C5. Chemical Changes Flashcards
What is oxidation/reduction?
Oxidation - When a substance gains oxygen
Reduction - When a substance loses oxygen
What is the reactivity series of metals? What are the trends in reactivities of metals in reactions with acids/water?
The series shows the metals in order of their reactivity.
Metals above H₂ in the reactivity series react with acid to produce H₂. The more reactive the metal is, the quicker and more violent reaction with acid occurs.
Metals below H₂ don’t react with acids,
Not all metals above H₂ react with water - mostly Group I and II metals. Aluminium is the borderline case
What is a displacement reaction?
A reaction where a more reactive metal displaces a less reactive metal from a compound
How are unreactive metals found in Earth?
In their natural state
How can metals less reactive than carbon be extracted?
Reduction with carbon. Carbon displaces the metal in a metal oxide - gets oxidised to carbon oxides. Metal from the metal oxide gets reduced to the pure metal
How are metals more reactive than carbon extracted?
By electrolysis
How are oxidation and reduction defined in terms of electron transfer?
Oxidation - loss of electrons
Reduction - gain of electrons
What is the general equation for a reaction between metals and acids? What type of reaction is this?
Metal + acid –> Salt + hydrogen
Redox reaction, also a displacement reaction
Which metals in the reactivity series will react with acid?
Those above hydrogen
What is the general equation for a neutralisation reaction?
Base + acid –> salt +water
What is the general equation for the reaction between metal carbonate and acid?
Metal carbonate + acid –> salt + water + carbon dioxide
What is the general equation for the reaction between metal oxides and acids?
Metal oxide + acid –> a salt + water
What is a redox reaction?
A reaction where both oxidation and reduction occurs
Explain in terms of gain or loss of electrons which species has been oxidised and which species has been reduced when magnesium reacts with hydrochloric acid
Magnesium has lost electrons and thus has been oxidised (Mg to Mg²+)
The hydrogen in HCl has gained electrons and thus has been reduced (H+ to H₂)
How is a soluble salt formed?
a) React the excess acid with some insoluble chemical
b) Filter off the leftovers
c) Crystallise the product
What do acids and alkalis produce in aqueous solutions?
Acids produce hydrogen ions, alkalis produce hydroxide ions
What are bases, acids and alkalis?
Bases are compounds that neutralise acids, acids produce hydrogen ions in aqueous solutions, alkalis are soluble bases - produce hydroxide ions in aqueous solutions
What is the pH scale and what does a pH of 7 show?
The measure of acidity/alkalinity of a solution; neutral solution
State the general equation for a neutralisation reaction in a short, ionic form.
H+ + OH- —> H₂O
What is a strong acid and weak acid?
Strong acid is completely ionised in aqueous solution; weak acid is only partially ionised in aqueous solution
What happens to pH as concentration of H+ increases?
The pH decreases
What is a concentrated acid and what is a diluted acid? Is this the same as a strong and weak acid?
Concentrated acid has more moles of acid per unit volume than dilute (refers to solutions of low concentrations)
It is not the same - concentration is not the same thing as strength of an acid
Strength refers to whether the acid is completely ionised in water (strong) or only partially (weak)
As the pH is decreased by one unit, what change is seen in the hydrogen ion concentration?
Increases by a factor of 10
