6b. Making a soluble salt from an acid and an
insoluble base (can be an oxide, hydroxide, carbonate) or metal
Sub-index of salt preparation
methods
Method (a)
Making a salt by neutralising a soluble acid with a soluble base (alkali) -
neutralisation reaction
Method (b)
preparing a salt by reacting an acid with a metal or with an
insoluble base - oxide, hydroxide or carbonate (this page)
Method (c) Preparing an
insoluble salt by mixing solutions of two soluble compounds
Method (d) Making a
salt by directly combining its constituent elements
Index of all GCSE level (~US grades 8-10) notes on acids, bases
and salts
What next?
Associated Pages
Doc Brown's
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
6. METHODS of MAKING SALTS - salt
preparation procedures
Salt solubility affects the method you
choose to make a salt, the table below will help you decide on the method
A solubility guide
for salts and other compounds
Information required to decide on the method used to
prepare a salt |
salts and other compounds |
solubility? |
common salts of sodium, potassium and
ammonium ions |
usually soluble in water |
common sulfates (sulfates) |
usually quite soluble except for
calcium sulfate (slightly soluble), lead sulfate and barium sulfate
are both insoluble |
common chlorides (similar rule for
bromides and iodides) |
usually soluble except for
insoluble lead(II) chloride and silver chloride |
common nitrates |
all soluble |
common carbonates |
most metal carbonates are insoluble
apart from sodium & potassium carbonate. Ammonium carbonate is
also soluble |
common hydroxides |
most metal hydroxides are insoluble
apart from sodium, potassium and ammonium hydroxide |
One important point is to recognise
that one of the reactants is insoluble here, which is why you can't use a titration
procedure to work out how much of the acid is to be added to a given amount of
the solid. However, you can add the solid reactant to the acid until no more
reacts and dissolves and then filter off the excess solid leaving a solution of
the desired salt.
6b.
A 2nd
Method
of Making a Water Soluble Salt
6b. METHOD
(b)
Reacting
an acid with a metal or with an insoluble base to
give a soluble salt
e.g. an insoluble base such as a metal oxide, metal hydroxide or a metal carbonate, often of a Group 2 metal like
calcium, magnesium or a Transition Metal like nickel, copper or zinc. Copper
metal won't dissolve in acids, but its oxide and carbonate will. Using the same
procedure you can also start with a metal that has a low reactivity towards
water e.g. magnesium, zinc or iron.
Typical common insoluble bases used for
preparing soluble salts:
MgO magnesium oxide, MgCO3
magnesium carbonate, CaO Calcium oxide, CaCO3 calcium carbonate,
Ca(OH)2 calcium hydroxide, NiO nickel(II) oxide, ZnO zinc oxide, Zn(OH)2,
zinc hydroxide, ZnCO3 zinc carbonate, CuO copper(II) oxide, CuCO3
copper(II) carbonate, PbCO3 lead(II) carbonate (with nitric acid to
make lead(II) nitrate), FeCO3 iron(II) carbonate (to make iron(II)
salts), MnCO3 manganese(II) carbonate
Typical examples shown by the word and symbol
equations below include ...
copper(II) oxide +
sulfuric acid ==> copper(II) sulfate
+
water
CuO +
H2SO4 ==> CuSO4 +
H2O
CuO(s) +
H2SO4(aq) ==> CuSO4(aq) +
H2O(l)
magnesium hydroxide + sulfuric acid ==> magnesium sulfate
+
water
Mg(OH)2 +
H2SO4 ==> MgSO4 +
2H2O
Mg(OH)2(s) +
H2SO4(aq) ==> MgSO4(aq) +
2H2O(l)
magnesium hydroxide + hydrochloric acid
==>
magnesium chloride + water
Mg(OH)2(s) + 2HCl(aq)
==>
MgCl2(aq) + 2H2O(l)
Zinc carbonate + nitric acid ==> zinc nitrate +
water + carbon dioxide
ZnCO3 + 2HNO3
==> Zn(NO3)2 + H2O + CO2
ZnCO3(s) + 2HNO3(aq)
==> Zn(NO3)2(aq) + H2O(l)
+ CO2 (g)
zinc oxide + hydrochloric acid
==>
zinc chloride +
water
ZnO(s) + 2HCl(aq)
==>
ZnCl2(aq) +
H2O(l)
Similar for
many other Group 2 and Transition metal oxides e.g. Mg, Ca, Ba and Co, Ni,
Cu instead of Zn
zinc + sulfuric acid ==> zinc
sulfate + hydrogen
Zn + H2SO4
==> ZnSO4 + H2
Zn(s) + H2SO4(aq)
==> ZnSO4(aq) + H2(g)
calcium carbonate + hydrochloric acid
==>
calcium chloride + water + carbon dioxide
CaCO3(s) + 2HCl(aq)
==>
CaCl2(aq)+ H2O(l) + CO2(g)
Similar for
many other Group 2 and Transition metal carbonates e.g. Mg, Sr, Ba and Ni,
Co, Zn instead of Ca
-
Carbonates are frequently used
in this method of salt making, e.g. using copper carbonate to make copper
salts
-
copper(II)
carbonate + hydrochloric acid ==> Copper(II) chloride + water +
carbon dioxide
-
and with sulfuric acid
a blue solution of copper(II) sulfate is formed.
