13.2 Acid-base reactions (ESBQY)

The reactivity in between an acid and also a base is well-known as a neutralisation reaction. Often when an acid and also base react a salt and water will certainly be formed. We will look at a few examples of acid-base reactions.

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In chemisattempt the word salt does not mean the white substance that you sprinkle on your food (this white substance is a salt, yet not the just salt). A salt (to chemists) is a product of an acid-base reaction and is comprised of the cation from the base and the anion from the acid.

Hydrochloric acid reacts via sodium hydroxide to form sodium chloride (a salt) and also water. Sodium chloride is consisted of of ( extNa^+) cations from the base (( extNaOH)) and ( extCl^-) anions from the acid (( extHCl)).

< extHCl (aq) + extNaOH (aq) ightarrow extH_2 extO (l) + extNaCl (aq)>

Hydrogen bromide reacts with potassium hydroxide to develop potassium bromide (a salt) and water. Potassium bromide is comprised of ( extK^+) cations from the base (( extKOH)) and also ( extBr^-) anions from the acid (( extHBr)).

< extHBr (aq) + extKOH (aq) ightarrow extH_2 extO (l) + extKBr (aq)>

Hydrochloric acid reacts with ammonia to develop ammonium chloride (a salt). Ammonium chloride is comprised of ( extNH_4^+) cations from the base (( extNH_3)) and ( extCl^-) anions from the acid (( extHCl)).

< extHCl (aq) + extNH_3 ext(aq) ightarrowhead extNH_4 extCl (aq)>

You have to alert that in the first two examples, the base consisted of ( extOH^-) ions, and also therefore the products were a salt and also water. ( extNaCl) (table salt) and also ( extKBr) are both salts. In the third example, ( extNH_3) likewise acts as a base, despite not having actually ( extOH^-) ions. A salt is still created as the just product, yet no water is produced.

It is essential to realise how beneficial these neutralisation reactions are. Below are some examples:

Domestic uses

Calcium oxide (( extCaO)) is a base (all steel oxides are bases) that is put on soil that is also acidic. Powdered limerock (( extCaCO_3)) deserve to likewise be used however its activity is a lot slower and also less reliable. These substances have the right to additionally be offered on a larger scale in farming and in rivers.

Limestone (white rock or calcium carbonate) is offered in pit latrines (or lengthy drops). The limerock is a base that helps to neutralise the acidic waste.

Biological uses

Acids in the stomach (e.g. hydrochloric acid) play a vital duty in helping to digest food. However before, as soon as a perboy has actually a stomach ulcer, or as soon as there is also much acid in the stomach, these acids deserve to reason a lot of pain. Antacids are taken to neutralise the acids so that they do not burn as much. Antacids are bases which neutralise the acid. Instances of antacids are aluminium hydroxide, magnesium hydroxide (“milk of magnesia”) and sodium bicarbonate (“bicarbonate of soda”). Antacids deserve to additionally be used to relieve heartburn.

Industrial uses

Basic calcium hydroxide (limewater) deserve to be supplied to absorb harmful acidic ( extSO_2) gas that is released from power stations and from the burning of fossil fuels.

Bee stings are acidic and have actually a pH in between ( ext5) and also ( ext5,5). They deserve to be soothed by utilizing substances such as bicarbonate of soda and also milk of magnesia. Both bases aid to neutralise the acidic bee sting and relieve some of the itchiness!

Acid-base reactions


To investigate acid-base reactions.

Apparatus and also materials

Volumetric flask conical flasks sodium hydroxide solution hydrochloric acid solution pipette indicator



Use the pipette to add ( ext20) ( extml) of the sodium hydroxide solution to a volumetric flask. Fill approximately the note through water and shake well.


Measure ( ext20) ( extml) of the sodium hydroxide solution into a conical flask. Add a few drops of indicator.

