1. Everyday examples of uses
of Acids, Alkalis
& Hazard Signs in the home,
school/college laboratory, industry, and in your body!
Examples of everyday acids
in the home or industry, hazard warning symbols (safety signs!), examples of the pH of common materials in aqueous solution
e.g. acids, alkalis, salts you may encounter from domestic products to the
school or college laboratory
Index of all my GCSE notes on acids, bases
GCSE Chemistry Revision
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Acids, alkalis and salts are different types of
chemicals with a huge variety of uses. Alkalis The chemistry of acids and bases–alkalis is
introduced by looking at common domestic examples in the home and not just in
industry or the chemical laboratory. Lime, antacids, lime, bee/wasp stings,
sodium bicarbonate, ammonia, sodium hydroxide, hydrochloric acid all get a
These revision notes on the use of acids, alkalis, pH
meters, pH paper and examples of the pH of many solutions and hazard signs
(hazard warning symbols) for acids and alkalis should prove useful for the new
AQA chemistry, Edexcel chemistry & OCR chemistry GCSE (9–1, 9-5 & 5-1) science
chemistry revision notes: basic school chemistry science GCSE chemistry, IGCSE chemistry, O level
& ~US grades 8, 9, 10 school science courses for ~14-16 year old science
students for national examinations in chemistry topics including acids
bases alkalis salts preparations reactions
a few examples of everyday acid–alkali chemistry
In this introductory page of 'everyday' acid, alkali and salt chemistry,
I have assumed that in your earlier school studies you have gained some
idea of what the terms pH, acid, alkali, salt and neutralisation mean.
You should know that acids and bases/alkalis react together in a
neutralisation reaction to form salts which occur in many domestic
products for the home and garden.
If you are not sure any term used in section 1. revise the basics from
section 2., which eventually
goes on a bit further theoretically in section 2c.
BUT some REMINDERS:
The pH scale is a measure of how acidic or alkaline a solution is.
A low pH is very acid, pH 7 is
neutral, a very high pH means very alkaline
An indicator is a dye molecule that changes colour depending on the
pH of the solution.
Universal indicator is a mix of indicators to produce a wide range of
colours to match a pH.
The diagram above illustrate the colours you can see with a typical
However its not as accurate as a specially calibrated instrument
called a pH meter - see picture at the end of the page.
but the terms used on this page like acid, alkali and pH
are explained in more theoretical detail in Part 2 ...
pH scale, indicators, ionic theory of acids, alkalis
(bases) & neutralisation
EXAMPLES of the 'everyday life' of acids, alkalis and
neutralisation to form salts
Theoretically the pH scale extends to <1 and >14 and there are solutions that
are so acid or so alkaline!
The pH scale is a measure of the relative acidity or alkalinity of an aqueous
Each pH unit is a factor of 10, but the lower the value, the more acidic the
Alkaline lime/quicklime (CaO, calcium oxide) or slaked lime (Ca(OH)2,
calcium hydroxide), are put on soil that is too acid for healthy plant growth,
they raise the pH by neutralising the acidity in the soil.
limestone (CaCO3, calcium carbonate) is slower and less
All three chemicals react with acids to neutralise them.
The pH scale is fully explained on the next page
pH scale, indicator
colours, ionic theory of acids, alkalis
(bases) & neutralisation
You can pre–test the
soil with pH paper and match the colour the paper turns with the pH
number it indicates.
These chemicals can be used on a larger scale in farming
and treating acidic rivers and lakes.
alkali ammonia NH3 is a component in some oven cleaners and will react with
Citric acid is found in citrus fruits and is used as a food and
drink flavouring, as is tartaric acid.
Table salt, used in preserving food and sprinkling over your fish
and chips as a flavouring etc. is the chemical sodium chloride NaCl.
HCl and phosphoric acid H3PO4 are components of
Salts are used to produce the colours in
fireworks e.g. sodium chloride a yellow flame, calcium chloride
makes a red flame and copper chloride can produce green and blue
Antacid indigestion tablets are mild
alkalis that react by neutralising excess stomach acid
which is the
'strong' hydrochloric acid which your delicate stomach lining and
upper gut can only take so much of.
The antacids must be weak bases i.e.
mild alkalis or harmless insoluble bases like calcium carbonate or
magnesium hydroxide which readily react with hydrochloric acid.
