redox, group chemistry and periodicity

Question 1

what is oxidation

Answer 1

loss of electrons, leading to an INCREASE in oxidation number

Question 2

what is reduction

Answer 2

gain of electrons, DECREASE in oxidation number

Question 3

what is the oxidation number of an element

Answer 3

always 0

Question 4

what is the oxidation number of a simple ion

Answer 4

the charge

Question 5

what is the oxidation number of F (in a cpd)

Answer 5

always -1

Question 6

what is the oxidation number of O (in a cpd)

Answer 6

-2
except when:
*bonded to F
*in a peroxide ion (-1)

Question 7

what is the oxidation number of H (in a cpd)

Answer 7

+1
except when:
*bonded to a metal (-1)

Question 8

what is the oxidation number of Cl (in a cpd)

Answer 8

-1
except when:
*bonded to F/O/N

Question 9

what is the oxidation number of a compound/ complex ion

Answer 9

sum ox. numbers = overall charge

compounds are always 0

Question 10

what is the half equation for P to P³‐

is this oxidation or reduction

Answer 10

P + 3e- = P³‐

reduction

Question 11

what is the half equation for Na to Na+

is this oxidation or reduction

Answer 11

Na -> Na+ + e-

oxidation

Question 12

what is the trend in melting and boiling points down group 7 (the halogens) and why

Answer 12

melting and boiling points increase

because more electrons = stronger london forces

Question 13

what is the appearance of chlorine

Answer 13

green/yellow GAS

Question 14

what is the appearance of bromine

Answer 14

red/brown VOLITILE LIQUID

Question 15

what is the appearance of iodine

Answer 15

shiny black SOLID
purple vapour on heating
purple in an organic solvent

Question 16

what is the trend in reactivity DOWN group 7 (the halogens) and why

Answer 16

down the group, reactivity DECREASES

because as atomic radius increases, electron shielding increases, so there is less nuclear attraction and the ability to gain e- into a
p sub-shell decreases

Question 17

how do you test for halide ions?

Answer 17

add equal volume dil. nitric acid

add a few drops of silver nitrate (AgNO3) - if a halide is present a ppt will form

add dil. ammonia solution - if the halide is Cl- the ppt will dissolve

add conc. ammonia solution - if the halide is Br- the ppt will dissolve

if the ppt does not dissolve the halide is I-

Question 18

what colour ppt does Cl- form

Answer 18

white

Question 19

what colour ppt does Br- form

Answer 19

creamy

Question 20

what colour ppt does I- form

Answer 20

yellow

Question 21

why is nitric acid added when testing for halide ions

Answer 21

to remove any unwanted carbonate and hydroxide ions to prevent false positives

Question 22

what is disproportination

Answer 22

the simultaneous oxidation and reduction of the same species

Question 23

what are the benefits of using chlorine to treat water

Answer 23

• kills pathogens
• simple to use
• cheap

Question 24

what are the risks of using chlorine to treat water

Answer 24

• chlorine is toxic
• chlorinated hydrocarbons MAY form - these are carcinogenic (cause cancer)

PROS OUTWEIGH THE CONS

Question 25

what is produced when chlorine reacts with water at RTP

what is the equation for this

Answer 25

chloric(1) acid
Cl2 + H2O <=> HCl + HOCl
reversible reaction
disproportination, as Cl is both oxidized and reduced

Question 26

what is formed when Cl reacts with cold dilute sodium hydroxide
what is the equation for this

Answer 26

bleach - sodium hyperchlorate/ sodium chlorate
Cl2 +2NaOH -> NaCl + NaClO + H2O
disproportination, as Cl is both oxidized and reduced

Question 27

what is the trend in first ionization energy down group 2 and why

Answer 27

first ionization energy DECREASES down group 2
because:
*greater electron shielding due to more full energy levels
*greater atomic radius which reduces the attraction between the nucleus and outermost electron

Question 28

what is the trend in reactivity down group 2 and why

Answer 28

reactivity INCREASES down group 2

because first ionization energy decreases, so less energy is required for the outermost electron to be lost

Question 29

what is the trend in melting point down group 2 and why

Answer 29

melting point DECREASES down group 2 because atomic radius increases, causing a weaker attraction between the ions and weaker metallic bonding

Question 30

how do you test for CO3 ²‐ ions

Answer 30

add acid

turns lime water cloudy in a delivery tube (white ppt) as CO2 is formed

Question 31

how do you test for sulphate SO4²‐ ions

Answer 31

add HCl to remove unwanted carbonate ions

add Barium Chloride BaCl2

if SO4²‐ is present then BaSO4 is formed, forming a white precipitate

Question 32

how do you test for ammonium NH4+ ions

Answer 32

add sodium hydroxide NaOH
heat gently
hold damp red litmus paper over test tube
if NH4+ is present NH3 will be formed and the red litmus paper will turn blue

Question 33

what are the trends across period 3 and why

Answer 33

first ionization energy INCREASES across a period
because there are more protons in the nucleus, meaning electrostatic attraction increases. they all have the same number of shells so electron shielding is constant

electronegetivity INCREASES across a period
because there are more protons, leading to stronger attraction between the nucleus and the bonding pair of electrons

Question 34

what is periodicity

Answer 34

repeating trends in physical or chemical properties across a period