inorganic chem

Magnesium + oxygen

2Mg(s) + O2(g) → 2MgO(s)

• White solid formed

Strontium + oxygen

Sr(s) + O2(g) → SrO2(s)

• Strontium and barium react to form peroxides

Magnesium + cold water

Mg(s) + 2H2O(l) → Mg(OH)2(s) + H2(g)

Magnesium + steam

Mg(s) + H2O(l) → MgO(s) + H2(g)

• white solid and white light

Calcium oxide + water

CaO(s) + H2O(l) → Ca(OH)2(aq)

• colourless solution (basic)

Calcium oxide + sulphuric acid

CaO(s) + H2SO4(aq) → CaSO4(s) + H2O(l)

Strontium hydroxide and dilute hydrochloric acid

Sr(OH)2(s) + 2HCl(aq) → SrCl2(aq) +2H2O(l)

Thermal decomposition of calcium carbonate

CaCO3(s) → CaO(s) + CO2(g)

Limewater equation (calcium hydroxide and carbon dioxide)

Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l)

Thermal decomposition of calcium nitrate

2Ca(NO3)2(s) → 2CaO(s) + 4NO2(g) + O2(g)

• Toxic brown gas

Thermal decomposition of lithium nitrate

4LiNO3(s) → 2Li2O(s) + 4NO2(g) + O2(g)

Thermal decomposition of sodium nitrate

2NaNO3(s) → 2NaNO2(s) + O2(g)

what is formed in the reactions between halogens and (some) metals

metal halide salts, which are ionic compounds consisting of halogen anions and metal cations.

what is happening to the metals when reacting with halogens

the metal is being oxidised, so halogens are acting as oxidising agents

how do halogens (chlorine, bromine and iodine) react with iron (II)

chlorine and bromine oxidise iron(II) to iron(III), while iodine has a lesser oxidising ability. iodine is oxidised from iodide ions to iodine

give the ionic equation of chlorine oxidising iron (II)

Cl2(g) + 2Fe2+(aq) → 2Cl-(aq) + 2Fe3+(aq)

give the ionic equation for the reaction between iodine and iron (III)

2I-(aq) + 2Fe3+(aq) → I2(aq) + 2Fe2+(aq)

give the equation for the reaction between chlorine and water

Cl2(g) + H2O(l) ↔ HCl(aq) + HOCl(aq)

give the equation for the reaction between cold sodium hydroxide and chlorine

Cl2(aq) + 2NAOH(aq) → NaCl(aq) + NaClO(aq) + H2O(l)

give the equation for the reaction between hot, concentrated sodium hydroxide and chlorine

3Cl2(aq) + 6NaOH(aq) → NaClO3(aq) + 5NaCl(aq) + 3H2O(l)

how can the reducing power of halides be compared

by reacting them with concentrated sulphuric acid

what happens when a halide ion acts as a reducing agent

it loses electrons, given to the reduced species

what is the trend in reducing power down the group

reducing power increases down the group (I>Br>Cl>F)

why is sulphuric acid used to observe the reducing power of halides

as it can be reduced to many different oxidation states

what are the 4 species and their oxidation states containing sulphur

• H2SO4 → +6

• SO2 → +4

• S → 0

• H2S → -2

what happens during the test when concentrated sulphuric acid is added to solid samples of halide salts

NaX(s) + H2SO4(l) → HX(g) + NaHSO4(aq)

• acid-base reaction. concentrated acid means there are not many water molecules to fully dissociate, only one H+ ion is lost.

• HX(g) from reaction may reduce H2SO4 as gas bubbles through acid redox reaction where concentrated sulphuric acid acts as oxidising agent

what can the hydrogen halides (HBr, HCl and HI) be observed as

steamy fumes caused by HX gas reacting with water vapour in the air to produce a fog of concentrated HX acid

give the equation for the equation between NaCl and concentrated H₂SO₄ (1)

NaCl + H₂SO₄ → NaHSO₄ +HCl

what can be observed in the reaction between Cl^- ions and concentrated sulphuric acid

steamy fumes of HCl

give the equations between NaBr (Br- ions) and concentrated sulphuric acid (2)

