[C4] Chemical changes

What is oxidation?

The gain of oxygen

What is reduction?

The loss of oxygen

Write a word equation for the reaction of metals with oxygen

metal + oxygen → metal oxide

How do metals form ions?

They lose electrons to form positively charged ions

What charge do metal ions have?

Positive

Why is potassium more reactive than copper?

Potassium has a stronger tendenacy to form positive ions than copper

Why is potassium more reactive than magnesium?

Potassium has a stronger tendenacy to form positive ions that magnesium

What non metals are often included in the reactivity series?

hydrogen and carbon

What is the order of the reactivity series?

potassium, sodium, lithium, calcium, magnesium, aluminium, zinc, iron, copper, silver, gold

What is a displacement reaction?

A reaction in which a more reactive metal takes the place of a less reactive metal from a compound

Why can calcium can displace copper from copper sulfate?

Calcium is more reactive than copper

Why can't magnesium displace potassium from potassium nitrate?

magnesium is less reactive than potassium

What is an ore?

A compound in which a metal is naturally found

Why are metals like gold found naturally occuring in the Earth?

Gold is unreactive and so doesn't react with other elements to form compounds

How are metals less reactive than carbon extracted from compounds?

Reduction with carbon

Why can carbon be used to extract iron from iron oxide?

carbon is more reactive than iron

"Which element is oxidised / reduced in the reaction:

copper oxide + carbon → carbon dioxide + copper"

oxidised = carbon, reduced = iron

[𝗛𝗶𝗴𝗵𝗲𝗿 𝘁𝗶𝗲𝗿] What is oxidation in terms of electrons?

Oxidation is the loss of electrons

[𝗛𝗶𝗴𝗵𝗲𝗿 𝘁𝗶𝗲𝗿] What is reduction in terms of electrons?

Reduction is the gain of electrons

Write a word equation for the reaction of acids with metals

Acid + metal → salt + hydrogen

What state is hydrogen at room temperature?

gas

What is a base?

A substance with a pH of greater than 7. Examples include metal hydroxides and metal oxides

What is an alkali?

A base that dissolves in water to release hydroxide ions and form a solution with a pH of greater than 7

What is the formula of nitric acid?

HNO₃

What is the formula of sulfuric acid?

H₂SO₄

What is the formula of hydrochloric acid?

HCl

What type of substance is a soluble metal hydroxide?

Alkali

What type of substances are insoluble metal hydroxides and metal oxides?

Bases

Write a word equation for the reaction of an acid with an alkali

Acid + alkali → salt + water

Write a word equation for the reaction of an acid with a base

Acid + base → salt + water

What pH do salts have?

7

Write a word equation for the reaction of a metal hydroxide with an acid

metal hydroxide + acid → salt + water

Write a word equation for the reaction of a metal oxide with an acid

metal oxide + acid → salt + water

What type of salts does hydrochloric acid produce?

chlorides

What type of salts does sulfuric acid produce?

sulfates

What type of salts does nitric acid produce?

nitrates

What is the formula of sodium hydroxide?

NaOH

What is the formula of magnesium oxide?

MgO

What is the formula of copper oxide?

CuO

Write a word equation for the reaction of metal carbonates with acids

metal carbonate + acid → salt + water + carbon dioxide

How can you tell that a gas is produced when metal carbonates react with acids?

bubbles can be seen

What is the formula of a nitrate ion?

NO₃⁻

What is the formula of a sulfate ion?

SO₄ ²⁻

What is the formula of a chloride ion?

Cl⁻

What is an aqueous solution?

The mixture formed when a substance dissolves in water

What ion do acids release when in aqueous solutions?

Hydrogen ions (H⁺)

What colour do strong acids turn universal indicator?

Red

What colour do weak acids turn universal indiactor?

Yellow

What colour do neutral substances turn universal indiactor?

Green

What colour do weak alkalis turn universal indicator?

Blue

What colour do strong alkalis turn universal indicator?

Purple

What ions do alkalis release when in aqueous solutions?

Hydroxide ions (OH ⁻)

What does the pH scale range from?

0-14

What is the pH of a neutral substance?

7

What pH do acids have?

0-6

What pH do alkalis have?

8-14

Describe how water is produced in a neutralisation reaction

The hydrogen ions from the acid react with the hydroxide ions from the alkali to produce water

What is the ionic equation for neutralisation reactions?

H⁺ (aq) + OH ⁻ (aq) → H₂O (l)

What is pH?

A measure of hydrogen ion concentration

What is a neutralisation reaction?

A reaction between an acid and an alkali to produce salt and water

What does soluble mean?

A solid that dissolves

How can a soluble salt be made?

- React an acid with an insoluble solid (e.g metals, metal oxide, metal hydroxide or metal carbonate) - Add the insoluble solid to the acid in excess (until no more dissolves) - Remove the excess solid by filtering to produce a solution of the salt - Heat the salt solution over water until the volume of the salt solution is halved - Leave to cool and crystalise

𝙒𝙝𝙚𝙣 𝙥𝙧𝙚𝙥𝙖𝙧𝙞𝙣𝙜 𝙖 𝙨𝙤𝙡𝙪𝙗𝙡𝙚 𝙨𝙖𝙡𝙩: Why is the insoluble solid added in excess to the acid?

