Acid-base & Redox Reactions (OCR A Level Chemistry A): Flashcards
Exam code: H432
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Define acid
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Cards in this collection (23)
Define acid
An acid is a substance that releases H+ ions (protons) when dissolved in water.
True or False?
A strong acid fully dissociates into ions in solution.
True.
A strong acid releases 100% of its H+ ions in solution. Dissociation is complete and irreversible.
Why does a weak acid form an equilibrium in solution?
A weak acid only partially dissociates, so both the undissociated acid and its ions are present at the same time. An equilibrium is established between them.
When a metal carbonate reacts with an acid, the products are a salt, .......... and ..........
When a metal carbonate reacts with an acid, the products are a salt, water and carbon dioxide.
What type of salt is produced when sulfuric acid reacts with a base?
Sulfuric acid produces a sulfate salt. For example, it reacts with copper carbonate to give copper sulfate.
True or False?
A strong base partially dissociates in solution to release OH- ions.
False.
A strong base fully dissociates in solution. All of the base releases OH- ions — partial dissociation is the behaviour of a weak base.
Define alkali
An alkali is a soluble base that releases hydroxide (OH-) ions when dissolved in water.
Define standard solution
A standard solution is a solution of accurately known concentration, used as a reference in titrations and volumetric analysis.
Why is a volumetric flask used when preparing a standard solution?
A volumetric flask allows the solution to be made up to a precise, fixed volume, minimising uncertainty in the final concentration.
True or False?
A burette has a precision of ±0.05 cm3.
True.
A burette is marked to 0.10 cm3 and, as an analogue instrument, its uncertainty is recorded to half the smallest marking: ±0.05 cm3.
Titration results are described as concordant if they are within .......... cm3 of each other.
Titration results are described as concordant if they are within 0.10 cm3 of each other.
What is the formula linking concentration, moles and volume?
Concentration (mol dm-3) = moles (mol) ÷ volume (dm3). To find moles, multiply concentration by volume, remembering to convert cm3 to dm3.
Complete these these steps for making a standard solution:
Weigh out the solute using a 3 d.p. balance
Dissolve in a small volume of .......... in a beaker
Transfer to a volumetric flask using a funnel
Rinse the beaker and add rinsings to the flask to avoid .......... loss
Make up to the .......... with distilled water and invert to mix
Weigh out the solute using a 3 d.p. balance
Dissolve in a small volume of distilled water in a beaker
Transfer to a volumetric flask using a funnel
Rinse the beaker and add rinsings to the flask to avoid solute loss
Make up to the mark with distilled water and invert to mix
True or False?
The rough titre is included in the average titre calculation.
False.
The rough titre is discarded because it is typically far beyond the end point and would make the average unreliable.
Define oxidation number
An oxidation number (or oxidation state) is the theoretical charge an atom would have if all bonding were completely ionic.
True or False?
Oxidation and reduction always occur together in a redox reaction.
True.
Every redox reaction involves simultaneous oxidation (increase in oxidation number) and reduction (decrease in oxidation number).
What happens to an oxidising agent during a redox reaction?
An oxidising agent accepts electrons, so it undergoes reduction — its oxidation number decreases.
Uncombined elements have an oxidation number of ..........
The oxidation number of a simple ion equals its ..........
In a neutral compound, the sum of oxidation numbers is ..........
Uncombined elements have an oxidation number of 0
The oxidation number of a simple ion equals its charge
In a neutral compound, the sum of oxidation numbers is 0
In a redox reaction, what is a reducing agent and what happens to it?
A reducing agent donates electrons and is itself oxidised — its oxidation number increases during the reaction.
True or False?
The oxidation number of oxygen is always −2 in all compounds.
False.
Oxygen is −2 in most compounds, but it is −1 in peroxides (e.g. H2O2) and +2 in F2O.
In the reaction Zn + 2HCl → ZnCl2 + H2, zinc's oxidation number changes from 0 to .......... and is therefore ..........
In the reaction Zn + 2HCl → ZnCl2 + H2, zinc's oxidation number changes from 0 to +2 and is therefore oxidised.
What are the default oxidation numbers of hydrogen and oxygen in most compounds?
Hydrogen is +1 in most compounds (exception: metal hydrides, e.g. NaH, where H = −1). Oxygen is −2 in most compounds (exception: peroxides, e.g. H2O2, where O = −1).
In the reaction Zn + 2HCl → ZnCl2 + H2, hydrogen's oxidation number changes from +1 to .......... and is therefore ..........
In the reaction Zn + 2HCl → ZnCl2 + H2, hydrogen's oxidation number changes from +1 to 0 and is therefore reduced.
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