4.2 Reactions of acids
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What is oxidation / reduction?
Oxidation - When a substance gains oxygen Reduction - When a substance loses oxygen
How are oxidation and reduction defined in terms of electron transfer ? (Higher)
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? (Higher)
A reaction where both oxidation and reduction occurs
Explain in terms of gain or loss of electrons which element has been oxidised and which element has been reduced when magnesium reacts with hydrochloric acid. (Higher)
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?
● React the excess acid with some insoluble chemical (e.g. metal oxide) ● Filter off the leftovers ● 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. A pH of 7 is a neutral solution.
State the general equation for a neutralisation reaction in a short, ionic form.
OH− + H+→ H2O
What is a strong acid? What is a weak acid? (Higher)
Strong acids are completely ionised in an aqueous solution. Weak acids are only partially ionised in an aqueous solution.
What happens to pH as the concentration of H+ increases? (Higher)
The pH decreases
What is a concentrated acid and what is a dilute acid? Is this the same as a strong and weak acid? (Higher)
● Concentrated acid has more moles of acid per unit volume than dilute (dilute refers to solutions of low concentrations) ● It is not the same - concentration is not the same thing as the 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? (Higher)
Increases by a factor of 10
Name the following salts: LiNO3, K2CO3, MgBr2, BaSO4
● Lithium nitrate ● Potassium carbonate ● Magnesium bromide ● Barium sulfate