4 Acids and redox Flashcards
What element do all acids contain? (1 mark)
Hydrogen
What does an acid release when dissolved in water? (1 mark)
H+ ions
What is a strong acid? (2 marks)
A strong acid releases all its hydrogen atoms into solution as H+ ions
and completely dissociates in aqueous solution.
What is a weak acid? (2 marks)
A weak acid only releases a very small proportion of its available hydrogen atoms into solution as H+ ions.
A weak acid only partially dissociates.
Define the term ‘base’. (1 mark)
A base is a substance which readily accepts H+ ions.
What is an alkali? (2 marks)
An alkali is a base that dissolves in water
releasing OH- ions into the solution.
What does an alkali release when dissolved in water? (1 mark)
OH- ions
Describe what happens when an acid is neutralised. (2 marks)
The H+ ions from acid react with OH- ions from base to form a salt and neutral water.
What is formed when an acid reacts with a metal hydroxide? (2 marks)
Water and a salt
What is formed when an acid reacts with a metal oxide? (2 marks)
Water and a salt
What are formed when an acid and alkali react? (2 marks)
Water and a salt
What are formed when an acid and metal carbonate react? (2 marks)
Water, carbon dioxide, and a salt
Explain the statement ‘Sulphuric acid is a strong acid, but this is true only for one of the two hydrogen atoms. (3 marks)
When sulphuric acid is mixed with water each H2SO4 molecule dissociates, releasing just one of its two hydrogen atoms as an H+ ion.
This means HSO4 - ions are formed, which behave as a weak acid.
Finish the sentence:
A burette reading is recorded to the nearest…. (1 mark)
Half division
What is a concordant result, in titration, and what are they used for? (2 marks)
Titres within 0.10cm3 of each other.
They are used to calculate the mean titre.
What is the oxidation number of an element? (1 mark)
0
Where is the sign placed for an oxidation number? (1 mark)
BEFORE the number
What is the oxidation number of hydrogen in metal hydroxides? (1 mark)
-1
e.g. NaH or CaH2
What is the oxidation number of oxygen in peroxides? (1 mark)
-1
e.g H2O2
What is the oxidation number of oxygen when bonded to fluorine? (1 mark)
+2
e.g. F2O
What is a redox reaction? (1 mark)
Redox reactions involve reduction and oxidation.
What is oxidation in terms of electrons? (1 mark)
The loss of electrons.
What is reduction, in terms of electrons? (1 mark)
The gain of electrons.
What is oxidation, in terms of oxygen? (1 mark)
Gain of oxygen.
What is reduction, in terms of oxygen? (1 mark)
Loss of oxygen.
What is oxidation, in terms of oxidation number? (1 mark)
Increase in oxidation number.
What is reduction, in terms of oxidation number? (1 mark)
Decrease in oxidation number.
What is the significance of oxidation number in equations? (1 mark)
The changes in oxidation number balance out in an equation.
