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A level Chemistry > Module 3: Reactivity Trends (Chapter 8) > Flashcards

Module 3: Reactivity Trends (Chapter 8) Flashcards

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1
Q

Why are group 2 known as reducing agents?

A

Have 2 outer electrons, which fill the outer s2 sub shell. In a reaction the metal atom is oxidised losing 2 electrons to form 2+ ions. Another species gains these 2 electrons, and is said to be reduced.

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2
Q

What is the most common type of reaction with group 2?

A

Redox reactions

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3
Q

Redox with group 2 metal and oxygen

A

Form a metal oxide with general formula MO.
Reactivity increases down the group due to increased atomic radius and shielding, so reduced nuclear attraction, meaning outer electrons can be lost more easily, and so form oxides faster

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4
Q

Redox with group 2 and water

A

Form a metal hydroxide with general formula M(OH)2 and H2

Reactivity increases down the group.

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5
Q

Redox with group 2 and dilute acids

A

Forms a salt and H2 gas

Reactivity increases down the group

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6
Q

What happens to the ionisation energy for group 2? What does this indicate about reactivity?

A

Ionisation energy decreases down the group
Reactivity increases down the group
Increased atomic radius and shielding
Decreased nuclear attraction
Less energy required to remove the outer electrons

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7
Q

Group 2 oxides and water reaction

A

Releases hydroxide ions
Forms alkaline solutions of metal hydroxides
Only slightly soluble in water
Saturated solution leads to the formation of precipitates

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8
Q

What happens to alkalinity down the group, and therefore solubility?

A

Solubility increases down the group, because they are more strongly alkaline as the metal hydroxides become more stable
High OH- concentration down the group
pH increases and therefore so does alkalinity

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9
Q

Group 2 in agriculture

A

Ca(OH)2 used as lime powder on acidic soil by farmers, to neutralise the soil.
Ca(OH)2 + 2H+ = Ca2+ + 2H2O

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10
Q

Group 2 in medicine

A

Used as antacids for treating acid indigestion
Mainly use Mg and Ca carbonates
‘Milk of Magnesia’ is a suspension of white Mg(OH)2 in water

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11
Q

Issue with Mg solubility

A

Low solubility in water

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12
Q

Neutralisation equations for Mg(OH)2 and CaCO3

A

Mg(OH)2 + 2HCl = MgCl2 + 2H2O

CaCO3 + 2HCl = CaCl2 + H2O + CO2

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13
Q

What are the halogens known as?

A

Diatomic molecules

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14
Q

Boiling point trend in the halogens

A

More electrons down the group
Stronger London forces
More energy needed to overcome strong intermolecular forces
Boiling point increases down the group

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15
Q

What outer shell electronic configuration do the halogens have?

A

s2p5

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16
Q

What is the most common reaction for halogens?

A

Redox - each halogen is reduced, gaining 1 electron to form a 1- halide.

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17
Q

Equation for reduction of halogen (Cl as example)

A

Cl2 + 2e- = 2Cl-

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18
Q

What are halogens known as?

A

Oxidising agents because they oxidise another species

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19
Q

Trend in reactivity of halogens

A

Reactivity decreases down the group
Atomic radius increases
Shielding increases
Less nuclear attraction to capture an electron from another species

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20
Q

Colour of halides in water

A 
Cl2 = pale green
Br2 = orange
I2 = brown
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21
Q

Colour of halides in cyclohexane

A 
Cl2 = pale green 
Br2 = orange 
I2 = violet / purple
22
Q

What proves reactivity decreases down the group?

A

Displacement reactions

23
Q

How are bromine and iodine distinguished between when added tp water?

A

Cyclohexane used or another non-polar solvent. Non-polar halogens dissolve more readily than in water.

24
Q

Cl and Br colour

A

Orange - Cl more reactive

25
Q

Cl and I colour

A

Purple - Cl more reactive than I

26
Q

Br in I colour

A

Purple - Br more reactive than I

27
Q

Define disproportionation

A

Redox reaction where the same element is both oxidised and reduced

28
Q

Chlorine and water reaction

A

Purifies water
Cl2 + H20 = HClO +HCl
Disproportionation of Cl
Bacteria killed by chloric(I) acid and chlorate ions (ClO-)

29
Q

What else in chloric(I) acid sued for?

A

Weak bleach - indicator paper shows this

30
Q

Chlorine with NaOH

A 
Cold, dilute aqueous sodium hydroxide
More chlorine dissolves - not limited by low solubility of chlorine in water
Disproportionation
Cl2 + 2NaOH = NaClO + NaCl + H2O 
ClO- ions in high concentration 
Used as household bleach
31
Q

Benefits of chlorine

A

Water treatment to ensure it is safe to drink and bacteria are killed
Prevents compromised drinking against cholera and typhoid
Controlled process

32
Q

Risks of chlorine use

A

Extremely toxic gas - respiratory irritant in small concentrations and fatal in high concen.
Can react with organic hydrocarbons like methane from decaying vegetation - chlorinated hydrocarbons form which are carcinogenic

33
Q

Describe the carbonate test

A

Add dilute nitric acid to a test tube containing the solution being tested
Effervesence can mean a carbonate
Bubble this through limewater

34
Q

Equation for carbonate test

A

Na2CO3 + 2HNO3 = 2NaCO3 + CO2 + H2O

35
Q

Equation for reaction of limewater with CO2

A

CO2 + Ca(OH)2 = CaCO3 + H2O

36
Q

Describe the sulfate test

A

Most sulfates are soluble in water but BaSO4 is very insoluble. White precipitate of barium sulfate is basis. Barium ions are added to solution.
Barium ions added as barium chloride or barium nitrate.
Barium nitrate if hakide test being completed after

37
Q

Equation for barium sulfate formation

A

Ba 2+ + SO4 2- = BaSO4

38
Q

Describe the halide test

A

Add aqueous silver nitrate to aqueous solution of halide
Silver halide precipitates at different colours
Add aqueous ammonia to trst solubility of precipitate and better distinguish between colours of halides

39
Q

Chloride precipitate colour

A

White

40
Q

Bromide precipitate colour

A

Cream

41
Q

Iodide precipitate colour

A

Yellow

42
Q

General equation for silver halide formation

A

Ag+ + X- = AgX

43
Q

Chloride and ammonia reaction

A

Dilute ammonia - soluble colourless solution

44
Q

Bromide and ammonia reaction

A

Concentrated ammonia - soluble colourless solution

45
Q

Iodide and ammonia reaction

A

Concentrated ammonia - insoluble yellow solution remains

46
Q

What is the seqeunce of tests?

A

Carbonate
Sulfate
Halide

47
Q

Why carbonate test first?

A

Only one to produce effervesence

48
Q

Why sulfate test second?

A

Barium carbonate is white and insoluble as well so the same result will emerge giving a false positive sulfate test. Only do if no carbonate present

49
Q

Why halide test last?

A

Silver carbonate and silver sulfate are both insoluble in water and will form precipitates. Rule out possibility of carbonate or sulfate present

50
Q

Describe the test for ammonia

A

Warm aqueous sodium hydroxide addded to solution of ammonium ion
Ammonia gas is produce - soluble in water so effervesence not seen
Heat mixture and gas is released
Test using damp indicator paper - alkaline so turns blue

A level Chemistry (14 decks)

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