inorganic chemistry

what is the name given to group 1 elements

alkali metals

describe the physical characteristics of group 1 metals

• soft (can be cut with a knife)

• low melting and boiling points

• low density (floats on water)

• shiny (tarnishes when exposed to air)

describe the chemical properties of group 1 elements

• reacts vigorously with water to form metal hydroxides like NaOH

• reacts with oxygen to form metal oxides eg. Li₂O

  • eg. 4Li + O₂ —> 2Li₂O

• form ionic compounds like NaCl

• react with halogens like KCl

why do all group 1 elements have similar chemical properties?

all have one electron in their outer shell

describe the observations when lithium is added to water

• fizzes gently

• moves across surface of water

• disappears

describe the observations when sodium is added to water

• melts and forms a ball

• fizzes

• moves across surface of water

• gets smaller and disappears

• leaves a white trail

describe the observations when potassium is added to water

• melts and forms a ball

• fizzes vigourously and explodes

• sparks

• burns with a lilac flame

• leaves a white trail

what are the similarities of the reactions of lithium and potassium with water?

they both float, effervesce, move around on the surface of the water and disappear

what are the differences of the reactions of lithium and potassium

lithium fizzes gently but potassium explodes

lithium doesn’t burn but potassium has a lilac flame

lithium doesn’t melt but potassium melts into a ball

what is the word equation for when group 1 metals are added to cold water

metal + water → metal hydroxide + hydrogen

what’s the balanced symbol equation for when sodium is added to cold water

2Na + 2H₂O —> 2NaOH + H₂

why do group 1 metals fizz on contact with water?

hydrogen gas released

what colour would universal indicator turn if present when a g1 metal is added to water?

purple

• metal hydroxide produced

• hydroxides are alkalis

how should g1 elements be stored and why?

• in oil

• very reactive and lose properties eg shininess very quickly

what are the reactions of g1 metals with air?

lithium burns with a red flame to form lithium oxide

sodium burns with a yellow flame to form sodium oxide

potassium burns with a lilac flame to form potassium oxide

predict the properties of francium

g1 element

• soft low melting and boiling point low density shiny and tarnishes when exposed to air

near bottom of g1

• reactions with air and water will be more violent than other g1 metals

give the state and colour of g7 elements at room temp

fluorine = gas, yellow

chlorine = gas, green

bromine = liquid, red-brown

iodine = solid, grey (forms purple vapour when heated

describe the trends in the physical properties of the halogens

colour gets darker down the group

boiling point and melting point increase down the group

reactivity decreases down the group

all poor conductors of heat and electricity

describe the reactions of halogens with hydrogen

- Hydrogen halides formed

- e.g. H₂ (g) + Br₂ (g) → 2HBr (g)

- Hydrogen halides are acidic and highly poisonous

- Very soluble in water

- e.g. hydrogen chloride gas dissolves to form hydrochloric acid

- HCl (g) → HCl (aq)

predict the state and colour of astatine

below iodine in periodic table

solid

dark grey/black

what is a displacement reaction

when a more reactive halogen displaces a less reactive halide from its compound

halogen displacement reactions

give the ionic equation of the displacement reaction between Cl2 and KBr

- Overall reaction: Cl2 (aq) + 2KBr (aq) → 2KCl (aq) + Br2 (aq)

- Separate out ionic compounds

- Cl₂ (aq) + 2K+ (aq) + 2Br- (aq) → 2K+ (aq) + 2Cl- (aq) + Br₂ (aq)

- Remove spectator ions that appear on both sides (i.e. 2K+)

- Ionic equation: Cl₂ (aq) + 2Br- (aq) → Br₂ (aq) + 2Cl- (aq)

Why are three of the reactions not carried out in the above table?

- A halogen cannot displace itself

- No reaction would occur

Why do three of the experiments not produce a reaction?

A halogen cannot displace a more reactive halogen

Describe two experiments to show the order of reactivity of bromine, chlorine and iodine

- Add chlorine (Cl2) to KBr

- Solution turns orange

- Cl₂+ 2KBr → Br₂+ 2KCl

- Add bromine (Br2) to KI

- Solution turns brown

- Br₂+ 2KI → l₂+ 2KBr

Name the gases present in the air and their approximate percentage by volume

- Nitrogen 78% - Oxygen 21% - Argon 0.96% - Carbon dioxide 0.04%

Describe how copper can be used to show the percentage of oxygen in the air

- Copper is put in a large tube that is attached to two gas syringes

- One syringe contains 100cm3 of air

- One syringe empty (pushed all the way in)

- Copper heated strongly

- Air passed over copper using syringes

- Oxygen reacts with copper

- Forms copper (II) oxide (CuO)

- Air allowed to cool

- Volume of air decreases to 80cm3

Explain why the copper between the syringes turns black

- Copper reacts with oxygen

- Forms copper (II) oxide

- 2Cu (s) + O2 (g) → 2CuO (s)

why is the air allowed to cool before measuring the change in volume?

