AQA GCSE Chemistry Topic 4: Chemical Changes
4.4.1 Reactivity of metals
Extraction of metals and reduction
Oxidation and reduction in terms of electrons
4.4.2 Reaction of acids
Reactions of acids with metals
Neutralisation of acids and salt production
Soluble salts
The pH scale and neutralization
Titrations
Strong and weak acids
4.43 Electrolysis
Reactions: when metals react with other substances, they form cations (+ charge by losing e-).
Reactivity is related to a metal’s tendency to form cations.
Higher tendency, higher reactivity.
Reactivity series: lists the metals in order of reactivity.
Hydrogen and carbon are sometimes included despite being nonmetals.
A more reactive metal can displace a less reactive metal.
A more reactive metal can form a compound easier (can “fight” with a less reactive metal to form a compound).
Some metals, like gold, are very unreactive → found in their native form (alone) in nature.
Most metals are found in compounds; they must be extracted.
Using carbon for less reactive metals is a common method of extraction.
OILRIG: explains the loss and gain of electrons.
Oxidation is loss, reduction is gain
Charges should add up to the same number on both sides of the equation.
Whichever element becomes a cation has lost e- (opposite for anions, they gain).
Reaction: acid + metal → salt + hydrogen
Redox: one substance is oxidized while another is reduced (identify which using OILRIG).
Reactions:
Acid + alkali/base → salt + water
Alkali: soluble metal hydroxides.
Base: insoluble metal hydroxides and metal oxides.
Acid + metal carbonate → salt + water + carbon dioxide (acid is neutralized)
Salt Formation:
The type of salt formed depends on:
The acid in the reaction.
Positive ions in alkali/base/carbonate.
Soluble salt: forms when an acid reacts with a solid insoluble substance.
Add solid to acid until it no longer dissolves (achieved when some solid starts to sink to bottom- acid is neutralized).
Filter out excess solid, evaporate some water, leave the solution to evaporate on its own.
This is crystallization.
In aqueous solutions:
Acids produce H+ ions.
Alkalis produce OH- ions.
pH Scale: measures how acidic or basic/alkaline a solution is.
Ranges from 0-14.
if pH is 7 = neutral
if pH is <7 = acidic
if pH is >7 = alkaline/basic
*if an acid is stronger, its pH is lower (more acidic).
as pH decreases by 1, H+ concentration increases by a factor of 10.
Neutralization ionic reaction: H+(aq) + OH-(aq) → H2O(l)
Titrations: used to calculate and quantify the concentration of an unknown substance in a solution.
*know the process of creating a titration and calculating concentrations:
→ in-depth link for creating titration: Titration - Science Practicals: GCSE
→ in-depth link explaining titration calculations: 21.18: Titration Calculations - Chemistry LibreTexts
Strong acid: completely ionized in aqueous solution.
low pH
E.g hydrochloric acid
Weak acid: partially ionized in aqueous solution.
E.g ethanoic acid
*strong and weak refer to H+ concentration in solutions (don’t mix this up with concentrated and diluted solutions; they describe amount of solute in a substance/solution)
Electrolysis: a current is passed through a solution (or molten substance), breaking down the compound into its elements (forming charged electrolytes).
+ charged ions go to cathodes (- electrode), and - ions go to the anodes (+ electrode)
When an ionic compound goes through electrolysis, the metal will be produced at the cathode (as they become + ions due to losing e-).
This can also be used to extract metals.
This is usually done to very reactive metals in molten compounds (metals that can’t be extracted using carbon due to higher reactivity or metals that react with carbon).
Energy is added to melt the compounds.
Example: manufacturing process of aluminum using aluminum oxide, carbon, and cryolite.
Aqueous solutions are also electrolysed.
Water dissociates to H+ and OH- ions.
The most reactive ions want to stay in solution, and won’t be produced at the electrodes.
4.4.1 Reactivity of metals
Extraction of metals and reduction
Oxidation and reduction in terms of electrons
4.4.2 Reaction of acids
Reactions of acids with metals
Neutralisation of acids and salt production
Soluble salts
The pH scale and neutralization
Titrations
Strong and weak acids
4.43 Electrolysis
Reactions: when metals react with other substances, they form cations (+ charge by losing e-).
Reactivity is related to a metal’s tendency to form cations.
Higher tendency, higher reactivity.
Reactivity series: lists the metals in order of reactivity.
Hydrogen and carbon are sometimes included despite being nonmetals.
A more reactive metal can displace a less reactive metal.
A more reactive metal can form a compound easier (can “fight” with a less reactive metal to form a compound).
Some metals, like gold, are very unreactive → found in their native form (alone) in nature.
Most metals are found in compounds; they must be extracted.
Using carbon for less reactive metals is a common method of extraction.
OILRIG: explains the loss and gain of electrons.
Oxidation is loss, reduction is gain
Charges should add up to the same number on both sides of the equation.
Whichever element becomes a cation has lost e- (opposite for anions, they gain).
Reaction: acid + metal → salt + hydrogen
Redox: one substance is oxidized while another is reduced (identify which using OILRIG).
Reactions:
Acid + alkali/base → salt + water
Alkali: soluble metal hydroxides.
Base: insoluble metal hydroxides and metal oxides.
Acid + metal carbonate → salt + water + carbon dioxide (acid is neutralized)
Salt Formation:
The type of salt formed depends on:
The acid in the reaction.
Positive ions in alkali/base/carbonate.
Soluble salt: forms when an acid reacts with a solid insoluble substance.
Add solid to acid until it no longer dissolves (achieved when some solid starts to sink to bottom- acid is neutralized).
Filter out excess solid, evaporate some water, leave the solution to evaporate on its own.
This is crystallization.
In aqueous solutions:
Acids produce H+ ions.
Alkalis produce OH- ions.
pH Scale: measures how acidic or basic/alkaline a solution is.
Ranges from 0-14.
if pH is 7 = neutral
if pH is <7 = acidic
if pH is >7 = alkaline/basic
*if an acid is stronger, its pH is lower (more acidic).
as pH decreases by 1, H+ concentration increases by a factor of 10.
Neutralization ionic reaction: H+(aq) + OH-(aq) → H2O(l)
Titrations: used to calculate and quantify the concentration of an unknown substance in a solution.
*know the process of creating a titration and calculating concentrations:
→ in-depth link for creating titration: Titration - Science Practicals: GCSE
→ in-depth link explaining titration calculations: 21.18: Titration Calculations - Chemistry LibreTexts
Strong acid: completely ionized in aqueous solution.
low pH
E.g hydrochloric acid
Weak acid: partially ionized in aqueous solution.
E.g ethanoic acid
*strong and weak refer to H+ concentration in solutions (don’t mix this up with concentrated and diluted solutions; they describe amount of solute in a substance/solution)
Electrolysis: a current is passed through a solution (or molten substance), breaking down the compound into its elements (forming charged electrolytes).
+ charged ions go to cathodes (- electrode), and - ions go to the anodes (+ electrode)
When an ionic compound goes through electrolysis, the metal will be produced at the cathode (as they become + ions due to losing e-).
This can also be used to extract metals.
This is usually done to very reactive metals in molten compounds (metals that can’t be extracted using carbon due to higher reactivity or metals that react with carbon).
Energy is added to melt the compounds.
Example: manufacturing process of aluminum using aluminum oxide, carbon, and cryolite.
Aqueous solutions are also electrolysed.
Water dissociates to H+ and OH- ions.
The most reactive ions want to stay in solution, and won’t be produced at the electrodes.
