Acids and bases

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Acids have a pH of less than seven, bases have a pH of more than seven. When bases are dissolved
in water they are known as alkalis.
Hydrogen ions make a solution acidic ­ acids are corrosive
Hydroxide ions make a solution alkaline.
Equal numbers of hydroxide and hydrogen ions create a neutral solution. ( water)
Indicators
The pH scale is the measure of how many hydrogen ions are present in a solution. Lots of
hydrogen ions means strong acid, few hydrogen ions mean weak acid/alkali. Universal indicator is
a combination of dyes which can be dropped into a solution to find the pH. However the colour
you see and how acidic/alkali you think it is depends on your perception of colour.
Using litmus paper; an acid will go red, an alkali will go blue.
Reacting a strong acid + strong alkali We can use any indicator
Reacting a strong acid and a weak alkali We use Methyl Orange
Reacting a weak acid and strong alkali We use Phenolphthalein
Acid + Base ---> Salt and water. This is an example of a neutralisation reaction.
It can also be represented as:
Acid + Metal oxide ---> Water + Salt
Acid + Metal hydroxide ---> Water + salt [Metal oxide/hydroxide are also bases.]
When metals react with carbonates such as calcium carbonate they form a salt, water and carbon
dioxide. The co2 can be detected by bubbling the gas produced through lime water and seeing if it
turns cloudy.
Acids react with metals:
When an acid react with a metal it produces a salt and hydrogen. The hydrogen comes from the
acid e.g. hydrochloric acid contains hydrogen ions. When a metal and acid react, if the metal is
more reactive than hydrogen it can displace this hydrogen forming a metal salt + hydrogen.

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E.g. 2HCL + Mg ----> MgCl2 + H2
Acid + Metal -----> Metal salt + Hydrogen
The more reactive the metal, the faster the reaction will happen ­ very reactive metals react
explosively.
The speed of the reaction can be told by the rate a which the hydrogen bubbles are produced.
We can test to ensure it is definitely hydrogen present by the burning split test ­ if we hear a
squeaky pop then hydrogen is present.…read more

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An acid reacts with a base to form water (neutral solution) and a salt
h+ + OH- -----> H20 This is an example of a neutralisation.
Real life example of neutralisation:
1) Indigestion is caused by too much hydrochloric acid in the stomach. Indigestion tablets
contain bases such as magnesium oxide which neutralises the excess acid.
2) Fields with acidic soils can be neutralised with the use of calcium hydroxide (which is
sometimes called lime).…read more

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Ammonia can be neutralised with acid to form ammonium salts. Ammonia dissolves in
water to form an alkaline solution. This solution can be neutralised by the addition of an
acid to form ammonium salts e.g. Ammonia (solution) + Hydrochloric acid ---> Ammonium
chloride
or Ammonia + nitric acid ---> ammonium nitrate
NH3 + HNO3 ----> NH4NO3 (Ammonium nitrate)
Ammonium salts are useful as fertilisers.
This is different from typical neutralisation reactions as no water is produced.…read more

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Won't react with copper on its own as it is lower than hydrogen in the reactivity series. )
1) Heat up acid using a Bunsen burner until it is boiling in order to provide the particles with
more kinetic energy to increase the chances of successful collisions and increase the rate
of reaction.
2) Add the base (copper oxide) in excess. This is to ensure that the acid is completely
neutralised.…read more

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The excess base will sink to the bottom of the flask when all of the acid is neutralised. We then
filter the mixture to get rid of any excess base this will collect in the filter funnel
(carbonates/hydroxides.) Then evaporate off the water from the liquid by heating and you should
be left with pure, dry salt. (Go to BBC bite size.)
Remember is you use a metal carbonate carbon dioxide gas is given off also.…read more

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These protons become surrounded by water molecules to keep them in solution ­ we call it a
hydrated proton.
He defined an alkali as a substance which dissolves in water and dissociates to form hydroxide ions.
An alkali is a base which dissolves in water, and produces OH- ions (hydroxide ions).
His theory wasn't immediately accepted as he also suggested that molecules ionise/dissociate in
water which many scientists did not believe was possible as charged sub-atomic particles had not
been discovered yet.…read more

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The more concentrated an acid the
faster the reaction will occur.
Whereas the strength of an acid depends on how much is ionises/dissociates in water.
Strong and weak acids ­ more acidic takes longer to react/test using indicator
A strong acid is one that completely ionises in water so all of the compound dissociates
into ions.
E.g. hydrochloric acid, sulphuric acid, and nitric acid are al strong acids as there ions completely
dissociate in water. This means that in water e.g.…read more

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Titrations are used e.g. in medicine to find out exactly how much acid is needed to
neutralise a certain quantity of alkali or how much alkali is needed to neutralise a certain
quantity of acid. You need to know the exact amount as you can't'/don't want to add in
excess need the exact amount.…read more

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Need to know the indicators needed
Reacting a strong acid + strong alkali We can use any indicator
Reacting a strong acid and a weak alkali We use Methyl Orange
Reacting a weak acid and strong alkali We use Phenolphthalein
Equation
m1 x v1 = m2 x v2
1cm3 = 1/1000 = 0.…read more

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