copper(II)
carbonate + sulfuric acid ==> Copper(II) sulfate + water +
carbon dioxide
copper(II)
carbonate + nitric acid ==> Copper(II) nitrate + water +
carbon dioxide
Similar equations for other
carbonates to give soluble salts
which can be crystallised from solution e.g.
-
calcium carbonate
CaCO3, to make two salts - calcium
chloride/nitrate (calcium sulfate is not very soluble)
-
iron(II) carbonate FeCO3,
to make three salts - iron(II) chloride/sulfate/nitrate
-
magnesium carbonate MgCO3,
to make three salts - magnesium chloride/sulfate/nitrate
-
manganese(II) carbonate MnCO3,
to make three salts - manganese(II) chloride/sulfate/nitrate
-
zinc carbonate ZnCO3,
to make three salts - zinc chloride/sulfate/nitrate
-
lead(II) carbonate PbCO3,
only nitric acid to make lead(II) nitrate, lead(II) chloride and
lead(II) sulfate are insoluble and must be prepared by method (c)
More examples of neutralization
equations are given in section 4.
METHOD
(b) Procedure for making a soluble salt from an insoluble base, carbonate
or metal
Don't forget to wear safety glasses or goggles when doing
this preparation.
(1) The required volume of acid is measured out into the
beaker with a measuring cylinder. The excess of insoluble metal, oxide,
hydroxide or carbonate is weighed out (*) and the solid added in small portions
to the acid in the beaker with stirring. Doing a weighing will minimise trial and error
especially if the reaction is slow, as long as you know how to do the
theoretical calculation and add on a little excess!
You need to be able to calculate the
quantities required.
(*) You can avoid doing a calculation and weighing of the
insoluble solid reactant by adding small quantities to the hot acid until no
more apparently dissolves.
(2) The mixture may be heated to speed up the
reaction. When no more of the solid dissolves it means ALL the acid is
neutralised and there should be a little excess solid.
You should see a
residue of the solid (oxide, hydroxide, carbonate) left at the bottom of the
beaker.
(3) The hot solution (with care!) is
filtered
to remove the excess solid metal/oxide/carbonate, into an evaporating dish.
On filtration, only a solution of the salt is left i.e. the liquid that passes
through the filter paper.
(4) You may need to carefully heat the solution to
evaporate some of the water.
This evaporation can be done safely with an
electric heater of a hot water bath.
Then hot concentrated solution is left to cool and crystallise.
After
crystallisation, you
collect and dry the crystals with a filter paper.
Extra guidance notes
(i)
Apparatus used: (1) balance, measuring cylinder, beaker and glass
stirring rod. (2) beaker/rod, bunsen burner,
tripod and gauze; (3)-(4) filter funnel and filter paper, evaporating
(crystallising) dish.
(ii)
A measuring cylinder is adequate for measuring the acid volume, you do not
need the accuracy of a pipette or burette required in method (a).
(iii) How to calculate amounts
required and % yield is dealt with in
 Chemical Calculations Part 14
Salt solubility affects the method you choose to
make a salt and so section 8. contains
tables of information-data on salt solubility which will help you decide on
the method to prepare a salt.
What next?
Associated Pages
Index of all my GCSE level (~US grades
810) notes on acids, bases
and salts
Email doc
brown comment? query?
HOME PAGE of Doc Brown's Science
UK KS3 Science Quizzes for
students aged ~11-14, ~US grades 6 to 8
Biology * Chemistry
* Physics notes for GCSE
level
students aged ~14-16, ~US grades 8 to 10
Advanced Level pre-university Chemistry
notes for students aged ~16-18 ~US grades 11 to 12
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 :
10.
More on Acid–Base Theory and Weak and Strong Acids
See also
Advanced Level Chemistry Students Acid-Base Revision
Notes - use index
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
symbol
equation questions
Word
equation answers and
symbol
equation answers)
GCSE/IGCSE word-fill worksheet on Acids,
Bases, Neutralisation and Salts
GCSE/IGCSE
matching pair quiz on Acids, Bases, Salts and pH
See also
Advanced Level Chemistry Students Acid-Base Revision
Notes - use index
Website content © Dr
Phil Brown 2000+. All copyrights reserved on Doc Brown's Chemistry revision notes, images,
quizzes, worksheets etc. Copying of website material is NOT
permitted. Exam revision summaries & references to science course specifications
are unofficial.
What next?
Associated Pages
|
|