Slowly include ( ext10) ( extml) of hydrochloric acid. If tright here is a colour change soptimal. If not include one more ( ext5) ( extml). Continue adding ( ext5) ( extml) increments till you notification a colour readjust.


The solution changes colour after a collection amount of hydrochloric acid is included.

In the above experiment you supplied an indicator to view as soon as the acid had actually neutralised the base. Indicators are chemical compounds that change colour depending on whether they are in an acid or in a base.

A recommfinished experiment for informal assessment on discovering organic indications is included. Learners have the right to test a selection of colourful plants to watch what happens to each plant when blended via an acid or a base. The fundamental idea is for learners to extract the colour of the plant by boiling the plant matter and then draining the liquid. For substances such as the curry powder, learners deserve to disdeal with this in water and for the tea they deserve to brew a cup of tea and then remove the teabag prior to experimentation. The resulting liquid deserve to then be tested to watch if it is an indicator. An alternative to mixing the acid or base into the liquid is to soak strips of paper in the liquid and also then location a drop of the acid or base onto the paper. The experiment below also covers some various other substances such as baking powder, vanilla significance and also onions. Baking powder fizzes in acids however not in bases. Onions and vanilla essence lose their characteristic smell when in a basic solution.

It is important that learners carry out not place their faces or noses straight over or right into the beaker as soon as smelling the onions and vanilla significance. They must hold the beaker in one hand and usage the other hand to waft (i.e. wave their hand also ago and forth) the smell in the direction of their face.

Acids and bases are corrosive and also can reason significant burns so have to be taken on with care.



To determine which plants and foodstuffs have the right to act as indicators.

Apparatus and also materials

Possible indicators: Red cabbage, beetroot, berries (e.g. mulberries), curry powder, red grapes, onions, tea (rooibos or regular), baking powder, vanilla significance acids (e.g. vinegar, hydrochloric acid), bases (e.g. ammonia (in many household cleaners)) to test Beakers


Take a small amount of your first feasible indicator (perform not usage the onions, vanilla essence and also baking powder). Boil the substance up until the water has actually adjusted colour.

Filter the resulting solution into a beaker being mindful not to get any plant matter right into the beaker. (You have the right to likewise pour the water via a colander or sieve.)

Pour half the resulting coloured solution right into a second beaker.

Place one beaker onto an A4 sheet of paper labelled “acids”. Place the other beaker onto a sheet of paper labelled “bases”.

Repeat via all your other feasible signs (other than the onions, vanilla essence and also baking powder).

Into all the beakers on the acid sheet very closely pour ( ext5) ( extml) of acid. Record your observations.

Into all the beakers on the base sheet very closely pour ( ext5) ( extml) of base. Record your observations.

If you have even more than one acid or base then you will certainly need to repeat the over procedures to gain fresh indicator samples for your second acid or base. Or you deserve to usage less of the resulting coloured solution for each acid and base you desire to test.

Observe the smell of the onions and also vanilla essence. Place a small piece of onion right into a beaker. This is for trial and error through the acid. Pour ( ext5) ( extml) of acid. Wave your hand over the optimal of the beaker to blow the air in the direction of your nose. What perform you notice around the smell of the onions? Repeat via the vanilla significance.

Place a small piece of onion into a beaker. This is for trial and error via the base. Pour ( ext5) ( extml) of base. Wave your hand over the optimal of the beaker to blow the air in the direction of your nose. What execute you notice about the smell of the onions? Repeat through the vanilla essence.

Finally area a teaspoon of baking powder into a beaker. Carecompletely pour ( ext5) ( extml) of acid right into the beaker. Record your monitorings. Repeat making use of the base.

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Curry powder


Red grapes


Vanilla essence

Baking powder



Results with acid

Results through base

Red cabbage

You must note that some of the substances change colour in the visibility of either an acid or a base. The baking powder fizzes when it is in the acid solution, however no reactivity is provided as soon as it is in the base solution. Vanilla significance and also onions need to lose their characteristic smell as soon as in the base.