8.4 Strong and Weak Acids and Bases

Strong and Weak Acids

[H⁺] is equal to [HCl] & [HNO₃], and equal to2 [H₂SO₄].

HCl --> H⁺ + Cl^-

HNO₃ --> H⁺ + NO₃^-

H₂SO₄ --> 2H⁺ + SO₄^2-

But weak Acids only partly dissociate.

CH₃COOH ⇌ H⁺ + CH₃COO^-

How do we know?

Water is covalent – there are almost no H⁺ + OH^- ions to carry charge.

1 moldm^-3 HCl produces [H⁺] = 1 moldm^-3 and a pH = log (1) = 0 {pH isn’t necessary 1-14}

1 moldm^-3 CH₃COOH produces [H⁺] = 4.2 x 10 ^-3 moldm^-3 which means that there are far fewer ions to carry charge.

Complete the sentences below

So, equimolar solutions of strong and weak monoprotic acids do not conduct equally well. Strong acids conduct better/worse because there is a higher/lower concentration of ions to carry charge.

If we applied the same voltage to both the current would be higher/lower in the weak acid.

In a 1 M solution of HCl the [H⁺] is much higher/lower than in a 1 M solution of Ethanoic acid. If we mix an equal volume of both acids with excess Magnesium powder both would react and give off bubbles of ______________ gas. But the ________________ acid would react more slowly because ________________ ________________________________________________________________________________________________________________________________.

As a consequence the Ethanoic Acid would have a faster/slower rate of reaction. We could follow the rate of reaction by collecting the gas in a ____________________________ and recording the volume every 5 seconds.

Or by placing the reaction vessel on an electronic balance and recording the mass every 5 seconds as it goes up/down

Both the Strong and the weak acid will make the same volume of Hydrogen because ____________________________________________________________________________________________________________ ____________________________________________________________________________________________________________

Both the Strong and the weak acid will make the same volume of Hydrogen because ____________________________________________________________________________________________________________

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All Acid-Alkali neutralisations have the same Ionic Equation:

H⁺_(aq) + OH^-_(aq) --> H₂O_(l)

So ΔH_{neutralisation} should be the same for all neutralisations.

However, when a weak acid is neutralised by a weak base ΔH_{neutralisation} is lower.

Suggest a reason why this should be the case (Hint: Bond breaking is endothermic)

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