However, strong alkalis
are not to be recommended as a suitable medication for 'heartburn'
afflictions, since they can be just as irritating as strong
acids! See hazard warning signs further down the page and also "Investigation
of Indigestion Tablets".
Bicarbonate or (sodium hydrogencarbonate NaHCO3,
sodium bicarbonate, baking powder)
can be used with sour milk (acidic) for raising action in baking. The acidic
milk reacts with 'Bicarb' to form carbon dioxide gas giving the rising action.
You can easily demonstrate this by adding any common laboratory acid to baking
powder or any other carbonate!
Acidic bee stings
can be soothed,
i.e. neutralised by calamine lotion, which is a mildly alkaline
antiseptic and anti–itching agent based
zinc oxide. You can also use baking soda ('bicarb of soda' or
sodium hydrogen carbonate), another mild alkali. Hydrocortisone, an
anti-inflammatory agent helps too.
Wasp stings are supposed to be alkaline, but apparently not so! they are almost
neutral at pH 6.8–6.9 but are 'traditionally' treated with vinegar which is a weak
acid (and then perhaps you need the calamine too!).
I've come across references on the web to say that wasp stings are
not alkaline so 'English folklore' and mild–weak acid treatment has no real
It should be pointed out that sting venom is a complex mixture, including many
protein–enzymes, which, with other 'foreign' substances, might well trigger a response from the bodies
So, in all honesty, I'm not quite sure what the truth
is! However, what is known is that (i) bees and wasps have
glands that can secrete either acids or alkalis with other substances and (ii) ants sting
venom often contains methanoic acid ('formic acid') which can
have a pH
of 3 and is presumably 'soothed' by mild alkalis and just to confuse matters
more, (iii) many people claim the 'folklore' remedies
work! and maybe they do!
Ammonium salts, phosphate salts and
magnesium/potassium sulfate salts are used in fertilisers for the garden.
Soluble aspirin is made by neutralising the
acidic form of the medication with sodium hydroxide to make a soluble salt, or
its made in situ with a bicarbonate 'fizzing' mixture.
Acids and alkalis are useful in your body!
Your stomach produces hydrochloric acid to help in digestion of proteins.
Certain digestive enzymes only function properly in very acid conditions i.e. a
low pH <2. Pancreatic fluids are alkaline to suit the conditions required by
enzymes breaking down starches, fats and proteins.
The hydrochloric acid in your
stomach kills a large % of potentially harmful bacteria, minimising the risk of
food poisoning and irritation of the gut system.
However, as mentioned above, if
you produce too much acid you get indigestion and need to take an antacid
indigestion tablet to neutralise the excess. More body chemistry, preferably to
The strong alkali sodium hydroxide NaOH is
used bleaches and other cleaning
The equally strong alkali potassium hydroxide KOH
is used in alkaline batteries.
TOP OF PAGE
the chemical INDUSTRY
Alkalis like lime (calcium oxide, CaO) and limestone (calcium
carbonate, CaCO3) are used to reduce the acidity in soil,
the neutralisation reaction produces the optimum pH for crops to grow.
Sodium hydroxide NaOH, one of the most
commonly used alkalis, is used to neutralise aspirin making 'soluble
Aspirin is an organic acid and not very soluble in water,
its sodium salt is much more soluble and is absorbed faster by the
body for more effective treatment.
NH3 gas is
a weak alkali and neutralised by
sulfuric acid or nitric acid to form ammonium sulfate or ammonium
These are important agri–chemical fertilisers
to the soil for better plant growth.
some people prefer organic growing using good old muck and compost,
but it doesn't involve neutralisation, but it does involve my wife,
who is a member of the Soil Association! NPK fertilisers for
agriculture contain potassium, ammonium and phosphate salts.
harmful sulfur dioxide gas
(acidic, irritating and toxic SO2) in power station smoke
from burning fossil fuels, by absorbing it in alkaline calcium
hydroxide solution (limewater) to absorb it. Eventually harmless
calcium sulfate solution is formed.
Acids can be used to clean corroded
metal surfaces because of their reactivity to metals and metal
oxides to form soluble salts which can be washed away to leave a
cleaner metal surface.
Concentrated acid solutions are used to
remove limescale from the ceramic (unreactive) sides of toilets.
the build–up of a limestone like deposit in areas of hard water.