gas expands when heated

describe how iron can be used to show the percentage of oxygen in the air

iron filing placed in a burette that is full of air

end of burette placed in a trough of water

iron reacts with oxygen

water moves into burette

how is the percentage of oxygen in the air calculate using the iron filings experiment

initial column of air height/final column of air height x 100

describe how phosphorus can be used to show the percentage of oxygen in the air

phosphorous placed on a tray inside a tube full of air

tube placed in a beaker of water

phosphorous lit with hot wire

phosphorous reacts with oxygen in the air

phosphorous + oxygen → phosphorous oxide

4P + 5O₂ —> P₄O₁₀

volume of air decreases

water moves into tube, pushing phosphorus up

Describe the observations when magnesium burns in oxygen

bright white light

white solid forms

magnesium + oxygen = magnesium oxide

2Mg (s) + O₂(g) → 2MgO (s)

Give the word and symbol equation for when magnesium oxide dissolves in water

- Magnesium oxide + water → magnesium hydroxide

- MgO (s) + H₂O (l) → Mg(OH)₂ (aq)

forms an alkaline solution

describe the observations when hydrogen burns in oxygen

pale blue flame

water forms

2H₂ (g) + O₂ (g) → 2H₂O (l)

describe the observations when sulfur burns in oxygen

blue flame

poisonous colourless sulfer dioxide gas forms

S (s) + O₂ (g) → SO₂

sulfur dioxide dissolves in water to form acidic solution of sulfurous acid

SO₂ (g) + H₂O (l) → H₂SO₃ (aq)

what type of reaction are combustion reactions

oxidation reactions

a substance gains oxygen

define thermal decomposition

breaking down of a substance using heat

what type of reaction occurs when metal carbonates are heated?

thermal decomposition

describe the thermal decomposition of copper 2 carbonate

copper II carbonate is a green solid

it decomposes to form copper oxide- a black solid

give word and symbol equations for the reaction that occurs when copper II carbonate is heated strongly

Copper(II) carbonate → copper (II) oxide + carbon dioxide

- CuCO₃ → CuO + CO₂

Explain the effect on the environment of increasing atmospheric levels of carbon dioxide

Greenhouse gas → contributes to global warming

- Polar ice caps melt - Sea levels rise - Floods low lying land - Loss of habitats and biodiversity

What is the reactivity series?

List of metals in order of their reactivity - Most reactive metals at the top - Least reactive at the bottom

How can you determine the reactivity of a metal?

Place in cold water (most will not react)

- those which react are the most reactive metals

- If no reaction, test with steam

- If no reaction, test with acid

(note: only metals above hydrogen in the reactivity series will react with acid)

- Note: Potassium, sodium, lithium and calcium are too reactive to react with acids (dangerous)

Explain how displacement reactions can be used to arrange metals in order of reactivity

- Occur when a less reactive element is pushed out of its compound by a more reactive element

- e.g. with metals and metal oxides:

- Magnesium + copper (II) oxide → magnesium oxide + copper

- Displacement reaction occurred, therefore magnesium more reactive than copper

- e.g. with metals and aqueous solutions of metal salts:

- Zinc + copper (II) sulfate → zinc sulfate + copper

- Displacement reaction occurred, therefore zinc more reactive than copper

what is the reactivity series

Give the word and symbol equation for when iron rusts

Iron + oxygen + water → hydrated iron (III) oxide

- 4Fe + 3O₂ + nH₂O → 2Fe₂O₃.nH₂O

what conditions are needed for rusting

water

oxygen

what methods are used to prevent iron from rusting

barrier methods

galvanising

sacrificial protection

how do barrier methods prevent iron from rusting

Provide protective layer

- Prevent water / oxygen reaching iron

- e.g. paint (bridges), grease (car engines), oil (bike chains)

- If the layer is damaged the iron will rust

Describe the process of galvanising

Coating iron in a more reactive metal

e.g. zinc - Zinc reacts with oxygen first, forming Zn2+

- Zn loses electrons instead of iron

- Used for car bodies, buckets

What is sacrificial protection?

- Method used to stop iron from rusting

- Iron coated in a more reactive metal / blocks of more reactive metal attached to iron

- More reactive metal undergoes oxidation in preference to iron

Define oxidation

Gain of oxygen - Loss of electrons

Define reduction

- Loss of oxygen

- Gain of electrons

Define redox

A reaction where both reduction and oxidation take place at the same time

Define oxidising agent

- Something which causes another substance to be oxidised

- An oxidising agent is itself reduced (it gains electrons)

Define reducing agent

-Something which causes another substance to be reduced

- A reducing agent is itself oxidised (it loses electrons)

Describe how to investigate reactions between dilute acids and metals

- Pour the same volume of a dilute acid into four boiling tubes

- Place a small piece of different metals (e.g. magnesium, zinc, iron, copper) in each tube

- Observe the changes that occur:

