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Chemistry module 3 mine > Group 2&7 and tests > Flashcards

Group 2&7 and tests Flashcards

1
Q

solubility of group 2 hydroxides

A

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

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2
Q

ionisation energies down the group

A

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

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3
Q

why is ca(oh)2 added to fields

A

increase the pH of acidic soils

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4
Q

group 2 bases used as medicines?

A

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

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5
Q

colour of Ca flame

A

red/orange

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6
Q

colour of Sr flame

A

red

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7
Q

colour of barium flame

A

pale green

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8
Q

colour of Mg flame

A

white

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9
Q

state of bromine at RTP

A

orange-brown liquid

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10
Q

state of iodine at RTP

A

shiny grey black solid

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11
Q

state of chlorine at RTP

A

pale green gas

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12
Q

Usual reaction of halogens

A

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

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13
Q

Boiling point of halogen down the group

A 
decreases as:
- more electrons
- stronger London 
  forces
- more energy needed 
  to break IMF 
- boiling point 
  increases
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14
Q

colour of chlorine in solution in water

A

pale green

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15
Q

colour of bromine in solution in water

A

orange

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16
Q

colour of iodine in solution in water

A

brown

17
Q

why is cyclohexene added to water solutions

A

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

18
Q

colour of bromine in cyclohexene

A

orange

19
Q

colour of iodine in cyclohexene

A

violet

20
Q

trend in reactivity down the gorup

A 
- atomic radius 
  increases
- more inner shells so 
  shielding increases
- less nuclear 
  attraction to capture 
  electron from 
  another species
- reactivity decreases
21
Q

Halogens are….. agents

A

halogens - oxidising agents

flourine is the strongest oxidising agent

22
Q

Purpose of chlorine in water purification

A

Kills pathogen to avoid disease

Chlorine reacts with water to form acidic solution that kills pathogens

23
Q

Chlorine and water reaction

A

Forms

hydrochloric acid

Chloric acid (HOCl)

24
Q

Why is Cl2 reaction with H2O disproportionation reaction

A

Chlorine is both oxidised and reduced

Oxidised on HOCl
Reduced in HCl

25
Q

Risks of using chlorine to purify water

A

Gas is toxic

Chlorinated hydrocarbon may form which are carcinogenic

26
Q

Benefits of Chlorine purifying water

A

Kills many harmful microorganisms

Reduces rates of waterborne disease; cholera and typhoid

27
Q

How is bleach created

A

Cl2 and cold dilute NaOH

Forms NaOCl and NaCl

NaOCl is the bleach

28
Q

qualitative tests can test for:

A
  • carbonates
  • sulfates
  • halides
29
Q

carbonate test

A

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

30
Q

sulfate test

A
  • Barium ions are added to unknown compound BaNO3

- Forms BaSO4 which is insoluble and is therefore a white ppt

31
Q

Equations for Sulfate test. (2)

A

eg BaNO3 + XSO4 = BaSO4 + XNO3

Ionic: Ba2+ + SO4 2- = BaSO4 (s)

32
Q

Describe the test for halide ions.

Including ionic equation.

A
  • 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

33
Q

Describe the test for ammonium ions. (3)

A
  • 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.
34
Q

Ionic equation for ammonium test.

A

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

35
Q

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

A
  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.

Chemistry module 3 mine (4 decks)

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