Alkalis are important chemicals in many industrial processes e.g.
Heating natural oils and fats with strong alkalis like sodium
hydroxide produces soaps.
Alkalis are used either directly, or to
make other chemicals that bind natural dyes to cloth and other
The alkali sodium carbonate is used in making glass.
the past alkalis have been obtained from burnt wood, burnt seaweed
and stale urine, but they are now may made on a huge bulk scale from
industrial processes e.g. sodium chloride is manufactured from the
electrolysis of brine (sodium chloride solution) and is then used to
make many other products.
Sodium carbonate is made from calcium
carbonate (limestone) and common salt (sodium chloride) by the
all of this is still pretty important chemistry even for the 21st century, with
strong links to agriculture, the environment and leading a stressful
Of course there
are 'downsides' to some of this 'acidic' chemistry:
Acid rain increases the rate of
corrosion of stonework (particularly limestone) and metal
Acid rain makes water too acid for
some aquatic organisms to live and this in turn affects food chains
e.g. salmon do not like water with a pH below 4.5!
Living on Venus could be hard going,
its atmosphere is mainly sulfuric acid,
mind you, you should be ok in
a plastic suit because plastics don't usually react with acids,
which is why, as well as being cheaper, plastics are replacing water
pipes, drain pipes and gutters etc.
HAZARD WARNING SYMBOLS you should know
hazard signs for irritant, harmful and corrosive are those most
appropriate when dealing with acids and alkalis
HAZARD WARNING SIGN
experiments, appropriate risk assessments should be done and hazcards
studied etc. This table illustrates the use of hazard warning signs
with common examples, and may NOT provide sufficient detail for specific
laboratory experiments and detailed safe procedures, concentration factors (e.g.
concentrated, 'doing labs', coursework write up from school/college
||Examples of what might be labelled/classified with this hazard
warning sign (definitions above)
Most acidic and alkaline solutions unless very dilute, VERY small
quantities of acidic gases like
chlorine, sulfur dioxide, nitrogen dioxide, very dilute bleaches. These
may not be that corrosive BUT they are irritating e.g. will cause irritation of the skin and
reddening and blistering.
Some acids e.g. nitric acid; acidic gases like chlorine,
sulfur dioxide, nitrogen dioxide; bleaches; heavy metal ions
e.g. of lead, barium; some salts e.g. silver nitrate, copper sulfate. They
are not quite as harmful as toxic chemicals but they can certainly make you
||Corrosive: Any substance like
concentrated acidic or alkaline solutions which will attack many materials
and destroy living tissue too! Also includes substances like bromine.
flammable: Most organic solvents like hexane, propanone (acetone), petrol and other
hydrocarbon fuels are easily ignited, easily catch fire.
Chlorine, sulfur dioxide, hydrogen cyanide can cause death if breathed in
with sufficient quantity, absorbed through the skin or ingested by
swallowing. Salts of hydrogen cyanide e.g. potassium cyanide are highly
toxic – you only have a short time to take an antidote mixture!
Chemicals that can act as oxidising agents e.g. chlorine gas/solution and oxygen gas/liquid, potassium manganate(VII), potassium chlorate (in some
weed killers). Many oxidising agents donate oxygen to materials that burn
and can be dangerously reactive. Many can cause combustion if mixed with an
oxidisable combustible material. They may cause materials to burn more
TNT, hydrogen, fireworks, peroxides
Radioisotopes giving off dangerous ionising radiation
||Harmful to the environment.
e.g. chemicals toxic to aquatic wildlife an in general
harmful to organisms and the environment e.g. toxic metals like mercury, old
pesticides like DDT.
pH examples of common acidic, alkaline and
neutral substances in aqueous solution
The pH scale
and indicators are explained in more detail in section 2.,
The diagram illustrates what you might see when
a universal indicator (mixture of several different colour changing
indicators) is added to a variety of solutions with a wide variation of pH
i.e. a wide range of acidity and alkalinity.
Basically a low pH 0-1 is very acid, pH 7 is
neutral (e.g. pure water), and a high pH 13-14 means very alkaline (~
means approximately in the table below).
An acid solution is defined as one with a pH of
less than 7, neutral solutions have a pH of 7 (or as near as make no
difference if the solutions has acidic or alkaline properties) and alkaline
solutions have a pH of over 7. The 'opposite' of an acid is a base, and a
soluble base is called an alkali.