NaBr + H2SO4 → NaHSO4 + HBr

2Br- + H2SO4 + 2H+ → Br2 + SO2 + 2H2O

what can be observed in the reaction of br- ions with concentrated sulphuric acid

• HBr - steamy fumes

• Br2 - brown fumes

• SO2 - colourless gas

give the equations for the reaction between NaI (I- ions) and concentrated sulfuric acid (4)

• NaI + H2SO4 → NaHSO4 + HI

• 2I- + H2SO4 + 2H+ → I2 + SO2 + 2H2O

• 6I- + H2SO4 + 6H+ → 3I2 + S + 4H2O

• 8I- + H2SO4 + 8H+ → 4I2 + H2S + 4H2O

what can be observed in the reaction between I- and concentrated H2SO4

• HI - steamy fumes

• I2 - purple fumes

• SO2 - colourless gas

• S - yellow solid

• H2S - gas (bad egg smell)

Give the balanced equation of the reaction between ammonia and hydrogen chloride

NH3(g) + HCl(g) ←→ NH4Cl(s)

What can be observed in the reaction between ammonia and hydrogen chloride

White smoke

What is the trend in melting/boiling points down the group

Increases due to increase in london dispersion forces

How does fluorine appear at room temp

Pale yellow gas

How does chlorine appear at room temp

Pale green/yellow gas

How does bromine appear at room temp

orange-brown liquid

How does iodine appear at room temp

Grey-black solid

What colour is bromine as a gas

Orange

What colour is iodine as a gas

Purple

How does chlorine appear in aqueous solution

Colourless/pale green

How does chlorine appear in organic solvents

Colourless/pale green

How does bromine appear in aqueous solution

Orange

How does bromine appear in organic solvents

Orange

How does iodine appear in aqueous solution

Yellowy-Brown

How does iodine appear in organic solvents

Purple

Why is the electronegativity of halogens significant

Halogens have high electronegativity meaning they are good oxidising agents. Going down the group, atoms get larger so it is harder to gain electrons (reactivity decreases down the group)

what is the trend in volatility down group 7

Volatility decreases down the group as molecular size increases, leading to stronger van der Waals forces.

what is the structure of halogens

exist as diatomic molecules so are simple molecular structures with weak London dispersion dories between them caused by instantaneous dipole-induced dipole forces

explain the trend in boiling point, melting point and volatility down group 7

the more electrons, the Greater London forces, therefore the larger the molecule, the stronger these forces between molecules. therefore, down the group, it gets more difficult to separate the molecules so boiling and melting points increase. it gets more difficult to separate the molecules so volatility of halogens decreases down the group.

what is the trend of electronegativity down the group

decreases down the group, therefore their oxidising power decreases going down the group.

which element in group 7 is the strongest oxidant agent

fluorine due to its high electronegativity and small atomic radius, allowing it to attract electrons more effectively than other halogens.

what is the trend in reactivity down group 7

reactivity decreases down the group due to increasing atomic size and shielding effect, making it harder for the larger atoms to attract electrons.

How do you carry out a flame test

• take a platinum/nichrome wire

• Dip into concentrated hydrochloric acid and then heat in bunsen flame until no colour is seen

• Dip wire into fresh concentrated hydrochloric acid then into metal salt

• Heat wire and sample in flame

Why do you use a nichrome/platinum wire?

They’re unreactive with the air in the flame and do not have their own flame colour

Why is the wire dipped into hydrochloric acid and then heated (the first time)

To clean the wire of any other previous samples

Why is the wire dipped in concentrated HCl then in the sample

It reacts with the salts to form chlorides which are more volatile as they have lower boiling points as they need to be in the gaseous state for the tests to work.

Li+

Red/crimson

Na+

Yellow

K+

Lilac

Rb+

Red

Cs+

Blue/violet

Be2+

Colourless

Mg2+

Colourless

Ca2+

Brick red

Sr2+

Red

Ba2+

Apple green

How do flame tests work

• electrons absorb the heat energy from the flame and move to higher energy levels

• Electrons drop back down to lower energy levels

• Light in visible region is released

• Different energy gaps between levels cause different colours

Why is CaO and CaCO3 used to remove sulphur dioxide from flue gas

Because CaO is a metal oxide so is basic. It reacts with the SO2 in an acid base reaction

What does strontium and barium react with oxygen to form

Strontium/barium peroxide (O-)

What is needed for Magnesium to react with oxygen, and what does it fo

Heat applied to form MgO (white solid)

How does magnesium react with cold water?

