Reactions of Acids (AQA GCSE Chemistry)
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1/89What is the general equation for the reaction of a metal with an acid?
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What is the general equation for the reaction of a metal with an acid?
The general equation for the reaction between a metal and acid is:
metal + acid ⟶ salt + hydrogen
Which metals will react with dilute acids?
Metals above hydrogen in the reactivity series will react with dilute acids.
True or False?
Effervescence is produced when an acid reacts with a metal.
True.
Effervescence is produced when an acid reacts with a metal , due to the formation of hydrogen gas.
Why are metals such as sodium and potassium not commonly reacted with acids?
Metals such as sodium and potassium are not commonly reacted with acids because the reactions are dangerous / violent / explosive.
Name the salt formed when zinc reacts with sulfuric acid.
The salt formed when zinc reacts with sulfuric acid is zinc sulfate.
Write the word equation for the reaction of magnesium with hydrochloric acid.
The word equation for the reaction of magnesium with hydrochloric acid is:
magnesium + hydrochloric acid ⟶ magnesium chloride + hydrogen
Which metal and acid are required to form iron sulfate?
The metal and acid required to form iron sulfate are:
Iron,
Sulfuric acid.
In metal-acid reactions, which species is oxidised?
(Higher tier only)
In metal-acid reactions, the metal atoms are oxidised.
In metal-acid reactions, which species is reduced?
(Higher tier only)
In metal-acid reactions, the hydrogen ions are reduced.
True or False?
In metal-acid reactions, the metal gains electrons.
(Higher tier only)
False.
In metal-acid reactions, the metal loses electrons.
Write the half equation for the oxidation of zinc by hydrochloric acid.
(Higher tier only)
The half equation for the oxidation of zinc by hydrochloric acid:
Zn → Zn2+ + 2e-
True or False?
Redox reactions involve the transfer of electrons.
(Higher tier only)
True.
Redox reactions involve the transfer of electrons. Reduction involves gaining electrons, while oxidation involves losing electrons.
Why are metal-acid reactions considered redox reactions?
(Higher tier only)
Metal-acid reactions are considered redox reactions because both oxidation and reduction occur simultaneously.
Which species is oxidised in the following reaction?
Mg + 2H+⟶ Mg2+ + H2
(Higher tier only)
Magnesium is oxidised in the following reaction, because it has lost electrons.
Mg + 2H+⟶ Mg2+ + H2
Which species is reduced in the following reaction?
Fe + 2H+⟶ Fe2+ + H2
(Higher tier only)
Hydrogen ions are reduced in the following reaction, because they gain electrons.
Mg + 2H+⟶ Mg2+ + H2
What is a base?
A base is a chemical that neutralises acids.
What are the products of a neutralisation reaction between an acid and a base?
The products of a neutralisation reaction between an acid and a base are salt and water.
True or False?
All bases are soluble in water.
False.
Many bases are insoluble in water.
What is an alkali?
An alkali is a base that is soluble in water, forming an alkaline solution.
What three product are formed when an acid reacts with a metal carbonate?
The three products formed when an acid reacts with a metal carbonate are:
Salt,
Water,
Carbon dioxide.
What determines the identity of the salt produced in a neutralisation reaction?
The identity of the salt produced depends on:
The acid used,
The positive ions in the base.
True or False?
Hydrochloric acid produces sulfate salts.
False.
Hydrochloric acid produces chloride salts.
What type of salt does sulfuric acid produce?
Sulfuric acid produces sulfate salts.
What type of salt does nitric acid produce?
Nitric acid produces nitrate salts.
Write the symbol equation for the reaction of hydrochloric acid and copper(II) oxide.
The symbol equation for the reaction of hydrochloric acid and copper(II) oxide is:
2HCl + CuO → CuCl2 + H2O
Write the word equation for nitric acid reacting with magnesium oxide.
The word equation for nitric acid reacting with magnesium oxide is:
nitric acid + magnesium oxide → magnesium nitrate + water
True or False?
The balanced symbol equation for the reaction of sulfuric acid and potassium carbonate is:
2HCl + K2CO3 ⟶ 2KCl + H2O
False.
The balanced symbol equation for the reaction of sulfuric acid and potassium carbonate is:
2HCl + K2CO3 ⟶ 2KCl + H2O + CO2
How is a soluble salt made?