- A rapid fizzing and a colourless gas (hydrogen) produced

- Reaction mixture becomes warm as heat is produced (exothermic)

- More reactive metal = more fizzing and more heat

Explain why hydrogen gas is produced when a metal reacts with a dilute acid

- Metals above hydrogen in reactivity series will react with dilute acids

- Produce a salt and hydrogen in a displacement reaction

- e.g. magnesium + hydrochloric acid → magnesium chloride + hydrogen

- Mg (s) + 2HCl (aq) → MgCl2 (aq) + H2 (g)

Methyl Orange

Red in acid

Yellow in alkaline

Phenolphthalein

Colourless in acid

Pink in alkaline

Litmus paper

Red in acid

Blue in alkaline

Universal indicator

Red in acid

Purple in alkaline

What ion is responsible for making something acidic?

- H+

- Produced by acids in aqueous solutions

What ion is responsible for making something alkaline?

- OH-

- Produced by alkalis in aqueous solutions

Define acid

- H+ donor

Define base

- H+ acceptor

- OH- donor

- e.g. metal carbonate, hydroxide, oxides, ammonia

Define alkali

- Soluble base

What is a neutralisation reaction

- Addition of a base to an acid

- To produce a neutral solution

What is a salt

- Ionic compound formed by the neutralisation of an acid by a base

Give the ionic equation for a neutralisation reaction

- H+ + OH- → H2O

Remembering which ionic compounds (salts) are soluble/insoluble:

- All sodium, potassium and ammonium compounds are soluble

- All nitrates are soluble

- All sulfates are soluble except lead (II) sulfate, barium sulfate, and calcium sulfate

- All chlorides are soluble except lead (II) chloride and silver chloride

- All carbonates are insoluble except ammonium, potassium and sodium salts

- All hydroxides are insoluble except ammonium, potassium and sodium salts

- Calcium hydroxide is slightly soluble

Provide an example of the Brønsted-Lowry theory in context

- Dissolving hydrogen chloride in water

- H2O(l) + HCl(aq) → H3O+(aq) + Cl- (aq)

- HCl donates H+ (acts as an acid)

- H2O accepts H+ (acts as a base)

Which compounds can act as bases?

- Metal oxides / hydroxides

- Ammonia

Describe the reactivity of metals with acids

- Metals below hydrogen in the reactivity series do not react with acids

- Metals above hydrogen in the reactivity series react with acids, producing hydrogen

- Note: very reactive metals react very explosively with acids e.g. Potassium

How do you make soluble salts?

- Use the crystallisation method

- REACT until saturated

- FILTER

- EVAPORATE: heat to evaporate some water

- COOL: collect crystals that form

- DRY: allow the crystals to dry in a warm place or on filter paper

- For the reactants, you can use:

- Acid + insoluble metal/metal oxide/metal hydroxide/metal carbonate

What is the test for hydrogen?

- Lit splint burns with squeaky pop

What is the test for oxygen?

Glowing splint relights

What is the test for carbon dioxide?

Limewater turns cloudy when gas bubbled through

What is the test for ammonia?

Damp red litmus paper turns blue

What is the test for chlorine?

- Bleaches damp blue litmus paper

How do you test for ammonium ions (NH4+)?

- Add sodium hydroxide solution

- No precipitate is formed, but choking gas is given off (ammonia)

- Turns damp red litmus paper blue - confirms presence of ammonia

How do you test for copper (Cu2+), iron (II) (Fe2+) and iron (III) (Fe3+)?

- Use precipitation reactions by adding sodium hydroxide

- Cu2+ → copper hydroxide, Cu(OH)2, produced = light blue precipitate

- Fe2+ → Iron(II) hydroxide, Fe(OH)2, produced = green precipitate

- Fe3+ → Iron(III) hydroxide, Fe(OH)3, produced = brown precipitate

How do you test for halides?

- Add dilute nitric acid

- Removes carbonate ions

- Add silver nitrate

- Silver halide precipitate forms

Results of adding silver nitrate to halides:

- Silver chloride = white precipitate

- Silver bromide = cream precipitate

- Silver iodide = yellow precipitate

- e.g. Ag+ (aq) + I- (aq) → AgI (s)

How do you test for sulfates?

- Add dilute hydrochloric acid (removes carbonate ions)

- Add barium chloride

- Result: barium sulfate is a white precipitate

- Ba2+ (aq) + SO42- (aq) → BaSO4 (s)

How do you test for carbonates?

- Add dilute hydrochloric acid

- Fizzing indicates carbon dioxide being produced

- Test for carbon dioxide using lime water

- Turns milky/cloudy

- 2H+ (aq) + CO32- (aq) → CO2 (g) + H2O (l)

What is the chemical test for water?

- White anhydrous copper sulfate turns blue

- Hydrated copper (II) sulfate formed = blue crystal

How do you do a physical test for water?

- Check boiling point

- Water boils at 100°C

How do you show that water is pure?

- Check boiling point

- Pure water has single boiling point at 100°C