The lower the pH the more acid the
The higher the pH the
more alkaline the solution.
It is important to understand two things about pH
and pH scale:
(i) pH is a measure of the hydrogen ion (H+)
concentration (see section 2.
Acidic solutions are formed when a
substance dissolves in water and forms hydrogen ions.
The lower the pH, the higher the
hydrogen ion concentration, that is more acid.
I know this seems confusing, but that's the way pH
scale has been defined.
(ii) Each pH unit change is equivalent to a 10x change in
concentration of the hydrogen ion (1 x 10).
For example changing the pH of a
solution from pH 3 to pH 4 makes it 10x less acidic.
Changing a solution's pH from 7 to 5 makes it 100x
more acidic (10 x 10).
sulfuric acid (car battery acid) pH 1
(ascorbic acid) pH ~3
very pure deionised H2O
hydroxide pH 13–14
acid (in the lab is same as your stomach!) pH 0–1
acetic/ethanoic acid (vinegar) pH ~3
chloride (salt water) ~pH 7
calcium hydroxide (limewater, slaked lime) pH 12
hydroxide pH 13–14
nitric acid pH 1
juices e.g. orange juice and lemon juice contain citric acid pH 2–3
sulfate (Epsom salts) pH ~6.5 – 7.0
sodium carbonate (washing soda) pH 11
cleaner if it
contains NaOH, pH can be >12, so take care!
Limescale remover, pH <1, so take care!
(glucose and other
sugars) pH 7
ammonia pH 11, in some domestic cleaning fluids
might also be over pH 12
pH 3 – 6
ethanol ('alcohol') pH 7
Caustic soda drain cleaner can be pH
13–14, based on sodium hydroxide
rain water naturally has a pH of pH ~5.6 due
to the dissolved weakly acidic gas carbon dioxide from the atmosphere ('carbonic
but it can fall to pH ~3.5 due to even more acidic sulfur dioxide gas from
fossil fuel burning.
See my local acid rain
some 'natural fluids' e.g.
blood ~7.2 – 7.4
~6.4 – 6.9
cows milk ~6.6
human milk 6.6 – 7.6
Sea water has a pH of ~7.5 – 8.5 and has many different salts
dissolved in it and bicarbonates causing the very slight alkalinity.
cider 2.9 – 3.3
Was sting, pH 6.8 – 6.9
sodium hydrogen carbonate ('bicarb', baking soda, bread soda) pH 8
Bee sting, pH 5.0 – 5.5
magnesium hydroxide ('milk of magnesia') pH 10 – 10.5
Pancreatic juice for your digestive
system can be as alkaline as pH
Washing–up liquid ~pH 8–9
|You can measure the pH
of a solution very accurately using a pH meter and a glass membrane pH
The pH meter is calibrated against
a standard buffer solution of accurately known pH
It is a much more
accurate method than universal indicator
GCSE/IGCSE Acids & Alkalis revision notes sub–index:
Index of all pH, Acids, Alkalis, Salts Notes 1.
Examples of everyday acids, alkalis, salts, pH of
solution, hazard warning signs : 2.
pH scale, indicators, ionic theory of acids–alkali neutralisation : 4.
Reactions of acids with
metals/oxides/hydroxides/carbonates, neutralisation reactions : 5.
Reactions of bases–alkalis
like ammonia & sodium hydroxide : 6. Four methods
of making salts : 7. Changes in pH in a
neutralisation, choice and use of indicators : 8. Important formulae
of compounds, salt solubility and water of crystallisation :
More on Acid–Base Theory and Weak and Strong Acids
Advanced Level Chemistry Students Acid–Base Revision
Notes – use index
Multiple choice revision quizzes and other worksheets
GCSE/IGCSE foundation–easier multiple choice quiz on pH, Indicators, Acids,
Bases, Neutralisation and Salts
GCSE/IGCSE higher–harder multiple choice quiz on pH, Indicators, Acids,
Bases, Neutralisation and Salts
GCSE/IGCSE Structured question worksheet on Acid
Reaction word equations and
equation answers and
GCSE/IGCSE word–fill worksheet on Acids,
Bases, Neutralisation and Salts
matching pair quiz on Acids, Bases, Salts and pH
Advanced Level Chemistry Students Acid–Base Revision
Notes – use index
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