To make sure all the acid reacts

𝙒𝙝𝙚𝙣 𝙥𝙧𝙚𝙥𝙖𝙧𝙞𝙣𝙜 𝙖 𝙨𝙤𝙡𝙪𝙗𝙡𝙚 𝙨𝙖𝙡𝙩: Why is the acid warmed?

To speed up the reaction

𝙒𝙝𝙚𝙣 𝙥𝙧𝙚𝙥𝙖𝙧𝙞𝙣𝙜 𝙖 𝙨𝙤𝙡𝙪𝙗𝙡𝙚 𝙨𝙖𝙡𝙩: What safety precautions should you take?

Wear safety googles

𝙒𝙝𝙚𝙣 𝙥𝙧𝙚𝙥𝙖𝙧𝙞𝙣𝙜 𝙖 𝙨𝙤𝙡𝙪𝙗𝙡𝙚 𝙨𝙖𝙡𝙩: Why is the mixture of the insoluble solid and salt solution filtered?

To remove any of the unreacted insoluble solid

𝙒𝙝𝙚𝙣 𝙥𝙧𝙚𝙥𝙖𝙧𝙞𝙣𝙜 𝙖 𝙨𝙤𝙡𝙪𝙗𝙡𝙚 𝙨𝙖𝙡𝙩: Why is the salt solution heated over water instead of heating it directly over a bunsen burner?

Heating over water is more gentle and helps to prevent the salt crystals breaking down

Why is a burette used during titrations?

To add small, measured volumes of one reactant to the other reactant

What are titres?

The volume of one reactant needed to react completely with the other reactant in a titration

What is the end point of a titiration?

What the indicator just changes colour

What are concordant titres?

Results that are within 0.1 cm³ of eachother

What indicators could be used for titrations?

Methyl orange or phenolphthalein

Why is universal indicator not used in titrations?

There is not a clear end point

[𝗛𝗶𝗴𝗵𝗲𝗿 𝘁𝗶𝗲𝗿] What type of acid is completely ionised in aqueous solutions?

strong acids

[𝗛𝗶𝗴𝗵𝗲𝗿 𝘁𝗶𝗲𝗿] What type of acid is only partially ionised in aqueous solutions?

weak acids

[𝗛𝗶𝗴𝗵𝗲𝗿 𝘁𝗶𝗲𝗿] Give examples of strong acids

hydrochloric, nitric and sulfuric

[𝗛𝗶𝗴𝗵𝗲𝗿 𝘁𝗶𝗲𝗿] Give examples of weak acids

ethanoic, citric and carbonic

[𝗛𝗶𝗴𝗵𝗲𝗿 𝘁𝗶𝗲𝗿] As the pH decreases by one unit (e.g. from 4 to 3) what happens to the hydrogen ion concentration?

hydrogen ion concentration increases by a factor of 10

[𝗛𝗶𝗴𝗵𝗲𝗿 𝘁𝗶𝗲𝗿] What is a dilute acid?

An acid that contains a low concentration of acid particles and a high concentration of water molecules

[𝗛𝗶𝗴𝗵𝗲𝗿 𝘁𝗶𝗲𝗿] What is a concentrated acid?

An acid that contains a high concentration of acid particles and a low concentration of water molecules

[𝗛𝗶𝗴𝗵𝗲𝗿 𝘁𝗶𝗲𝗿] What is a strong acid?

An acid that is completely ionised in aqueous solution

[𝗛𝗶𝗴𝗵𝗲𝗿 𝘁𝗶𝗲𝗿] What is a weak acid?

An acid that is only partially ionised in aqueous solution

[𝗛𝗶𝗴𝗵𝗲𝗿 𝘁𝗶𝗲𝗿] How many more hydrogen ions are there in an acid with pH of 4 than an acid of pH of 5

10 times more

[𝗛𝗶𝗴𝗵𝗲𝗿 𝘁𝗶𝗲𝗿] The greater the concentration of hydrogen ions the ______ the pH

lower

Why can ionic compounds not conduct electricity when solid?

The ions are not free to move

Why can ionic compound conduct electricity when molten or aqueous?

The ions are free to move

What is an electrolyte?

An ionic compound that is aqueous or molten and so able to conduct electricity

What is a cation?

A positvely charged ion

What is an anion?

A negatively charged ion

What charge is the cathode?

Negative

What charge is the anode?

Postive

What ions move towards the cathode?

Positively charged ions (cations)

What ions move towards the anode?

Negatively charged ions (anions)

Why do positively charged ions move towards the cathode?

The cathode is negatively charged and opposite charges attract

Why do negatively charged ions move towards the anode?

The anode is postively charged and opposite charges attract

What is the produced at the cathode when aqueous solutions undergo electrolysis?

If the metal is more reactive than hydrogen, then hydrogen gas (H₂) is produced, if the metal is less reactive than hydrogen then the metal is produced

What is produced at the anode when aqueous solution undergo electrolysis?

If halide ions are present (group 7 ions), then the halogen is produced. If not then oxygen (O₂) is produced

What is bauxite?

Aluminium oxide (Al₂O₃)

Why is cryolite added when aluminium oxide (bauxite) undergoes electrolysis?

Lower the melting point