13.2 Acid-base reactions (ESBQY)

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

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In chemistry words salt walk not median the white substance the you sprinkle on her food (this white problem is a salt, yet not the only salt). A salt (to chemists) is a product of one acid-base reaction and also is made up of the cation indigenous the base and also the anion indigenous the acid.

Hydrochloric acid reacts with sodium hydroxide to form sodium chloride (a salt) and also water. Sodium chloride is consisted of of ( extNa^+) cations indigenous the basic (( extNaOH)) and also ( extCl^-) anions native the mountain (( extHCl)).

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

Hydrogen bromide reacts with potassium hydroxide to kind potassium bromide (a salt) and water. Potassium bromide is comprised of ( extK^+) cations indigenous 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 v ammonia to kind ammonium chloride (a salt). Ammonium chloride is made up of ( extNH_4^+) cations indigenous the base (( extNH_3)) and ( extCl^-) anions from the acid (( extHCl)).

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

You should notice that in the first two examples, the base included ( extOH^-) ions, and therefore the assets were a salt and water. ( extNaCl) (table salt) and also ( extKBr) room both salts. In the 3rd example, ( extNH_3) likewise acts together a base, regardless of not having ( extOH^-) ions. A salt is still developed as the only product, however no water is produced.

It is important to realise how valuable these neutralisation reaction are. Listed below are some examples:

Domestic uses

Calcium oxide (( extCaO)) is a basic (all steel oxides room bases) that is placed on soil the is as well acidic. Powdered limestone (( extCaCO_3)) can additionally be used yet its action is much slower and also less effective. This substances can also be provided on a larger scale in farming and also in rivers.

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

Biological uses

Acids in the stomach (e.g. Hydrochloric acid) play an important role in helping to digest food. However, as soon as a person has a stomach ulcer, or as soon as there is too much acid in the stomach, these acids can cause a the majority of pain. Antacids space taken come neutralise the mountain so that they don"t burn as much. Antacids space bases i beg your pardon neutralise the acid. Instances of antacids space aluminium hydroxide, magnesium hydroxide (“milk of magnesia”) and sodium bicarbonate (“bicarbonate that soda”). Antacids can also be offered to relieve heartburn.

Industrial uses

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

Bee stings space acidic and have a pH between ( ext5) and also ( ext5,5). They deserve to be soothed by utilizing substances such together bicarbonate of soda and milk of magnesia. Both bases assist to neutralise the acidic punishment sting and also relieve few of the itchiness!

Acid-base reactions


To inspection acid-base reactions.

Apparatus and materials

Volumetric flask conical flasks salt hydroxide equipment hydrochloric acid solution pipette indicator



Use the pipette to include ( ext20) ( extml) of the salt hydroxide solution to a volumetric flask. Fill approximately the note with water and also shake well.


Measure ( ext20) ( extml) the the salt hydroxide solution right into a conical flask. Include a couple of drops the indicator.

Slowly add ( ext10) ( extml) of hydrochloric acid. If there is a colour adjust stop. If not include another ( ext5) ( extml). Continue including ( ext5) ( extml) increments till you notice a color change.


The solution transforms colour ~ a set amount that hydrochloric acid is added.

In the above experiment you used an indicator to see once the acid had neutralised the base. Indicators are chemical compounds that change colour relying on whether they space in an acid or in a base.

A recommended experiment because that informal assessment on discovering natural indicators is included. Learners deserve to test a variety of colourful tree to see what happens to every plant when combined with an acid or a base. The simple idea is because that learners to extract the colour of the tree by boiling the tree matter and also then draining the liquid. Because that substances such as the curry powder, learners can dissolve this in water and for the tea they have the right to brew a cup the tea and then eliminate the teabag prior to testing. The result liquid deserve to then be experiment to see if the is one indicator. An different to mix the acid or base into the liquid is to soak strips of document in the liquid and also then place a autumn of the mountain or base onto the paper. The experiment below additionally covers some various other substances such together baking powder, vanilla essence and also onions. Baking powder fizzes in acids however not in bases. Onions and vanilla essence lose your characteristic smell when in a simple solution.

It is crucial that learners execute not place their deals with or noses straight over or into the beaker as soon as smelling the onions and vanilla essence. Lock must hold the maker in one hand and use the various other hand to waft (i.e. Tide their hand back and forth) the smell in the direction of their face.

Acids and also bases room corrosive and also can reason serious burns so have to be tackled with care.



To identify which plants and foods deserve to act together indicators.

Apparatus and also materials

feasible 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 numerous household cleaners)) to check Beakers


Take a little amount the your very first possible indicator (do not usage the onions, vanilla essence and baking powder). Cook the problem up till the water has readjusted colour.

Filter the result solution into a manufacturer being cautious not to get any plant matter right into the beaker. (You can also pour the water v a colander or sieve.)

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

Place one beaker ~ above an A4 paper of record labelled “acids”. Place the various other beaker ~ above a paper of document labelled “bases”.

Repeat v all her other possible indicators (except the onions, vanilla essence and also baking powder).

Into every the beakers ~ above the acid sheet carefully pour ( ext5) ( extml) of acid. Document your observations.

Into every the beakers ~ above the basic sheet carefully pour ( ext5) ( extml) of base. Record your observations.

If friend have an ext than one acid or base climate you will have to repeat the over steps to obtain fresh indicator samples because that your 2nd acid or base. Or you have the right to use much less of the result coloured solution for each acid and base you want to test.

Observe the odor of the onions and also vanilla essence. Place a little piece of onion right into a beaker. This is for testing with the acid. Pour ( ext5) ( extml) that acid. Tide your hand end the height of the beaker to blow the air towards your nose. What execute you notification about the odor of the onions? Repeat through the vanilla essence.

Place a small piece that onion right into a beaker. This is for trial and error with the base. To water ( ext5) ( extml) of base. Wave your hand over the peak of the maker to blow the air in the direction of your nose. What carry out you notification about the smell of the onions? Repeat through the vanilla essence.

Finally location a tespoon of baking powder right into a beaker. Closely pour ( ext5) ( extml) the acid right into the beaker. Record your observations. Repeat using the base.

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Curry powder


Red grapes


Vanilla essence

Baking powder



Results v acid

Results with base

Red cabbage

You have to note that several of the substances adjust colour in the presence of either an acid or a base. The baking flour fizzes once it is in the acid solution, yet no reaction is detailed when the is in the basic solution. Vanilla essence and onions should lose their characteristic smell when in the base.