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A-Level Chemistry > Chapter 8 > Flashcards

Chapter 8 Flashcards

1
Q

Elements in group 2

A

Alkaline earth metals that are reactive and do not occur in elemental form naturally - stable compounds like CaCO3

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2
Q

Why are the group 2 eleemnts reducing agents?

A

2 electrons in outer s sub shell that are lost to fomr 2+ ion - they act as reducing agents because the 2 electrons produced can be gained by smother species to reducd them. Eventually end up with electron config as a noble gas with each metal atom being oxidised

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3
Q

Grouo 2 reaction with oxygen

A

Forms metal oxide n; magneisum burns with a brilliant white light. Metal is oxidised - total changed balance out to net 0 ; totsl reduction and oxidation = 0.

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4
Q

Redox reactions with water

A

React with water to form sn slkaline hydroxide and hydrogen gas - reactivity increases down the group ghus reacfions get more and more vigorous

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5
Q

Redox reactions with dilute acids

A

Metal + acid - > salt + hydrogen ; reactivity increases down the group

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6
Q

Why does reactivity increase down group 2?

A

Requires first two ionisation energies ; both of which decrease going down the group because attrcation between nucleus and outer elecgrons decfeases as a result of increasing atomic radius and increasing shielding

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7
Q

Group 2 oxides + water

A

Releasing hydroxide ions and forming an alkaline solution of metal hydroxide
CaO + H2O -> Ca2+ (aq) + 2OH- (aq)
Griuo 2 hydroxides are only slightly soluble in watsr and when solution is saturated any further metal and hydroxide ions will form a solid precipitate
Ca2+ (aq) + 2OH- (aq) -> Ca(OH)2 (s)

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8
Q

Solubility of group 2 hydroxides

A

Increases down the group so the resulting solutions contain more OH- ions and are more alkaline; Mg(OH)2 us on,y slightly so,uble thus low alkaline Ph (10)
Ba(OH)2 is mcuh more soluble with greater OH- ion concentration and thus ph higher (13)

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9
Q

Group 2 compounds in agriculture

A

Calcium hydroxide is added to fields as lime by farmers to increase the pH of acidic soils - calcium hydroxide neytralised acid in the soil forming neutral water
Ca(OH)2 + 2H+ -> Ca2+ (aq) + 2H2O (l)

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10
Q

Grouo 2 compounds in medicine

A

Used as antacids for treating acid indigestion sith mang indigestion tablegs containg magnesium and calcium carbonates as main ingredients - milk of magnesia is a suspension of white magnesium hydroxide Mg(OH)2 in water ; acid in stomach is mainly HCl and thus neutralksation reaction takes place

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11
Q

Halogens

A

Do not appear in elementsl form - as negatively charged ions dissolved in sea water for example

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12
Q

Trends in boiling points

A

Increases down the group as there are more electrons thus stringer london forces so more energy required to break these intermolechlsr forces so boiling point increases

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13
Q

Fluorine

A

Pale yellow gas

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14
Q

Chlorine

A

Pale green gas

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15
Q

Bromine

A

Red brown liquid

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16
Q

Iodine

A

Shiny grey black solid

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17
Q

Astatine

A

Never been seen radioactive - decays rapidly

18
Q

Redox reactions with halogens

A

5 electrons in outer p subshell - each halogen atom is reduced gaining an electron to form 1- ion
Cl2 + 2e- -> 2Cl-
Hallgens are the oxidising agent as another species js oxidised as a result of the hallgens losing electrons

19
Q

Hallgen halide displacement reactions

A

Reactivity of hallgens decreases down the group - solution of each halogen added to halides ; if more reacfive than halogen displaces halide and solution changes colour to the halogen that is left

20
Q

Solutions if halogens in water

A 
Chlorine = pale green
Bromine = orange
Iodine = brown
21
Q

Why is cyclohexane added?

A

Non-polar solvent with non polar hallgens disslving mlre readily - easjer to tell apart anf clntrast
Cl2 = pale green
Bromine = orange
Iodine = purp,e

22
Q

Ionic equation of halogen halid reactions?

A

ALL AQUEOUS SOLUTIONS

23
Q

Redox in halogen halide reactions

A

Halogen js reduced

Halide ion is oxidised

24
Q

Fluorine and astatine?

