Acid base reactions

Acids and bases comprise two important groups of compounds, commonly defined respectively as donors or acceptors of protons. They are easily detected by their interaction with pH indicators, which change colour according to the presence of an acid or a base.

According to the Brönsted definition, acidic substances are donors of hydrogen ions and in aqueous solutions they form oxonium ions.

HCl + H2O → Cl– + H+ + H2O → H3O+ + Cl–.

Bases react to give hydroxide ions in aqueous solution either by simple solution, in the case of alkali metal hydroxides.

Another definition of acids and bases was given by Lewis who defined an acid as a substance that can accept a lone pair of electrons and a base as a substance which donates a lone pair of electrons.

The acidity or alkalinity of solutions is measured by the pH scale that is pH= – log10[H3O+].

Some organic substances undergo reversible changes with acids or bases and change colour as they do so. For this.

• Litmus paper — 8884.02
• Beaker 100 ml — 1118.20
• Glass rod — 1444.10
• Dropping pipette — 1441.50+5448.00
• Test tubes — 1473.60
• Test tube rack — 1680.06
• Dissecting set — 8267.15
• Tripod stand — 5533.10
• Spirit burner — 5514.10
• Iron stand — 5404.52
• Wire gauze — 5534.25

• Distilled water
• Hydrochloric acid — R:34-37 S:26-45
• Sodium hydroxide — R:35 S:26-37/39-45
• Sodium chloride
• Ammonia — R:34-50 S:26-36/37/39-45-61
• Magnesium oxide
• Magnesium ribbon
• Acetic acid
• Vinegar
• Fresh lemon juice
• Red cabbage juice

• This experiment must be carried out in a fume cupboard or outdoors.
• Do not leave the bottles of hydrochloric acid and ammonia unstoppered.

• Record your observations of what happens.
• Record your observations and compare the results with those obtained using the indicator paper.
• Compare the results of all of these tests.