased shielding

Question 9

How does the solubility of group 2 metal hydroxides change down the group?

Answer 9

Increases down the group

Question 10

How can you measure solubility of a group 2 metal hydroxide?

Answer 10

Add spatula of anhydrous metal oxide to water, observe for solid at the bottom and test pH (pH increases down the group)

Question 11

What is calcium hydroxide used for?

Answer 11

Agriculture; increases pH of acidic soils (neutralises acid)

Question 12

What is magnesium hydroxide used for?

Answer 12

Medicine; neutralise stomach acid for indigestion (milk of magnesia)

Question 13

How do halogens exist at RTP?

Answer 13

Diatomic gas molecules (F2, Cl2)

Question 14

How does fluorine exist at RTP?

Answer 14

Pale yellow gas

Question 15

How does chlorine exist at RTP?

Answer 15

Pale green gas

Question 16

How does bromine exist at RTP?

Answer 16

Red-brown liquid

Question 17

How does iodine exist at RTP?

Answer 17

Shiny grey-black solid

Question 18

What is a displacement reaction?

Answer 18

An atom or a set of atoms is displaced by another atom in a molecule

Question 19

How can displacement reactions show reactivity in halogens?

Answer 19

A solution of the halogen is added to aqueous solutions of other halide ions (halogens with a negative charge)

Question 20

How does reactivity change in halogens?

Answer 20

Decreases moving down the group

Question 21

How can you tell that a halogen displacement has occured?

Answer 21

Added non-polar organic solvent (cyclohexane) to mix solution, if displacement has occurred colour change should take place; the solution will turn the colour of the halogen being displaced

Question 22

What are the trends in group 17 (halogens)?

Answer 22

Down the group; stronger London forces, increased boiling and melting point, decreased reactivity

Question 23

What is disproportionation?

Answer 23

A redox reaction where the same element has been both oxidised and reduced

Question 24

Name 2 examples of disproportionation reactions

Answer 24

Chlorine with water and chlorine with cold, dilute sodium hydroxide

Question 25

What are the benefits and risks of using chlorine in day-to-day life?

Answer 25

Benefits; ensure clean water, prevents devastating disease like cholera and typhoid
Risks; toxic, can bond with organic hydrocarbons from decaying vegetables to form chlorinated hydrocarbons (which may cause cancer)

Question 26

What tests can you do for anions?

Answer 26

Carbonate test, sulfate test, halide test

Question 27

What order should you carry out the tests for anions and why?

Answer 27

Carbonate, sulfate and halide; rule out possibilities of presence of other anions (think about the chemistry happening within the test)

Question 28

Describe the carbonate test

Answer 28

Carbonates react with acids to form carbon dioxide gas, so; add nitric acid to solution being tested, if you see bubbles the unknown compound could be a carbonate but to be sure it is carbon dioxide gas the gas must be bubbled through lime water (if cloudy = carbon dioxide present)

Question 29

Describe the sulfate test

Answer 29

Barium sulfate is insoluble, so; aqueous barium ions (usually as aqueous barium chloride or barium nitrate) are added to the sample being tested, if sulfate is present a white precipitate will form

Question 30

Describe the halide test

Answer 30

Silver halide is insoluble, so; add aqueous silver nitrate, if precipitate forms halide is present (white = chloride, cream = bromide, yellow = iodide), then add aqueous ammonia to test solubility of precipitate (chloride = dilute ammonia, bromide = concentrate ammonia, iodide = insoluble)

Question 31

Why is aqueous ammonia used in a halide test?

Answer 31

To easily distinguish the precipitate made as the colours are similar

Question 32

How would you continue to test for anions if there were a mixture of ions?

Answer 32

Add excess and filter off precipitate (and use barium nitrate for sulfate test so no chloride ions are added to the solution for halide test)

Question 33

What is the test for cations?

Answer 33

Ammonium ion test

Question 34

Describe the ammonium ion test

Answer 34

Aqueous sodium hydroxide is added to solution, if ammonium is present ammonia gas will be produced, mixture is warmed to release ammonia gas, test with moist pH indicator paper (blue = ammonia present)