A

Fluorine is too reactive with any substance

Astatine very rare and decays rapidly

25
Q

Trend in reactivity

A

Halogens become less reactive down the group - atomic radius increases, more inner shells so shielidng increases thus less nuclear attraction to capture an electon from another species so reactivity decreases

26
Q

Halogens as oxidisng agents?

A

Become weaker oxidising agents down the griup eith fluorine the best

27
Q

Disporportionation

A

Same element is both oxidised and reduced - examples are chlorine with water and soidum hydroxide

28
Q

Chlorine + water

A

Used in water purification - killing harmful bacteria
Cl2 + H2O -> HClO + HCl
Both reduced and oxidised
Chloric i acid actuallh kills bacteria + ClO- ions. Also acts as a weak bleach (the chloric acid) ; indicator turns res first snd then is bleached

29
Q

Chlorine + aqueous sodium hydroxide

A

Cl2 (aq) + 2Na(OH (aq) -> NaClO (aq) + NaCl (aq) + H2O (l)

ClO- ions are used as a household bleach

30
Q

Benefits and risks of chlorine use

A

Chlorine is an extremely toxic fas and is a respiratory irritant in small concebtrations - chlorine in drinking water dab react with organic hydrocarbons such as methance which coud cause cancer. However this is outweighed by risk of not adding chlorine which could reshkt kn typhoid/cholera

31
Q

Precipitate reactions with aqueous silver ions

A

Ag+ (aq) + X- (aq) -> AgX (s)

Precipitage formed

32
Q

Qualititave analysis

A

Observation rather than measurements

33
Q

Carbonate tes

A

React wjth acuds to form CO2 gas - add dilute notric acid and id bubbles are seen then could be carbonage ; bubble gas through kimewater (calcium hydroxide) which then produces a cloudy lrecipitate of calcium carbonate

34
Q

Sulfate test

A

Barkum sulfate is insoluble in water - add aqueous barium ions to the sulfate ions and if BaSO4 is produced a solid precipitate is creafed which is white. USE BARIUM NITRATE AS WITH BARIUM CHLORIDE YOU INTRODUCE HALIDE IONS + MAKE SURE IT IS NOT CARBONATE BY GETTING RID OF CARBONATE

35
Q

Halide tests

A 
Silver halides are insoluble # aqueous silver ions react with halide ions to form precipitates of silver balides. Add silver nitrate 
Silver chloride - white
Silver bromjde - cream
Silver iodiide - yellow
Add ammonia
Dilute ammonia dissolves chloride
Conc smmonia dissolves bromide
Iodide does not dissolve in either
ALL AQUEOUS EXCEPT PRECIPITATE
36
Q

Sequence of tests

A

Carbonate
Sulfate
Halides

37
Q

Carbonate test sequence

A

Looking for effervescene from carbon dioxide gas - neither sukfate nor hakide jons bubbles with acid thus you can carry out carbonat test eithout possibility of an incorrect conclusion ; no carbonate present then move onto next

38
Q

Sulfate test sequence

A

Barium carbonate is also a white insoluble precipitae like baroum sulfate thus make shre to do carbonate first and kn,y proceed if no carbonates are present

39
Q

Halide test sequence

A

Silver ions are introduced -they can form a pfecipirate with carbonate and sukfate which is indoluble therefore carry it out last as the other two rule out any possibilities

40
Q

A mixture of ions

A

1) Carbonate ions - if bubbles are seen add in nitric acid until it stops ; all carbknate ions removed and nond left ; USE HNO3 AND NOT H2SO4/HCL AS IT CONTAINS SULFATE IONS
2) Sulfate test - no carbknates left ; add exceek barium nitrate will form a white precipiratet ; filter out the barium sulfafe. Dont use BACL2 due to halide ions
3) Halide test - add AgNO3 ; anh carbonate or sulfate removed so only halide left and add NH3 to confirm (aqueous)

41
Q

Test for am,onium ions

A

Add sodium hydroxide to form nh3 gas and water ; then heat and ammonium gas released ; use ph indicator paper should turn it fromr ed to blue (alkaline)

A-Level Chemistry (28 decks)

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