Acid base reactions
To demonstrate the chief properties of acids and bases, and to introduce the concept of acids and bases and some indicators.
Cosa imparano gli studenti
La scienza alla base di questo esperimento
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.
Attrezzatura utilizzata
- Litmus paper — 8884.02
- Beaker 100 ml — 1118.20
- Glass rod — 1444.10
- Pipetta a goccia — 1441,50+5448,00
- Provette — 1473,60
- Portaprovette — 1680.06
- Dissecting set — 8267.15
- Tripod stand — 5533.10
- Bruciatore ad alcool — 5514.10
- Iron stand — 5404.52
- Wire gauze — 5534.25
Sostanze chimiche e reagenti
- Acqua distillata
- Hydrochloric acid — R:34-37 S:26-45
- Sodium hydroxide — R:35 S:26-37/39-45
- Cloruro di sodio
- Ammonia — R:34-50 S:26-36/37/39-45-61
- Magnesium oxide
- Magnesium ribbon
- Acetic acid
- Vinegar
- Fresh lemon juice
- Red cabbage juice
Note sulla sicurezza
- This experiment must be carried out in a fume cupboard or outdoors.
- Do not leave the bottles of hydrochloric acid and ammonia unstoppered.
Domande per gli studenti
- 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.
Cosa aspettarsi
<p>The litmus paper changes its colour in the following way: Hydrochloric acid: Red.</p><p>Sodium chloride: doesn’t change colour = NEUTRAL Ammonia solution: Blue.</p><p>Magnesium Oxide: Blue Acetic acid: Red Vinegar: Red.</p><p>Mg + 2 H+ → Mg2+ + H2.</p><p>Red cabbage juice is a natural pH indicator. It contains chemicals called anthocyanins, which are pigments that react in a different way to acids and bases.</p><p>Chemical substances that change colour in solutions of different pH values are contained in many flowers, fruits, and vegetables.</p><p>The pH values and colours of red cabbage extract.</p>
Smaltimento
Dispose of solutions into the liquid wastes container.
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