Chemical changes Flashcards
(35 cards)
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 reaction with acids/water?
The series shows the metals in order of their reactivity.
Metals above H₂ in 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 reacts with water. It is mostly group 1 and 2 metals that react. 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 - carbon 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
It is a redox reaction and 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 → salt + water
What is a redox reaction?
A reaction where both oxidation and reduction occurs.
Explain in terms of gain or loss of electron which species has been oxidised and which species has been reduced when magnesium reacts with hydrochloric acid
Magnesium has lost electrons and this 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?
1) React the acid with an excess of an insoluble base (such as metal oxide).
2) Filter off the leftovers.
3) 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 - produces hydroxide ions in aqueous solutions.
What is the pH scale and what does a pH of 7 show?
The pH scale is a 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
H⁺ + OH⁻ → H₂O
What is a strong acid? What is a weak acid?
Strong acids are completely ionised in aqueous solutions.
Weak acids are only partially ionised in aqueous solutions.
What happens to pH as concentration of H⁺ increases?
pH goes to more acidic scale.
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 volumes than dilute.
It is not the same - concentration is not the same thing as strength of 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 changes is seen in hydrogen ion concentration?
Increases by a factor of 10.
Name the following salts: LiNO₃, K₂CO₃, MgBr₂, BaSO₄
- Lithium nitrate.
- Potassium carbonate.
- Magnesium bromide.
- Barium sulphate.