A soluble salt can be made by the reaction of an acid with a solid insoluble substance, such as :
metal.
metal oxide.
metal hydroxide.
metal carbonate.
Why is the insoluble base added in excess during the preparation of a soluble salt?
The insoluble base is added in excess to ensure that all of the acid has reacted.
What step is taken to remove the excess insoluble base after the reaction?
The excess insoluble base is removed by filtration.
What is left in the solution after the excess base is removed?
After removing the excess base, only the salt and water remain in the solution.
Write the balanced symbol equation for the preparation of copper(II) sulfate from copper(II) oxide.
The balanced symbol equation is:
CuO (s) + H2SO4 (aq) ⟶ CuSO4 (s) + H2O (l)
Define the term insoluble base.
An insoluble base is a base that does not dissolve in water.
How are crystals produced from a salt solution?
The solution is heated gently and then left to cool.
What does pH measure?
pH measures the concentration of hydrogen ions (H+) in a solution.
What is the pH range for acids?
Acids have pH values below 7.
What is the pH range for alkalis?
Alkalis have pH values above 7.
What pH value is considered neutral?
A pH value of 7 is considered neutral.
True or False?
A lower pH indicates a more acidic solution.
True.
A lower pH indicates a more acidic solution.
What is universal indicator?
Universal indicator is a wide range indicator made of a mixture of different plant indicators which operate across a broad pH range.
True or False?
Universal indicator gives an exact pH value.
False.
Universal indicator gives only an approximate value for pH.
What does an acid do in solution?
In solution, an acid ionises, producing protons (H+ ions), making the solution acidic.
What does a base (alkali) do in solution?
In solution, a base ionises, producing hydroxide ions (OH-) which can accept protons, making the solution alkaline.
True or False?
A pH probe measures pH more accurately than universal indicator.
True.
A pH probe measures pH more accurately than universal indicator.
What is the ionic equation for neutralisation?
The ionic equation for neutralisation is:
H+ (aq) + OH– (aq)⟶ H2O (l)
Define strong acid.
(Higher tier only)
A strong acid is an acid that completely dissociates (or ionises) in water, producing solutions of a very low pH.
Define weak acid.
(Higher tier only)
A weak acid is an acid that partially dissociates (or ionises) in water, producing pH values closer to the middle of the pH scale, while still being below 7.
True or False?
HCl is an example of a strong acid.
(Higher tier only)
True.
HCl is an example of a strong acid.
What is the equation for the dissociation of HCl in water?
(Higher tier only)
The equation for the dissociation of HCl in water is:
HCl (aq) → H+ (aq) + Cl- (aq)
True or False?
Weak acids form an equilibrium in water.
(Higher tier only)
True.
Weak acids form an equilibrium in water between molecules and their ions.
What is an example of a weak acid?
(Higher tier only)
Examples of weak acids are ethanoic, propanoic, citric and carbonic acids.
True or False?
Strong acids always have a higher pH than weak acids.
(Higher tier only)
False.
Strong acids always have a lower pH than weak acids of the same concentration.
What is the typical pH range for strong acids?
(Higher tier only)
The typical pH range for strong acids is 1-3.
What is the typical pH range for weak acids?
(Higher tier only)
The typical pH range for weak acids is 4-6.
True or False?
The terms "strong" and "concentrated" mean the same thing for acids.
(Higher tier only)
False.
"Strong" refers to the degree of dissociation, while "concentrated" refers to the amount of acid present in solution.
What is the difference between a strong and weak acid?
(Higher tier only)
A strong acid dissociates completely in water, while a weak acid only partially dissociates.
What does the ⇌ symbol indicate in the following dissociation of an acid?
CH3CH2COOH ⇌ H+ + CH3CH2COO–
(Higher tier only)
The ⇌ symbol indicates that the acid is weak, an equilibrium is established and the acid only partially dissociates.
True or False?
The higher the concentration of hydrogen ions in solution, the lower the pH.
(Higher tier only)
True.
The higher the concentration of hydrogen ions, the lower the pH.
If the pH increases by 1, how much does the concentration of hydrogen ions increase by?
(Higher tier only)
If the pH increases by 1, the concentration of hydrogen ions increases by a factor of 10.
Which acids of equal concentrations will have more hydrogen ions in solution, a weak acid or a strong acid?
(Higher tier only)
A strong acid will have more hydrogen ions in solution than a weak acid of equal concentration.
