Acids and Redox (Chapter 4) Flashcards by Rebecca Webb

What do all acids contain?

Hydrogen

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Define an acid

A substance that releases H+ ions in aqueous solution

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What happens when an acid is dissolved in water?

It releases H+ ions as protons into the solution

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Give an example equation of an acid forming

HCl(g) + aq (represents excess of water) = H+(aq) + Cl-(aq)

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What is a strong acid?

An acid that releases all of its hydrogen atoms into solution as H+ ions and completely dissociates in aqueous solution e.g. HCl

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What is a weak acid?

An acid that only releases a small proportion of its available hydrogen atoms into solution as H+ ions and therefore only partially dissociates in aqueous solution

e.g. CH3COOH(aq) <=> H+(aq) + CH3COO-(aq)
the equilibrium arrow shows that the forward reaction is incomplete

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Which proton is release as H+ in ethanoic acid?

The OH proton

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What are the common acids?

Hydrochloric acid, sulfuric acid, nitric acid and ethanoic acid

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What is the formula of sulfuric acid?

H2SO4

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What is the formula of nitric acid?

HNO3

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What is the formula of ethanoic acid?

CH3COOH

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What is the name of the salt for ethanoic acid?

Ethanoate

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What is the formula of ammonium ethanoate?

CH3COONH4

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What are the common alkalis?

NaOH, KOH and NH3

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What does a base do?

Neutralises an acid to form a salt

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Give some examples of bases

Metal oxides/hydroxides/carbonate, NH3

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What is an alkali?

A base that dissolves in water, releasing OH- ions into the solution

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Define an alkali

A substance that releases OH- ions in aqueous solution

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Give an example equation of an alkali forming

NaOH(s) + aq = Na+(aq) + OH-(aq)

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What is neutralisation?

The reaction of H+ and OH- to form H20

- The reaction of acids and bases to form salts

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What happens in the neutralisation of an acid?

H+(aq) ions react with a base to form a salt and neutral water
- the H+ ions from the acid are replaced by metal or ammonium ions from the base to form the salt

What happens when an acid is neutralised by a metal oxide/hydroxide (solids)?

Salt and water only are formed

What is the difference when acids are neutralised by alkalis?

The reactants are in solution

BUT same products (salt and water)

What is the ionic equation for neutralisation?

H+(aq) + OH-(aq) = H2O(l)

What happens when an acid is neutralised by a metal carbonate?

Salt, water AND CO2(g) are formed

What is a titration?

A technique used to accurately measure the volume of one solution that reacts exactly with another solution

What are titrations used for?

1) Finding the concentration of a solution 2) Identification of unknown chemicals 3) Finding the purity of a substance e.g. medicines and food

What is a standard solution?

A solution of known concentration

What is used to make up a standard solution?

A volumetric flask

What are the two pieces of apparatus used in a titration?

1) Pipette (normally 25cm3) | 2) Burette (normally 50cm3)

What two things do you have to remember when using a burette?

1) Burette readings are recorded to the nearest half division with the bottom of the meniscus on a mark or between 2 marks 2) Each reading is measure to the nearest ±0.5cm3, therefore the reading always has 2 d.p. with the last place as 0 or 5

What two things do you have to remember when doing a mean titre?

1) Use only your closest accurate titres - repeat until 2 agree within 0.10cm3 2) Mean titre to 1 d.p

What can the oxidation number be thought of as?

The number of electrons involved in bonding to a different element

What is the oxidation number for elements and why?

0, because in a pure element, any bonding is to atoms of the same element

What is the oxidation number of an ion?

The charge

What is the oxidation number of oxygen normally?

-2

What is the oxidation number of hydrogen normally?

What is the oxidation number of group 1/2 ions?

+1/+2

What is the oxidation number of the halogens normally?

-1

What is the oxidation number of hydrogen in metal hydrides?

-1 e.g. NaH and CaH2

What is the oxidation number of oxygen in peroxides?

-1 e.g. H2O2

What is the oxidation number of oxygen when bonded to fluorine?

+2 e.g. F2O

Sum of oxidation numbers =

Total charge of compound

When are roman numerals used in naming?

Used in the names of compounds of elements that form ions with different charges

What does the roman numeral show?

The oxidation state (number) of the element, without a sign

What does iron(II) represent?

Fe2+ with an oxidation number of +2

What does chlorate(I) represent?

ClO- where chlorine has an oxidation number of +1

What is a redox reaction?

A reaction that involves reduction and oxidation

What is oxidation?

- The loss of electrons - An increase in oxidation number - The addition of oxygen - The removal of hydrogen

What is reduction?

- The gain of electrons - A decrease in oxidation number - The addition of hydrogen - The removal of oxygen

Explain what has been oxidised and what has been reduced in this reaction: Zn(s) + 2HCl(aq) = ZnCl2(aq) + H2(g)

Zn has been oxidised because its oxidation number has increased by +2 and it has lost electrons H has been reduced because its oxidation number has decreased by 1 and it has gained electrons

How do you prepare a standard solution?

By dissolving an exact mass of the solute in a solvent and making up the solution to an exact volume