Acids and Redox - exam practice
Acids and Redox
Question 1 of 7
Ammonium sulfate, (NH4)2SO4, is a salt formed from the neutralisation of ammonia by sulfuric acid.
Write a balanced equation for the formation of ammonium sulfate from ammonia and sulfuric acid. State symbols are not required.
Explain why ammonium sulfate is an example of a salt.
How is ammonia acting as a base in this neutralisation?
A student wants to determine the number of moles of ammonia in a 400 cm3 solution using a titration. They add 25.0 cm3 of the ammonia solution to a conical flask and titrate with 0.100 mol dm-3 H2SO4. The titre recorded was 31.75 cm3 of H2SO4.
Calculate the number of moles of ammonia in the 400 cm3 solution, giving your answer to 3 significant figures.
Ammonia can be used to produce hydrazine, N2H4, as shown in the reaction below.
2NH3 + NaClO ➔ N2H4 + NaCl + H2O
Use oxidation numbers to show that this is a redox reaction.
Ethanoic acid is a weak acid found in vinegar.
What is meant by the term weak acid?
The equation for the reaction between ethanoic acid and magnesium is shown below.
Mg(s) + 2CH3COOH(aq) ➔ (CH3COO)2Mg(aq) + H2(g)
Deduce, using oxidation states, which element has been oxidised and which element has been reduced.
A student uses a titration to determine the concentration of ethanoic acid in a sample of vinegar.
The student adds 25.0 cm3 of the vinegar to a volumetric flask and makes the solution up to 250 cm3 before transferring to a burette. They then add 25.0 cm3 of 5.00 x 10-2 mol dm-3 Ba(OH)2(aq) to a conical flask and titrate this with the vinegar solution, recording a mean titre of 24.17 cm3.
The equation for the reaction is shown below.
2CH3COOH(aq) + Ba(OH)2(aq) ➔ (CH3COO)2Ba(aq) + 2H2O(l)
Name the piece of apparatus used to measure 25.0 cm3 of Ba(OH)2(aq).
State what the burette should be rinsed with to improve the accuracy of the titration.
Calculate the concentration of CH3COOH in the vinegar, giving your answer to 3 significant figures.
Iodine can be used on a small scale to purify water. When iodine reacts with water, the following equilibrium is set up.
I2 + H2O ⇌ HI + HIO
Using oxidation numbers, explain why this equilibrium is an example of disproportionation.
Chlorine is also used to purify water but on a much larger scale. Chlorine can be manufactured by the reaction below.
MnO2(s) + 4HCl(aq) ➔ MnCl2(aq) + 2H2O(l) + Cl2(g)
Use oxidation numbersto show which substance has been oxidised and which has been reduced.
Nitrite ions, NO2−, react with chlorate (V) ions, ClO3−, to produce chlorine as shown in the reaction below.
2ClO3− + 5NO2− + 2H+ ➔ Cl2 + 5NO3− + H2O
In a titration experiment, 25.0 cm3 of sodium nitrite solution was completely reacted with 26.79 cm3 of 0.0200 mol dm-3 potassium chlorate(V) solution.
Calculate the concentration, in g dm-3, of sodium nitrite to 1 decimal place.
Chlorine is an important chemical and has a number of applications including sterilising water and extracting bromine from seawater. Chlorine can be formed by the oxidation of chloride ions.
In terms of electrons, what is meant by the term oxidation?
Write a half equation to show the oxidation of chloride ions to chlorine.
In the extraction of bromine from seawater, chlorine acts as an oxidising agent.
What is meant by the term oxidising agent?
Chlorine can also oxidise water to form oxygen.
Write an equation for this reaction and give the oxidation state of chlorine in the chlorine-containing product that is formed.
The processes of oxidation and reduction can be defined in terms of the transfer of electrons.
Define the term reduction in terms of electrons
The following reaction between copper and nitric acid can be used to produce NO.
3Cu + 8H+ + 2NO3− ➔ 3Cu2+ + 4H2O + 2NO
If the nitric acid is concentrated and warm, then NO2 can be produced instead of NO.
Give the oxidation states of nitrogen in NO3−, NO and NO2.
The half equation for the formation of NO2 from NO3− is:
NO3− + 2H+ + e− ➔ NO2 + H2O
State whether oxidation or reduction is occurring.
The half equation for the formation of NO from NO3−is:
NO3− + 4H+ + 3e− ➔ NO + 2H2O
State whether oxidation or reduction is occurring.
This question is about redox reactions.
State the meaning of the term redox as applied to a reaction.
Salts can be prepared in redox reactions of metals with acids. What is meant by a salt?
The aluminium sulfate salt, Al2(SO4)3, can be prepared by reacting aluminium with sulfuric acid.
Write the equation for reaction of aluminium and sulfuric acid.
Use oxidation numbers to show which element has been oxidised and which element has been reduced in part c).
MnO2 is an oxidising agent that can be used to oxidise iodide ions to iodine.
2I− + MnO2 + 4H+ ➔ Mn2+ + 2H2O + I2
Give the oxidation state changes of Mn and I and show that this is a redox reaction.
The percentage purity of a 0.850 g sample of impure iodine can be determined using a titration. The iodine is dissolved in potassium iodide solution and titrated with sodium thiosulfate according to the reaction below.
2S2O32− + I2 ➔ 2I− + S4O82−
The titration requires 28.85 cm3 of 0.200 mol dm−3 sodium thiosulfate.
Calculate the percentage purity of the sample of iodine, giving your answer to 3 significant figures.