CHAPTER 8 - REACTIVITY TRENDS

Question 1

Why are group 2 elements known as reducing agents

Answer 1

They reduce other species

They are oxidised

eg. Ca —> Ca2+ + 2e-

Question 2

What is formed when a redox reaction occurs between a metal and oxygen

Answer 2

Metal Hydroxide

eg. 2Mg + O2 –> 2MgO

Question 3

What is formed when a redox reaction occurs between a metal and water

Answer 3

Metal Hydroxide + Hydrogen

eg. Sr + 2H2O –> Sr(OH)2 + H2

Question 4

What is formed when a redox reaction occurs between a dilute acid and metal

Answer 4

Salt and Hydrogen

eg. Mg + 2HCl –> MgCl2 + H2

Question 5

What are the solubility of Barium, Calcium, Magnesium and Strontium Hydroxides

Answer 5

Ba(OH)2 - Most soluble
Sr(OH)2
Ca(OH)2
Mg(OH)2 - Least soluble

Question 6

Describe an experiment to show the trends in solubility of metal hydroxides

Answer 6

Add a spatula of each group 2 oxide to water in a test tube

Shake the mixture. On this scale, there is insufficient water to dissolve all of the metal hydroxide that forms. You will have a saturated solution of each metal hydroxide with some white solid undissolved at the bottom of the test-tube

Measure pH of each solution. The alkalinity will be sen to increase down the group

Question 7

What are group 2 compounds used for in agriculture

Answer 7

Calcium Hydroxide added to fields as lime by farmers to increase pH of soils

Ca(OH)2 + 2H+ –> Ca2+ + 2H2O

Question 8

What are group 2 compounds used for in medicine

Answer 8

Antacids to treat indigestion eg. Milk of magnesia or Calcium carbonates to neutralise stomach acids

Question 9

Explain why group 2 elements are reducing agents

Answer 9

Group 2 metals add electrons to other species

Question 10

Explain why the group 2 elements become more reactive down the group

Answer 10

Down group 2, the total energy from 1st and 2nd ionisation energies decreases because of increased atomic radius and increased shielding

It therefore becomes easier to remove the electrons and the reactivity increases

Question 11

State and explain the trend in alkalinity of the solution formed when group 2 oxides are added to water

Answer 11

Group 2 oxides react with water forming the metal hydroxide.

Hydroxide ions in solution cause alkalinity.

Down group 2, the solubility of the metal hydroxide increases, increasing the pH and alkalinity

Question 12

What is the name of Group 17 (7)

Answer 12

The halogens

Question 13

Where to halogens occur

Answer 13

Stable halide ions, dissolved in sea water or combined with sodium or potassium deposits in salt mines

Question 14

What colours and states do halogens form at RTP

Answer 14

Fluorine - Yellow Gas
Chlorine - Green Gas
Bromine - Red-Brown liquid
Iodine - Grey-black solid

Question 15

Why are halogens known as oxidising agents

Answer 15

They cause oxidation in other species

causing themselves to be reduced

Question 16

What is the trend of reactivity down the halogen group

Answer 16

It Decreases

Question 17

What colours do Chlorine, bromine and iodine form in water

Answer 17

Cl - Pale green
Br - Orange
I - Brown

Question 18

What colours do Chlorine, Bromine and Iodine form in cyclohexane

Answer 18

Cl - Pale green
Br - Orange
I - Violet

Question 19

Why do halogens dissolve more readily into cyclohexane than water

Answer 19

Halogens and cyclohexanes are non-polar

Water is polar

Question 20

What is the Displacement trend in halogens

Answer 20

Cl displaces Br and I
Br displaces I
I displaces nothing
(pg 113)

Question 21

What is the displacement reaction of chlorine and sodium bromide

Answer 21

Cl2 + 2NaBr –> 2NaCl + Br2

Question 22

What is a disproportionation reaction

Answer 22

A redox reaction in which the same element is both oxidised and reduced

Question 23

What is chlorine used for

Answer 23

Water purification killing harmful bacteria

Cl2 + H2O –> HClO + HCl

Question 24

How can a disproportionate reaction be seen

Answer 24

Adding indicator into a solution of chlorine and water

Turns red in the presence of HCl and disappears after the bleaching action of HClO (Chloric acid)

Question 25

What is formed in the reaction of Cold, dilute NaOH (aq)

Answer 25

NaClO, NaCl and H2O Disproportionation reaction

Question 26

What is the test for Halide ions

Answer 26

Adding Aqueous silver ions, eg. Silver nitrate

Question 27

State and explain the trend in boiling points of the halogens fluorine to iodine

Answer 27

Boiling point increases due to increasing electrons downgrade This increases the strength of the London forces are more energy needed to break the intermolecular forces

Question 28

What is the test for carbonate ions

Answer 28

Add Dilute nitric acid - effervescences OR Lime water test (Ca(OH)2) - goes cloudy

Question 29

What is the test for Sulfate ions

Answer 29

Add Barium Chloride or barium nitrate Will form BaSO4 - white ppt SBC

Question 30

What is the test for Halides

Answer 30

Add aqueous AgNO3 - forms 3 ppts of different colours, AgX Add Aqueous NH3 - to test solubility Cl - White ppt, Soluble Dilute NH3 Br - Cream ppt, soluble conc. NH3 I - Yellow ppt, Insoluble conc. NH3 HAgA

Question 31

What is the correct order for Anion testing and why

Answer 31

1- Carbonate - no other test produces bubbles after this 2- Sulfate - forms white ppt, important to make sure it isn't a carbonate which would look like a positive test if done after this due to the colour 3- Halide test, silver carbonate and silver sulfate will form precipitates insoluble in water

Question 32

What is the test for ammonium

Answer 32

Add aqueous NaOH Ammonia Gas will be produced - little bubbles formed as it is soluble with water Mixture is warmed by reaction Smell of ammonia and alkaline ammonia gas will turn damp pH paper blue

Question 33

How could you distinguish between NaCl, NaBr and NaI by a simple test?

Answer 33

Add AgNO3 to aqueous solutions of each. NaCl forms white ppt, dissolves In dilute NH3 NaBr forms cream ppt which dissolves in concentrated NH3 NaI forms yellow ppt, insoluble in conc NH3

Question 34

Explain why it is important to carry out the carbonate test before carrying out the sulfate test on an unknown chemical

Answer 34

Dilute Nitric acid with carbonate ions, and no precipitate of barium carbonate will then form

Question 35

Explain why if you are testing a mixture, it is important to use dilute nitric acid rather than sulphuric or hydrochloric for the carbonate test

Answer 35

If sulphuric acid is used, sulphate ions are added and will show up in the sulphate test If hydrochloric acid is used, chloride ions are added, and will sharp in the halide test.

Question 36

What is the purpose of a Barium meal

Answer 36

Coats inner lining of gut which will show up on x-ray - as it is insoluble (BaSO4 with water is taken) Barium is usually toxic, but it doesn't interact with the body due to BaSO4 being so insoluble