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chemistry > C8 - Reactivity trends > Flashcards

C8 - Reactivity trends Flashcards

1
Q

What is group 2 called?

A

Alkaline earth metals

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2
Q

What are group 2 elements used as?

A

Reducing agents

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3
Q

What happens to group 2 elements during redox reactions?

A

Oxidised
Acts as a reducing agent

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4
Q

Half equation for redox reaction of group 2 metal

A

M –> M2+ + 2e-

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5
Q

What happens to the reactivity of group 2 metals down the group?

A

Increases

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6
Q

Equation for group 2 element plus water?

A

M + 2H2O –> M(OH)2 + H2

Metal + water —> metal hydroxide + hydrogen

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7
Q

What happens during redox reactions of group 2 metals and water?

A

Group 2 metal is oxidised
2 atoms of H reduced and other 2 do not change

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8
Q

Group 2 metal plus dilute acid

A

metal + acid –> salt + H2

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9
Q

What happens during redox reaction of group 2 metal and a dilute acid

A

Metal is oxidised
Hydrogen is reduced

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10
Q

Why does the reactivity of group 2 metals increase down the group?

A

Losing 2 e- and forming 2+ ions require input of first and second ionisation energies
Ionisation energies decrease down the group so are easier to overcome

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11
Q

Why do ionisation energies decrease down group 2?

A

Attraction between nucleus and outer shell electrons decrease:
-Increasing atomic radius
-Increasing shielding

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12
Q

What happens to the strength of reducing agents down group 2?

A

Increases

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13
Q

Group 2 oxides + water

A

MO + H2O –> M2+ + 2OH-
(when solution becomes saturated: M2+ + 2OH- –> M(OH)2)

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14
Q

What happens to the solubility and alkalinity of group 2 hydroxides down the group?

A

Increases

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15
Q

How can you show solubility and alkalinity of group 2 hydroxides increase down the group?

A

1) Add a spatula of each Group 2 hydroxide to water in a test tube
2) Shake mixture. You will have a saturated solution of each metal hydroxide and white precipitate.
3) Measure the pH of each solution

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16
Q

What are group 2 oxides, hydroxides and carbonates used for?

A

As a base, to neutralise acids

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17
Q

What are group 2 compounds used for?

A

Lime to neutralise soil
Antacids to treat indigestion

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18
Q

How are group 2 compounds used in agriculture?

A

Ca(OH)2 added to fields as lime to increase pH of acidic soils
Ca(OH)2 + 2H+ –> Ca2+ + 2H2O

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19
Q

How are group 2 compounds used in medicine?

A

Many antacids/indigestion tablets use Mg/CaCO3
Milk of magnesia is a suspension of white Mg(OH)2 in water

Mg(OH)2 + 2HCl –> MgCl2 + 2H2O
CaCO3 + 2HCl –> CaCl2 –> H2O + CO2

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20
Q

Is Mg(OH)2 soluble in water?

A

Only slightly

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21
Q

What is group 7 known as?

A

Halogens

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22
Q

What happens to boiling points down group 7?

A

Increases

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23
Q

How do group 7 elements exist at room temperature?

A

Diatomic molecules

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24
Q

Why do boiling points increase down group 7?

A

-More electrons
-Stronger London forces
-More energy required to break intermolecular forces
-Boiling point increases

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25
Q

How does fluorine exist at RTP?

A

Pale yellow gas

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26
Q

How does chlorine exist at RTP?

A

Pale green gas

27
Q

How does bromine exist at RTP?

A

Red-brown liquid

28
Q

How does iodine exist at RTP?

A

Shiny grey-black solid

28
Q

What happens to halogens during redox reactions?

A

Reduced, oxidising agents

29
Q

Half equation for halogens

A

X2 + 2e- –> 2X-

30
Q

How can you test the reactivity of halogens?

A

Halogen-halide displacement reactions

31
Q

What happens to the reactivity of halogens down the group?

A

Decreases

32
Q

How do you do a halogen-halide displacement reaction?