Slow reaction to form insoluble layer of magnesium hydroxide (Mg(OH)2)

How does magnesium react with steam (what can be observed)

Forms MgO. A white flame seen and white solid formed.

Why does Mg and H2O make MgO and not Mg(OH)2 as a final product when reacted with steam

When the hydroxide is formed, it undergoes thermal decomposition to form the oxide

What is the trend in reactivity down group 2

Increasing reactivity

What do calcium, strontium and barium react with cold water to form

Hydrogen and a hydroxide

What is the reaction between a group 2 metal oxide with water

Forms a hydroxide (no other products) - colourless solution

What is the reaction between a group 2 metal oxide and a dilute acid

Forms a salt and water (neutralisation/acid base reaction)

How do group 2 metal hydroxides react with a dilute acid

Forms a salt and water (eg Sr(OH)2 + 2HCl → SrCl2 + 2H2O

What is the trend of solubility of group 2 hydroxides down the group

Increasing solubility of hydroxides down the group

What is the trend of solubility of group 2 sulphates down the group

Decreasing solubility down the group (remember barium sulphate is insoluble - used for barium meals for x-rays)

How will the pH of a solution for the hydroxides change down the group and why

pH will increase (more basic) due to increased concentration of OH- ions

What does a CO3²- ion decompose to

O²- ion and CO2 gas

What does an NO3- decompose to

Smaller, stable NO-2 OR O2- and/or O2/NO2

What do group 2 metal carbonates decompose to form

The metal oxide and carbon dioxide gas

Explain the trend in thermal stability of carbonates down a group

• the ionic radius of the metal ion increases

• Charge density decreases

• Polarising power of metal ion/cation decreases

• Polarisation of carbonate ion decreases weakening the C-O bond less

• Meaning group 1 carbonates are more stable than group 2

• And group 2 carbonates get more stable down the group

What is the only unstable group 1 metal carbonate

Lithium

What is the experimental procedure to compare the thermal decomposition of carbonates

• heat sample of carbonate and bubble gas through limewater/gas syringe

• Fair test (use same flame/distance between sample and flame/volume of limewater/moles of sample)

• Record time taken for limewater to go cloudy

What forms when group 2 nitrates undergo thermal decomposition

Metal oxide, nitrogen dioxide and oxygen

How do you know if a group 2 nitrate has decomposed

• brown, toxic gas formed (NO2)

• Relights a glowing splint (O2)

• (White solid before and after - not showing how they decomposed)

What weird observations might be found with magnesium and calcium nitrates and why?

They normally have water of crystallisation so solid may dissolve in its own water - makes a colourless solution before it starts to decompose.

What do most group 1 nitrates (not lithium) decompose to form

Metal nitrate and oxygen

What does lithium nitrate decompose to form

Lithium oxide, nitrogen dioxide and oxygen

Why is lithium nitrate more thermally stable than magnesium nitrate

• Mg ion is smaller and more highly charged

• Mg ion has more polarising power

• Mg ion polarises nitrate ion more

• It weakens the N-O bonds in the nitrate ion more

What is the experimental procedure to compare the thermal decomposition of nitrates (+safety precaution)

• take equal amounts of solid nitrates in test tubes

• Heat equally record time taken to produce brown fumes/relight glowing splint

• Safety - use fume cupboard

What is the test for ammonium ions (NH4+)

1. Add NaOH

2. Gently heat

3. Test any gas produced with damp red litmus

What observations can be made from a positive test for NH+ ions

Damp red litmus turns red to blue

What are the reactions that take place during the test for ammonium ions (give equations)

• NH4+(aq) + OH-(aq) → NH3(g) + H2O(l)

• NH3(g) + H2O(l) → NH4+(aq) + OH-(aq)