Topic 4: inorganic chemistry and the periodic table

Question 1

State and explain the trend in MP going down group 2 metals

Answer 1

MP decreases. themetallic bond weaks as the atomic size increases. electrostatic attraction between the positive ions and the delocalised electrons decreases therefore less energy needed to break the bonds.

Question 2

State and explain the trend in 1st ionisation energy going down group 2

Answer 2

1st ionisation energy decreases. atoms are getting larger and therefore the outermost electrons are further from the nucleus and more shielded, decreasing the attraction between the nucleus and the electrons therefore less energy needed to remove the outer electrons.

Question 3

state the trend in reactivity going down group 2 metals

Answer 3

reactivity increases down the group as its easier to lose the electrons

Question 4

magnesium + oxygen

Answer 4

2Mg + O2 -> 2MgO
MgO is a white solid with a high mp due to its ionic bonding
Mg burns with a bright white flame

Question 5

when using magnesium ribbon, why do you need to clean it before use

Answer 5

magnesium reacts slowly with oxygen without a flame. therefore the magnesium ribbon will have a thin layer of magnesium oxide on it.
if testing for reaction rates with Mg and acid, the Mg and MgO would react at different rates, giving false results
MgO + HCl-> MgCl2 + H2O

Question 6

magnesium + steam

Answer 6

Mg + H2O(g) -> MgO + H2

bright white flame

Question 7

magnesium + warm water

Answer 7

Mg + 2H2O -> Mg(OH)2 + H2

much slower reaction than with steam and no flame

Question 8

group 2 metals + cold water products

Answer 8

froms the hydroxide (aq) + H2 (g)

Question 9

observations when group 2 metals react with hydroxides and trends in the reaction going down the group

Answer 9

fizzing (morevigorous down group)
the metal dissolves(faster down the group)
solution heats up (more down the group)

Question 10

calcium + cold water observation

Answer 10

a white precipitate appears (less precipitate forms down the group)

Question 11

group 2 oxides are ionic/basic?

Answer 11

basic as the oxide ions accept protons to become hydroxide ions (when reacting with water)

Question 12

groups 2 oxides + water products

Answer 12

just the hydroxide (s)
reaction with Mg gives pH9, with calcium gives pH12. This is because magnesium is only slightly soluble in water so fewer free OH- produced

Question 13

group 2 oxides + acid

Answer 13

-> salt (aq) + water

Question 14

groups 2 hydroxides + acids

Answer 14

-> salt (aq) + water
Eg
Mg(OH)2 (aq) + 2HNO3 (aq) -> Mg(NO3)2 (aq) + 2H2O(l)

Question 15

solubility of group 2 hydroxides

Answer 15

become more soluble down the group

Question 16

all group 2 hydroxides when not soluble appear as __

Answer 16

white precipitates

Question 17

how is magnesium hydroxide used in medicine

Answer 17

in suspension as milk of magnesia to neutralise excess acid in the stomach and to treat constipation.
it is safe to use because it is so weakly alkaline. more preferable to use than calcium carbonate as it will not produce CO2

Question 18

calcium hydroxide use in agriculture

Answer 18

neutralise acidic soils

Question 19

how can an aqueous solution of calcium hydroxide be used to test for CO2

Answer 19

aqueous solution of calcium hydroxide is limewater.
limewater turns cloudy as the white calcium carbonate is produced.
Ca(OH)2 (aq) + CO2 -> CaCO3 (s) + H2O (l)

Question 20

barium hydroxide + water ionic equation

Answer 20

Ba(OH)2 (s) + aq -> Ba2+ (aq) + 2OH- (aq)

Question 21

solubility of group 2 sulfates

Answer 21

group 2 sulfates become less soluble going down the group

Question 22

why does barium metal react slowly with sulfuric acid

Answer 22

insoluble barium sulfate produced will cover the surface of the metal and act as a barrier to further attack
same effect does not happen with other acids like HCL or HNO3 as they form soluble group 2 salts

Question 23

thermal decomposition of group 2 carbonates

Answer 23

group 2 carbonates become more thermally stable going down the group. as cations get bigger they have less of a polarising effect and distort the carbonate less therefore the C-O bond is weakened and more energy needed to break it.

Question 24

what is the group 1 carbonate that is the exception and will decompose

Answer 24

lithium carbonate

lithium ion is small enough ot have a polarising effect on the carbonate ion. it has a big enough charge density

Question 25

is it easier or harder to thermally decompose group 2 carbonates going down the group

Answer 25

going down the group it gets harderto thermally decompose them

Question 26

define thermal decomposition

Answer 26

the use of heat to break down a compound into more than one product

Question 27

MgCO3 (s) ->

Answer 27

MgO (s) + CO2 (g)

Question 28

how would you investigate thermal stability of group 2 carbonates

Answer 28

heata known mass of carbonate in a side arm boiling tube pass the gass produced through limewater time for limewater to go cloudy

Question 29

thermal decomposition of group 2 nitrates (V)

Answer 29

becomes harder to decompose going down the group they decompose to produce group 2 oxides and nitrogen dioxide gas (lithium nitrate decomposes the same as group 2 nitrates)