How many times greater is the concentration of hydrogen ions in a solution of pH 4 and pH 6?
(Higher tier only)
The concentration of hydrogen ions in a solution of pH 4 is 100 times (10 x 10) greater than a solution with a pH of 6.
If a hydrogen ion concentration in a solution of pH 5 increases by a factor 1000, what is the new pH?
(Higher tier only)
The new pH is 2.
If the hydrogen ion concentration increases by a factor of 10 by the pH decreases by 1.
So, increasing by a factor of 1000 will decrease the pH from 5 to 2.
What is a titration?
A titration is a method of analysing the concentration of solutions.
What is an acid-base titration used for?
An acid-base titration determines exactly how much alkali is needed to neutralise a quantity of acid, or vice versa.
What is the endpoint of a titration?
The endpoint is the point at which the indicator changes color, which means that neutralisation has happened.
True or False?
Wide range indicators like litmus are suitable for titrations.
False.
Wide range indicators like litmus are not suitable for titrations as they do not give a sharp enough color change at the endpoint.
What color does phenolphthalein turn in an alkaline solution?
Phenolphthalein turns pink in an alkaline solution.
What color does methyl orange turn in an acidic solution?
Methyl orange turns red in an acidic solution.
True or False?
Titrations can only be used for acid-base reactions.
False.
Titrations can also be used to prepare salts.
What is the purpose of using an indicator in a titration?
The purpose of using an indicator in a titration is to show the endpoint of the reaction.
What color is phenolphthalein in a neutral solution?
Phenolphthalein is colorless in a neutral solution.
What color does litmus paper turn in an alkaline solution?
Litmus paper turns blue in an alkaline solution.
State what is meant by concordant results.
Concordant results are results that are within 0.1 cm3 of each other.
What is the name of this piece of apparatus?
This piece of apparatus is a pipette.
Why is it important to repeat a titration?
Repeating a titration and achieving concordant results increases the accuracy of the measurement.
What is the purpose of swirling the flask during a titration?
Swirling the flask during a titration ensures thorough mixing of the solutions and helps to identify the endpoint more accurately.
Name the piece of equipment used to transfer a fixed volume of acid / alkali into a conical flask for a titration.
The piece of equipment used to transfer a fixed volume of acid / alkali into a conical flask for a titration is a volumetric pipette.
Why is a white tile placed underneath the conical flask during a titration?
A white tile placed underneath the conical flask during a titration because it allows the colour change to be observed more easily.
Name the piece of apparatus that measures a variable volume of acid / alkali during a titration.
The piece of apparatus that measures a variable volume of acid / alkali during a titration is a burette.
What is the name of this piece of apparatus?
This piece of apparatus is called a burette.
Define concentration, in the context of titrations.
(Higher tier only)
Concentration is the number of moles of solute per unit volume of solution, typically expressed in mol/dm3.
True or False?
The number of moles of acid always equals the number of moles of alkali in a titration.
(Higher tier only)
False.
The number of moles of acid and alkali depend on their reaction ratio, which is not always 1:1.
What units are typically used for volume in titration calculations?
(Higher tier only)
Volume is typically expressed in dm3 (cubic decimeters) in titration calculations.
How do you convert cm3 to dm3?
(Higher tier only)
To convert cm3 to dm3, divide by 1000.
True or False?
The concentration of a solution can be calculated if you know the number of moles of solute and volume of the solution.
(Higher tier only)
True.
The concentration of a solution can be calculated if you know the number of moles of solute and volume of the solution
What three pieces of information do you need to know when calculating the unknown concentration of an acid in an acid-base titration?
(Higher tier only)
The three pieces of information you need to know when calculating the unknown concentration of an acid in an acid-base titration are:
The volume (average titre) of the acid
The concentration of the base
The volume of the base.
Why is it important to consider the balanced equation in titration calculations?
(Higher tier only)
It's important to consider the balanced equation to determine the mole ratio between the acid and alkali.
Explain how many moles of HCl will be neutralised by 0.25 moles of NaOH.
HCl + NaOH → NaCl + H2O
(Higher tier only)
0.25 moles of HCl would be required as this reaction is a 1:1 ratio.
Explain how many moles of NaOH will be neutralised by 0.10 moles of H2SO4.
H2SO4 + 2NaOH → Na2SO4 + 2H2O
(Higher tier only)
0.20 moles of NaOH would be required as this reaction is a 2:1 ratio.