halogens (grp 7)

Question 1

what do halogens exist as

Answer 1

diamonic molecules

Question 2

appearance of fluorine

Answer 2

yellow gas

Question 3

appearance of chlorine

Answer 3

green gas

Question 4

appearance of bromine

Answer 4

brown liquid

Question 5

appearance of iodine

Answer 5

grey crystalline solid

Question 6

explain the increase in atomic radius down the group

Answer 6

more shells
shielding increases
more electrons

the pull the outer electrons feel from the nucleus is weaker with increasing number of shells

Question 7

define electronegativity

Answer 7

power of an atom to attract 2 electrons in a covalent bond

Question 8

explain electronegativity down the group

Answer 8

decreasing - larger atomic radius, more shells, more shielding, weaker attraction

Question 9

explain the trend in melting point and boiling point down the group

Answer 9

as molecules become larger they have more electrons and so have larger vdw forces between molecules

more energy needed to break these forces

increases melting and boiling point down the group

Question 10

solubility of halogens

Answer 10

halogens are poorly soluble in water. halogen molecules are non-polar and cannot form bonds with hydrogen bonds with water molecules

Question 11

what are halogens soluble in?

Answer 11

organic compounds

Question 12

colour of chlorine in water and in organic solvent

Answer 12

light yellow, pale yellow-green

Question 13

colour of bromine in water and in organic solvent

Answer 13

orange, red-brown

Question 14

colour of iodine in water and in organic solvent

Answer 14

brown, purple

Question 15

halogens trend in bond strength

Answer 15

decreases bc atomic radius increases

Question 16

what is bond enthalpy

Answer 16

heat needed to break one mole of a covalent bond

Question 17

why does fluorine have such low bond enthalpy

Answer 17

because fluorine is so small that the lone pairs get so close and cause repulsion counteracting the attraction between the bonding pair of electrons and two nuclei.

Question 18

why do you think no value for solubility is assigned to fluorine

Answer 18

reacts too violently to water

Question 19

how do halogens react with metals

Answer 19

by accepting an electron from the metal atom to become an ion with 1- charge

Question 20

how are halogens oxidising agents

Answer 20

halogens oxidise the metal by removing an electron from the metal

halogens become reduced as they gain the extra electron

Question 21

trend in oxidising power in halogens

Answer 21

decreases going down the group as their ability to attract electrons decreases due to shielding

Question 22

how do halide ions act as reducing agents

Answer 22

they get oxidised and lose electrons

Question 23

trend of reducing power of halide ions

Answer 23

they increase going down the group because atoms are more bigger with more shielding so its easier to lose an electron

Question 24

reaction of fluorine and chlorine with sulfuric acid

Answer 24

not strong enough to reduce s in h2so4

Question 25

one sodium halide that will reduce concentrated sulfuric acid

Answer 25

NaI (sodium iodide)

Question 26

one way H2S can be recognised

Answer 26

smell of rotten eggs

Question 27

one way to recognise sulfur

Answer 27

yellow solid

Question 28

a reagent which could be used to show the reducing ability of bromide ions is diff to chloride ions

Answer 28

sulphuric acid

Question 29

equation for dilute aqueous sodium hydroxide and chlorine & uses

Answer 29

CL2 + NaOH -> NaCl + NaOCl + H2O - bleach - kills bacteria

Question 30

equation for chlorine being added to drinking water

Answer 30

Cl2 + H2O -> HCl + HClO

Question 31

why is chlorine added to drinking water & name a disadvantage

Answer 31

- kills bacteria BUT - may cause eye irritation - taste bad

Question 32

equation for phosphorus TRU bromide

Answer 32

6Br2 + P4 -> 4PBr3

Question 33

test a sample of water to show it contains chloride ions

Answer 33

silver nitrate it would show white precipitate

Question 34

In terms of electron transfer, what is the meaning of oxidising agent

Answer 34

electron acceptor

Question 35

State what you would observe when chlorine gas is bubbled into an aqueous solution of potassium iodide.

Answer 35

brown solution

Question 36

Identify two sulfur-containing reduction products formed when concentrated sulfuric acid oxidises iodide ions

Answer 36

S & SO2

Question 37

Describe what you would observe when aqueous silver nitrate is added to separate aqueous solutions of potassium fluoride and potassium bromide

Answer 37

KF - no change KBR - cream precipritate

Question 38

Explain why bromine does not react with aqueous chloride ions

Answer 38

because Br2 is a weaker oxidising agent

Question 39

Write an equation to show how solid potassium fluoride reacts with concentrated sulfuric acid.

Answer 39

KF + H2SO4 -> KHSO4 + HF

Question 40

reaction of iodine with concentrated Sulfuric acid

Answer 40

1) H2SO4 + 2NaI -> HI + NaHSO4 2) H2SO4 + 2HI -> I2 + *SO2* + H2O 3) 6HI + H2SO4 -> 3I2 + *S* + 4H2O 4) 8HI + H2SO4 -> 4I2 + H2S + 4H2O