Question 30

observation when decomposing group 2 nitrates

Answer 30

``` brown gas (NO2) whitenitrate solid is seen to melt to a colourless solution and then re solidify ```

Question 31

equation for thermal decomposition of magnesium nitrate

Answer 31

2Mg(NO3)2 -> 2MgO + 4NO2 +O2

Question 32

how do group 1 nitrates, with the exception of lithium nitrate decompose

Answer 32

decompose to give a nitrate (III) salt and ocygen | 2NaNO3 -> 2NaNO2 + O2

Question 33

flame test

Answer 33

nichrome wire clean by dipping inot conc HCL dip into solid and then into blue flame observe colour change

Question 34

explain flame tests

Answer 34

an excited electron is promoted to a higher energy level by the heat from the flame when the electron drops to a lower energy level, energy is released in the from of visible light

Question 35

why is there no flame colour with magnesium

Answer 35

energy emitted of a wavelength outside visible spectrum

Question 36

appearance of halogens at room temp

Answer 36

fluorine- very pale yellow gas, highly reactive chlorine- greenish, reactive gas, poisonous in high conc bromine- red liquid, it gives off dense brown/orange poisonous fumes iodine- dark grey solid, sublimes to purple gas

Question 37

trend in MP and BP of halogens down the group

Answer 37

increases down the group | molecules are larger, more electrons, larger London forces, more energy needed to overcome the intermolecular forces

Question 38

trend in electronegativity of halogens

Answer 38

going down the group, the EN decreases | atomic radii increases, nucleus is less able to attract the bonding pair of electrons

Question 39

define electronegativity

Answer 39

electronegativity is the relative tendency of an atom in a molecule to attract electrons in a covalent bond to itself

Question 40

oxidising strength of halogens down the group

Answer 40

oxidising strength decreases down the group- harder to accept electrons

Question 41

potassium bromide + chlorine ionic eq

Answer 41

Cl2(aq) + 2Br- (aq) -> 2Cl- (aq) + Br2 (aq)

Question 42

potassium iodide + chlorine ionic eq

Answer 42

Cl2 (aq) + 2I- (aq) -> 2Cl- (aq) + I2 (aq)

Question 43

potassium iodide + bromine ionic eq

Answer 43

Br2 (aq) + 2I- (aq) -> 2Br- (aq) + I2 (aq)

Question 44

halogen + metal reactions- what is oxidsed

Answer 44

the metals are oxidised | Br2 (l) + 2Na(s) -> 2NaBr (s)

Question 45

reaction between chlorine/ bromine with iron (II)

Answer 45

iron (II) is oxidised to (III) | Cl2 (g) +2Fe2+ (aq) -> 2Cl- (aq) + 2Fe3+ (aq)

Question 46

reaction between iodine and iron (II)

Answer 46

iodine is not a strong oxidising agent to oxidise iron (II) to iron (III). the reaction is reversed 2I- (aq) + 2Fe3+ (aq) -> I2 (aq) + 2Fe2+ (aq)

Question 47

define disproportionation

Answer 47

a reaction where an element is simultaneously oxidised and reduced

Question 48

chlorine + water

Answer 48

disproportionation | Cl2 (g) + h2o(l) -> HClO (aq) +HCl (aq)

Question 49

observations with chlorine + water disproportionation reaction

Answer 49

adding universal indicator will first turn it red due to acidity of both reaction products. then turns colourless as HCLO bleaches the colour

Question 50

useof chlorine

Answer 50

usedin water treatment. used to treat drinking water and water in swimming pools

Question 51

reaction of aqueous halogens with cold dilute NaOH solution

Answer 51

Cl2 9aq) +2NaOH (aq) ->NaCl (aq) + NaClO (aq) +H2O (l) | mixture of NaCl and NaClO is used as bleach and to disinfect/kill bacteria

Question 52

reaction of halogens with hot dilute NaOH solution

Answer 52

disproportionation occurs but the halogen is oxidised | 3Cl2 (aq) +6NaOH(aq) -> 5NaCl (aq) +NaClO3 (aq) +3H2O (l)

Question 53

explain trend in reducing power of HALIDES going down the group

Answer 53

increasing reducing power down the group they have a greater tendency to donate electrons as ions get bigger so attraction between nucleus ans the outer electrons decreases

Question 54

sulfuric acid+ fluoride/chloride

Answer 54

no redox reaction occurs as the sulfuric acid is not strong enough to oxidise the halides. acid base reactions occur NaF (s) + H2SO4 (l) -> NaHSO4 (s) +HF(g) HF is white steamy fumes

Question 55

sulfuric acid + bromide

Answer 55

after the intial acid bas step, bromide reduces the sulfur in H2SO4 from 6+ to 4+ in SO2 acid basestep: NaBr(s) + H2SO4(l) -> NaHSO4 (s) +HBr (g) redox step: 2HBr + H2SO4 -> Br2 (g) +SO2(g) +2H2o (l) in first step sulfuric acid acts as an acid but in 2nd step acts as an oxidising agent as itgets reduced

Question 56

observations of sulfuric acid + bromide

Answer 56

in acid base step: white steamy fumes of HBr | in redox step: red fumes of Br2 (g) and a colourless, acidic gas SO2 (g)

Question 57

iodide + sulfuric acid (4 steps)

Answer 57

NaI(s) + H2SO4 (l) -> NaHSO4 (s) +HI 2HI + H2SO4 -> I2 (s) + SO2(g) +2H20 (l) 6HI + H2SO4 -> 3I2 + S (s) + 4H2O(l) 8HI + H2SO4 -> 4I2 (s) + H2S (g) + 4H2O (l)

Question 58

oxidation numbers of sulfur when reacting with iodide

Answer 58

+6 in H2SO4 to +4 in SO2 to 0 in S to -2 in H2S

Question 59

observations with iodide and sulfuric acid

Answer 59

``` HI gives white steamy fumes black solid and purple fumes of I2 colourless acidic gas of SO2 yellow solid of sulfur bad egg smell gas H2S ```