1.1.3 - Acids

Specification

Context and exemplification - Assessable learning outcomes

Acids and bases

Candidates should be able to:

(a) explain that an acid releases H+ ions in aqueous solution;

(b) state the formulae of the common acids: hydrochloric, sulfuric and nitric acids;

(c) state that common bases are metal oxides, metal hydroxides and ammonia;

(d) state that an alkali is a soluble base that releases OH- ions in aqueous solution;

(e) state the formulae of the common alkalis: sodium hydroxide, potassium hydroxide and aqueous ammonia; Salts

(f) explain that a salt is produced when the H+ ion of an acid is replaced by a metal ion or NH4 +;

(g) describe the reactions of an acid with carbonates, bases and alkalis, to form a salt;

(h) explain that a base readily accepts H+ ions from an acid: eg OH- forming H2O; NH3 forming NH4 +;

(i) explain the terms anhydrous, hydrated and water of crystallisation;

(j) calculate the formula of a hydrated salt from given percentage composition, mass composition or experimental data;

(k) perform acid-base titrations, and carry out structured titrations.

Acids and Bases

Explain that an acid releases H+ ions in aqueous solution

When acids are added to water, H+ ions are released into the solution. An acid is therefore a proton donor.

State the formulae of the common acids: hydrochloric, sulfuric and nitric acids

State that common bases are metal oxides, metal hydroxides and ammonia;

Common Metal Oxides: MgO and CuO

Common Metal Hydroxides: NaOH and Mg(OH)2

Ammonia – NH3

Amines – CH3NH2

Bases are proton acceptors and they neutralise acids.

State that an alkali is a soluble base that releases OH– ions in aqueous solution;

OH- ions are added to neutralise H+ ions, hence why bases neutralise acids.

State the formulae of the common alkalis: sodium hydroxide, potassium hydroxide and aqueous ammonia;

Sodium Hydroxide: NaOH

Potassium Hydroxide: KOH

Ammonia: NH3

Alkali’s are special bases that dissolve in water forming aqueous hydroxide ions (OH-)

e.g NaOH(s) + aq ----> Na+(aq) + OHHydroxideions from alkalis neutralise the protons from acids, forming water:

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


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Salts

Explain that a salt is produced when the H+ ion of an acid is replaced by a metal ion or NH4+;

Describe the reactions of an acid with carbonates, bases and alkalis, to form a salt;

Carbonates:

Acid + Carbonate ----> Salt + Carbon Dioxide + Water

Bases:

Acid + Base ----> Salt + Water

Alkalis

Acid + Alkali ----> Salt + Water

Ammonium Salts

Acid + Aqueous Ammonia ----> Ammonium Salt

NH3 + HNO3 ----> NH4NO3

Explain that a base readily accepts H+ ions from an acid:

eg OH– forming H2O; NH3 forming NH4+

Explain the terms anhydrous, hydrated and water of crystallisation;

Calculate the formula of a hydrated salt from given percentage composition, mass composition or experimental data;

1. Mass of hydrated – Mass of anhydrous = Mass of H20

2. Calculate number of moles of anhydrous substance

3. Calculate number of moles of water

4. Look at the molar ratio and divide by the smallest number of find the formula of the hydrated salt.


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