Group 2&7 and tests

Question 1

solubility of group 2 hydroxides

Answer 1

solubility of the hydroxides in water increases down the group so solution has more OH- ions and is more alkaline

Question 2

ionisation energies down the group

Answer 2

decrease down, attraction between the nucleus and outer electrons decreases as increasing atomic radius and increased shielding
so reactivity increases down the group and stronger reducing agents down the group

Question 3

why is ca(oh)2 added to fields

Answer 3

increase the pH of acidic soils

Question 4

group 2 bases used as medicines?

Answer 4

used as anti acids to treat acid indigestion e.g. milk of magnesia Mg(OH)2

Question 5

colour of Ca flame

Answer 5

red/orange

Question 6

colour of Sr flame

Answer 6

red

Question 7

colour of barium flame

Answer 7

pale green

Question 8

colour of Mg flame

Answer 8

white

Question 9

state of bromine at RTP

Answer 9

orange-brown liquid

Question 10

state of iodine at RTP

Answer 10

shiny grey black solid

Question 11

state of chlorine at RTP

Answer 11

pale green gas

Question 12

Usual reaction of halogens

Answer 12

usually redox where halogen is reduced to increase outer electrons from 7 to 8

Question 13

Boiling point of halogen down the group

Answer 13

decreases as:
- more electrons
- stronger London 
  forces
- more energy needed 
  to break IMF 
- boiling point 
  increases

Question 14

colour of chlorine in solution in water

Answer 14

pale green

Question 15

colour of bromine in solution in water

Answer 15

orange

Question 16

colour of iodine in solution in water

Answer 16

brown

Question 17

why is cyclohexene added to water solutions

Answer 17

iodine and bromine colours are similar in water, cyclohexene added to tell them apart as iodine turns from brown to violet whereas bromine stays orange

Question 18

colour of bromine in cyclohexene

Answer 18

orange

Question 19

colour of iodine in cyclohexene

Answer 19

violet

Question 20

trend in reactivity down the gorup

Answer 20

- atomic radius 
  increases
- more inner shells so 
  shielding increases
- less nuclear 
  attraction to capture 
  electron from 
  another species
- reactivity decreases

Question 21

Halogens are….. agents

Answer 21

halogens - oxidising agents

flourine is the strongest oxidising agent

Question 22

Purpose of chlorine in water purification

Answer 22

Kills pathogen to avoid disease

Chlorine reacts with water to form acidic solution that kills pathogens

Question 23

Chlorine and water reaction

Answer 23

Forms

hydrochloric acid

Chloric acid (HOCl)

Question 24

Why is Cl2 reaction with H2O disproportionation reaction

Answer 24

Chlorine is both oxidised and reduced

Oxidised on HOCl
Reduced in HCl

Question 25

Risks of using chlorine to purify water

Answer 25

Gas is toxic Chlorinated hydrocarbon may form which are carcinogenic

Question 26

Benefits of Chlorine purifying water

Answer 26

Kills many harmful microorganisms Reduces rates of waterborne disease; cholera and typhoid

Question 27

How is bleach created

Answer 27

Cl2 and cold dilute NaOH Forms NaOCl and NaCl NaOCl is the bleach

Question 28

qualitative tests can test for:

Answer 28

- carbonates - sulfates - halides

Question 29

carbonate test

Answer 29

carbonates react with acids to form CO2 ``` - add dilute HNO3 to test tube with compound - bubble gas through limewater Ca(OH)2to see its CO2 , cloudy ``` CO2 + Ca(OH)2 --> CaCO3 +H20 caco3 turns water cloudy

Question 30

sulfate test

Answer 30

- Barium ions are added to unknown compound BaNO3 | - Forms BaSO4 which is insoluble and is therefore a white ppt

Question 31

Equations for Sulfate test. (2)

Answer 31

eg BaNO3 + XSO4 = BaSO4 + XNO3 Ionic: Ba2+ + SO4 2- = BaSO4 (s)

Question 32

Describe the test for halide ions. | Including ionic equation.

Answer 32

- Add AgNO3 to unknown solution - Precipitation reaction will form a Silver halide - X- + Ag+ = AgX - Colour of the ppt indicates the type of halide ion; White- Chloride Cream- Bromide Yellow- Iodide The further distinguish, NH3 is added; Dilute NH3 dissolves Cl- (more reactive) but not Br- Concentrated NH3 dissolves Br- NH3 dissolves iodine

Question 33

Describe the test for ammonium ions. (3)

Answer 33

- Add NaOH (aq) to the unknown solution. - NH3 gas should be produced but since it dissolves in water, it has to be heated to release the gas. - Test the gas released with pH indicator paper which should turn purple as ammonia is alkali.

Question 34

Ionic equation for ammonium test.

Answer 34

NH4+ + OH- = NH3(g) + H20(l)

Question 35

Explain the sequence of tests for all the qualitative analysis. (3)

Answer 35

1. ) Carbonate Test: other tests do not produce bubbles with dilute acid 2. ) Sulfate test: BaCO3 is also white ppt so CO3- test is before to ensure it is not that. 3. ) Halide test: Silver carbonate and sulfate are also insoluble ppt so the previous tests go first to eliminate those ions.