Chapter 8

Question 1

Elements in group 2

Answer 1

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

Question 2

Why are the group 2 eleemnts reducing agents?

Answer 2

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

Question 3

Grouo 2 reaction with oxygen

Answer 3

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.

Question 4

Redox reactions with water

Answer 4

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

Question 5

Redox reactions with dilute acids

Answer 5

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

Question 6

Why does reactivity increase down group 2?

Answer 6

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

Question 7

Group 2 oxides + water

Answer 7

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)

Question 8

Solubility of group 2 hydroxides

Answer 8

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)

Question 9

Group 2 compounds in agriculture

Answer 9

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)

Question 10

Grouo 2 compounds in medicine

Answer 10

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

Question 11

Halogens

Answer 11

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

Question 12

Trends in boiling points

Answer 12

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

Question 13

Fluorine

Answer 13

Pale yellow gas

Question 14

Chlorine

Answer 14

Pale green gas

Question 15

Bromine

Answer 15

Red brown liquid

Question 16

Iodine

Answer 16

Shiny grey black solid

Question 17

Astatine

Answer 17

Never been seen radioactive - decays rapidly

Question 18

Redox reactions with halogens

Answer 18

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

Question 19

Hallgen halide displacement reactions

Answer 19

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

Question 20

Solutions if halogens in water

Answer 20

Chlorine = pale green
Bromine = orange
Iodine = brown

Question 21

Why is cyclohexane added?

Answer 21

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

Question 22

Ionic equation of halogen halid reactions?

Answer 22

ALL AQUEOUS SOLUTIONS

Question 23

Redox in halogen halide reactions

Answer 23

Halogen js reduced

Halide ion is oxidised

Question 24

Fluorine and astatine?

Answer 24

Fluorine is too reactive with any substance

Astatine very rare and decays rapidly

Question 25

Trend in reactivity

Answer 25

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

Question 26

Halogens as oxidisng agents?

Answer 26

Become weaker oxidising agents down the griup eith fluorine the best

Question 27

Disporportionation

Answer 27

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

Question 28

Chlorine + water

Answer 28

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

Question 29

Chlorine + aqueous sodium hydroxide

Answer 29

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

ClO- ions are used as a household bleach

Question 30

Benefits and risks of chlorine use

Answer 30

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

Question 31

Precipitate reactions with aqueous silver ions

Answer 31

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

Precipitage formed

Question 32

Qualititave analysis

Answer 32

Observation rather than measurements

Question 33

Carbonate tes

Answer 33

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

Question 34

Sulfate test

Answer 34

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

Question 35

Halide tests

Answer 35

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

Question 36

Sequence of tests

Answer 36

Carbonate
Sulfate
Halides

Question 37

Carbonate test sequence

Answer 37

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

Question 38

Sulfate test sequence

Answer 38

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

Question 39

Halide test sequence

Answer 39

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

Question 40

A mixture of ions

Answer 40

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)

Question 41

Test for am,onium ions

Answer 41

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)