A

-Solution of each halogen is added aqueous solutions of the other two halides
-Halogen displaces halide causing solution to change colour
-Iodine and bromine in water can appear similar orange-brown colour
-Organic non-polar solvent (cyclohexane) added and mixture shaken
-Non-polar halogens dissolve more readily in cyclohexane and colour change occurs

33
Q

Reaction between chlorine water and bromide solution

A

Pale green to orange as Br2 formed
Cl2 + 2Br- –> 2Cl- + Br2

34
Q

Reaction between chlorine water and iodide solution

A

Pale green to violet as I2 formed
Cl2 + 2I- –> 2Cl- + I2

35
Q

Reaction between bromine water and chloride solution

A

No reaction

36
Q

Reaction between bromine water and iodide solution

A

Orange to violet from I2 formed
Br2 + 2I- –> 2Br- + I2

37
Q

Reaction between iodine water and chloride solution

A

no reaction

38
Q

Reaction between iodine water and bromide solution

A

No reaction

39
Q

How does astatine exist at RTP?

A

Radioactive, never been seen

40
Q

Why does the reactivity decrease down group 7?

A

-Atomic radius increases
-More inner shells so shielding increases
-Less nuclear attraction
-Reactivity decreases

41
Q

What happens to the oxidising ability down group 7?

A

Decreases

42
Q

What is disproportionation

A

Redox reaction in which the same element is both oxidised and reduced

43
Q

Reaction of chlorine with water

A

Cl2 + H2O –> HClO + HCl

44
Q

What is chlorine used for?

A

Water purification

45
Q

What is HClO called?

A

Chloric (I) acid

46
Q

How does chlorine purify water?

A

Chloric (I) acid and chlorate (I) ions kill bacteria

47
Q

Reaction of chlorine with cold, dilute sodium hydroxide

A

Cl2 + 2NaOH –> NaClO + NaCl + H2O

48
Q

What use does the reaction of chlorine with cold, dilute sodium hydroxide serve?

A

Household bleach

49
Q

What are the risks of chlorine use?

A

-Respiratory irritant and can be fatal
-Toxic gas
-Can react with organic hydrocarbons producing chlorinated hydrocarbons which may cause cancer

50
Q

Why is chlorine still used to purify water considering risks?

A

Risks of not adding chlorine to water are far greater

51
Q

What is the test for halide ions?

A

1) Add silver nitrate solution
2) Precipitate is formed
Ag+ + X- –> AgX

52
Q

What is the carbonate test?

A

Carbonate reacts with acids to form CO2
1) In a test tube, add dilute nitric acid to sample
2) If there is effervescence, could be a carbonate
3) Test for carbon dioxide by bubbling through Ca(OH)

53
Q

What is the test for carbon dioxide?

A

1) Bubble gas through limewater (saturated solution of Ca(OH)2)
2) Carbon dioxide reacts to form white precipitate of CaCO3, turning limewater cloudy

54
Q

What is a sulfate test?

A

1) Barium nitrate added to sample
2) If white precipitate formed, sulfate is present

55
Q

Ionic equation for formation of barium sulfate?

A

Ba2+ + SO42- –> BaSO4

56
Q

What is a halide test?

A

1) Add aqueous silver nitrate to sample
2) Halide precipitates are different colours
3) Add aqueous ammonia to test solubility of precipitate

57
Q

Halide test results

A

Chloride - white, soluble in dilute NH3
Bromide - cream, soluble in conc NH3
Iodide - yellow, insoluble in conc NH3

58
Q

What sequence do you carry out these tests?

A

1) Carbonate, CO3 2-
2) Sulfate, SO4 2-
3) Halides, Cl- Br- I-

59
Q

Why is carbonate test first

A

-Add a dilute acid, looking for effervescence
-Neither sulfate or halide ions bubble with dilute acids
-If test produces no bubbles, continue to next test

60
Q

Why is sulfate test 2nd

A

-Add solution containing Ba+ ions, forms white precipitate of BaSO4
-BaCO3 is also a white precipitate, so if sulfate test carried out on carbonate test will be positive
-So, test should be carried out when you know no carbonate is present

61
Q

Why is halide test last?

A

-Add solution containing Ag+ ions, looking for precipitate
-Both Ag2CO3 and Ag2SO4 are precipitates
-So test should be carried out last

62
Q

How do you test a mixture of ions?

A

1) Carbonate test
-Add dilute nitric acid until bubbling stops
-All carbonate ions would have then been removed
2) Sulfate test
-Add excess of Ba(NO3)2 to solution left
-Filter solution to remove BaSO4
3) Halide test
-Add AgNO3 to solution left
-Carbonate and sulfate ions removed so precipitates involve halides
-Add NH3 to confirm halids

63
Q

How do you test for an ammonium ion?

A

1) Aqueous NaOH added to solution of ammonium ions
2) Ammonia gas produced
3) Mixture is warmed and ammonia gas released
4) Test with moist pH indicator, should turn blue

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