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Acids and BasesAcids and Bases1 2 3 4 5 6 7 8 9 10 11 12 13 14

Hydrochloric acid Citric acid Water

An acid is a “proton donor”:

A base is a “proton acceptor”:

HCl H Cl

+ -

H

ONa

H

ONa

-+

Sodium hydroxide

Ammonia

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Common acids and alkalisCommon acids and alkalis

Acids Alkalis

Hydrochloric acid, HCl

Sodium hydroxide, NaOH

Nitric acid, HNO3

Sulphuric acid, H2SO4

Potassium hydroxide, KOH

Magnesium hydroxide, Mg(OH)2

Calcium hydroxide, Ca(OH)2

20/04/23Arrhenius vs Lowry and Arrhenius vs Lowry and BronstedBronsted

Arrhenius, 1859-1927

Lowry, 1874-1936

I said that all acids release hydrogen ions and all alkalis form hydroxide ions

when dissolved in water.

Bronsted and I said that acids are “proton

donors” and bases are “proton acceptors”.

Bronsted and Lowry’s work was more accepted because of three things:

1) Arrhenius’ work depended on the existence of subatomic particles like protons, which hadn’t yet been discovered.

2) Arrhenius’ work couldn’t explain the behaviour of acids and bases in solvents other than water

3) Lowry and Bronsted worked independently but still agreed with each other

HNO3 - nitric acid

HCl- hydrochloric acid

H2SO4 - sulphuric acid

Acids donate protons

Acids and Bases

Sulphuric acid can donate two proton and so we say it is diprotic

HNO3(aq) H+(aq) + NO3

-(aq)

Metal oxides and metal hydroxides. Ammonia and organic compounds called Amines (e.g. CH3NH2) are also bases

Acids and BasesBases accept protons

MgO – magnesium oxide

NaOH- sodium hydroxide

NH3 - ammonia

Alkalis are soluble bases that release hydroxide ions into water

LiOH - lithium hydroxideMg(OH)2 - magnesium hydroxide

Alkalis

7

Biological Acid & BasesBiological Acid & Bases

These include - • Fatty acids• Amino acids• Nucleic acids

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Amino AcidsAmino Acids

• Building blocks of proteins• Carboxylic acid group• Amino group• Side group R gives unique characteristics

R = side chain

H

H2N—C—COOH

R

Acid

Base

These molecules have both acid and

base properties. We say they

are amphoteric.

A small amount of solid magnesium oxide, MgO, was reacted with excess dilute hydrochloric acid.

(a)Write a balanced equation for this reaction [1]

(b) Describe what would be seen as the reaction occurs

solid disappears/dissolves/colourless solution forms

MgO(s) + 2HCl(aq) MgCl2(aq) + H2O(l)

[1]

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