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Alevel CHEM > Reacitvity Trends p > Flashcards

Reacitvity Trends p Flashcards

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1
Q

Physical properties of group 2

A

Reasonably high melting and boiling pants

Light metals with LOW densities

Form colourless white compounds

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2
Q

Ionisation energy - group 2

A

Decreases as you go down the group

More shielding, greater atomic radius

Ionisation energy decreases
MORE REACTIVE

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3
Q

Reducing agents - group2.

A

Each group2. Element has 2 outer shell electrons

Group 2 metals loose 2 electrons to a 2+ ion, the other species gain and is reduced

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4
Q

Redox reaction with oxygen (group 2)

A

React vigorously with oxygen to form a metal oxide ( general formula of MO)

2Mg + O2 — 2 Mg O

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5
Q

Redox reactions with water ( group2 )

A

React with water to form an alkaline hydroxide
General formula M( OH)2
Hydrogen gas formed
Be- doesn’t react

Mg + H20 —- Mg(OH)2 + H2

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6
Q

Redox reactions with dilute acids( group 2)

A

Form a salt and hydrogen gas
Exception of be

E.g. Mg + 2HCl— Mgcl 2 + H2

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7
Q

Group 2 oxides/hydroxides as bases?

A

Metals are bases( most are soluble so they’re alkalis too)

The group2 oxides react with H20=- metal hydroxides , which dissolve. Make the solution STRONGLY alkaline - releasing OH- ions

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8
Q

What is an exception for oxides of group2 metals

A

Magnesium oxide reacts SLOWLY and the hydroxide isn’t very soluble

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9
Q

What happens to the solubility fo hydroxides as you go down the group 2

A

Solubility INCREASES
Resulting solutions contain more OH- IONS, AND ARE more alkaline
Mg(OH)2 - slightly soluble in h20, the solution has a low OH- concentration and a ph of 10
Ba( OH)2 - more soluble in h20- solution has a greater OH- concentration and a ph - 13

SOLUBILTIY, PH AND ALKLAINITY INCREASES

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10
Q

Group2 compounds( bases) in agriculture

A 
Calcium hydroxide( Ca(OH)2), added to fields as lime my farmers to increase the Ph of acidic soils 
The calcium hydroxide neutralises acids in the soil forming water
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11
Q

Medicine - group2 compounds as bases

A

Group 2 bases often used for antacids for relating acid indigestion
Many indigestion tabs use magnetism hydroxidea nd calcium carbonates -

Acid in stomach = Hcl
Mg(OH)2 + 2HCl—– 2H20 + MgCL

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12
Q

The halogens- chlorine

A

Green gas, Poisionesss in high concentrations

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13
Q

Flurorine

A

Pale yellow gas

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14
Q

Bromine

A

Red liquid that goes off dense brown Poisionesss fumes

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15
Q

Iodine

A

Shiny grey solid - sublimes to purple gas

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16
Q

Trend in melting and boiling point - halogens

A

More electrons as you descend
Stronger London dispersion forces between the molecules
More energy required to break these intermolecular forces
Boiling point INCREASES

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17
Q

Trends in reactivity

A

Halogen atoms react by gaining an electon in p subs hell to form 1- ion
- they are REDUCED - oxidise another substance
- DESCENDING the group, atomic radius increases, outer electrons are further from the nucleus, outer shell electrons are also shielded move from the attraction of the positive nucleus because of inner electrons
Harder for large atoms to attract electron = less reactive

18
Q

Halogen- halide displacement, what happens hen a halogen is added to a halid in a solution

A

If the halogen is MORE reactive - reaction takes place,
Halogen displaces the halide for the solution

Chlorine displaces both bromine and iodine, but iodine doesn’t displace ether

19
Q

Chlorine in h20 and organic solvent?

A

Pale green

20
Q

Bromine in h20 and organic solvent?

