(1) When a substance dissolves in water it forms an aqueous solution which may be acidic,
or neutral. Water itself is
. An
can be used to show how acidic or alkaline a solution is by the way the
changes. The
scale is used to show numerically how acidic or alkaline a solution is. If the pH =
the solution is neutral, if the pH is over 7 it is
and if it is less than 7 it is
.
(2)
Q2 Compounds of alkali metals called salts can be made by reacting solutions of their hydroxides which are alkaline with acids. In these neutralisation reactions:
acid + alkaline hydroxide solution ==> a neutral
solution +
step A A known volume of acid is measured out with a measuring cylinder or more accurately with a pipette and suction bulb and universal indicator is added and turns
.
step B The alkali is added with a measuring cylinder, or more accurately with a
.
step C The alkali is added until the indicator turns
. The volume required for neutralisation is noted. If too much alkali is added the indicator turns
!
step D The procedure can now be
without the contaminating indicator. The solution is then
to reduce the amount of water.
step E The hot concentrated solution can be left to cool until the salt
from solution.
(3) The particular salt produced in any reaction between an acid and an alkali depends on the acid used and the metal in the alkali. Neutralising hydrochloric acid produces a
, nitric acid produces a
and neutralising sulphuric acid makes a
. Ammonia also dissolves in water to produce an
solution. This can be neutralised with acids to produce
salts. In the salt preparation an indicator can be used to show when acidic and alkaline solutions have been completely
to produce a neutral
solution.
(4)
Q4 Salts of transition metals, as with some other metals, can be made by reacting their
, hydroxides or carbonates with acids. Transition metal oxides and hydroxides do not
in water and are called insoluble
.
step A To produce a solution of a soluble transition metal salt, the metal oxide (or hydroxide or carbonate) is added to an acid until no more will react.
step B The excess metal oxide (or hydroxide) can then be
off. The fact that no more
tells you all the acid has been
.
step C The clear
solution is then warmed to
water until the salt
from
solution.