A

Orange

21
Q

Iodine in water and organic solvent

A

Brown in h2o

Purple in organic solvent

22
Q

Fluorine

A

Pale yellow gas

Reacts with almost any substance

23
Q

Astatine

A

Rare

Radioactive - decays rapidly

24
Q

Disproportion - halogens

A

Redox reaction
Same element oxidised an deduced

Reaction of heroine wit h20 and cold, dilute sodium hydroxide

25
Q

Chlorine + sodium hydroxide

A

BLEACH

2NaOH+ Cl2 — NaClO + NaCl 2 + H20

26
Q

Chlorine+ water

A

Cl2+ h20 – Hcl+ Hcl0

Hcl0+ H20– Clo- + H30+
aqueous caloric acid ionises to make chlorite ions that kill bacteria

27
Q

Chronicled water- PROS

A

Kills disease-causing microorganism
Some chlorine remains in H20- prevents reinfect ion further down the supply
Prevents algae growth, eliminating bad smell and taste, removing discolouration caused by organic compiunds

28
Q

Cons of chlorinated water

A

Harmful if breathed in ( gas)- respiratory irritant
Liquid form = chemical burn
If reacts with organic compounds- chlorinated hydrocarbons( CANCER CAUSING)

29
Q

Alternatives to chlorinated water

A

Purification tablets

UV light- ineffective in cloudy water and won’t stop water being infected further own the line, BUT kills microorganism by DNA damaging

OZONE- Strong oxidising agent, kills microorganisms

30
Q

Carbonate ion?

A

CO3 … 2-

31
Q

Carbonate ion test

A

Add dilute acid e.g, Hcl to form CO2

Bubble the gas through lime water and it will turn CLOUDY( ca(Oh)2)

Co2 forms a fine white precipitate of calcium carbonate, whihc is what turns the water Cloudy
( carbonate+ acid– co2 and water)

32
Q

Sulphate ion?

A

So4 2-

33
Q

SULFATE ion test

A

Most Sulphates are soluble in water BUT barium sulphate is insoluble - forms a white precipitate

Add dilute Hcl( ensure carbonate ions are removed ) and barium chloride

Ba 2+. + SO4 2- ——-BaSO4

34
Q

Halide ions test

A

Most halides are soluble in h2o but silver halides are INSOLUBLE
Aqueous silver ions react with aqueous halide ions to produce precipitates of silver halides

Add aqueous silver nitrate( Ag No3) to an aqueous solution fo a halide add aqueous ammonia if the colour is hard to distinguish

35
Q

Chloride , bromine and iodine colours- halide test

A

Chlorine- white, soluble in dilute NH3

Bromine- cream, soluble in concentrated NH3

Iodine - yellow, insoluble in concentrated NH3

36
Q

Ammonia

A

Nh3

37
Q

Ammonium ions

A

NH4 +

38
Q

Ammonium ions test

A

Ammonia gas ( NH3) is alkaline, so you can check for it suing a damp piece of red litmus paper - turns it red

Add naOH and warm the mixture

NH4 + + OH- —– NH3 + H20

39
Q

False positives?

A

Barium carbonate is a white and insoluble in h20, Oslo if you carry out the SULFATE test on a carbonate, youll get a white precipitate too, barium sulphite = same m need to ensure there’s no carbonate first

Silver carbonate and silver sulphate are both insoluble in h20 - form as precipitates in. This test( AgNO3 forming white precipitate)

40
Q

Order of tests

A

Carbonate, sulphate then halide

41
Q

Mixture of ions - describe doing tests and why it works in this order

A
  1. CARBONATE test= if you see bubbles, continue adding dilute nitric acid until bubbling stops, all carbonate ions removed
  2. SULFATE test = add an excess of Ba(NO3)2, any sulphate ins present will precipitate as barium SULFATE- filter solution to remove
  3. HALIDE test= Add AgNO3, any carbonate or sulphate ions initially present have been removed

Alevel CHEM (13 decks)

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