Chemistry Reference
In-Depth Information
The number of moles of sulfuric acid which will react
with 4.03 × 10
−3
moles of sodium hydroxide
= 4.03 × 10
−3
×
1
Questions
1
24.2 cm
3
of a solution containing 0.20 mol dm
−3
of hydrochloric acid just neutralised 25.0 cm
3
of a
potassium hydroxide solution. What is the concentration
of this potassium hydroxide solution?
2
22.4 cm
3
of a solution containing 0.10 mol dm
−3
of
sulfuric acid just neutralised 25.0 cm
3
of a sodium
hydroxide solution. What is the concentration of this
sodium hydroxide solution?
2
= 2.015 × 10
−3
This is the number of moles of sulfuric acid present
in 25 cm
3
of the solution, so the concentration of the
sulfuric acid
= 2.015 × 10
−3
×
1000
25
= 0.081 mol dm
−3
Checklist
After studying Chapter 8 you should know and understand the
following terms.
•
Acid
A substance which dissolves in water, producing
H
+
(
aq
) ions as the only positive ions. An acid is a hydrogen
ion (H
+
) donor.
•
Acid salt
A substance formed when only some of the
replaceable hydrogen of an acid is replaced by metal ions or
the ammonium ion (NH
4
+
).
•
Alkali
A soluble base which produces OH
−
(
aq
) ions in
water.
•
Base
A substance which neutralises an acid, producing a
salt and water as the only products. A base is a hydrogen
ion (H
+
) accepter.
•
Double decomposition
The process by which an
insoluble salt is prepared from solutions of two suitable
soluble salts.
•
Effl orescence
The process during which a substance loses
water of crystallisation to the atmosphere.
•
Hygroscopic
The ability to absorb water vapour from the
atmosphere without forming solutions or changing state,
for example, concentrated sulfuric acid.
•
Indicator
A substance used to show whether a substance
is acidic or alkaline (basic), for example phenolphthalein.
•
Ionic equation
The simplifi ed equation of a reaction
which we can write if the chemicals involved are ionic
substances.
•
Neutralisation
The process in which the acidity or
alkalinity of a substance is destroyed. Destroying acidity
means removing H
+
(
aq
) by reaction with a base, carbonate
or metal. Destroying alkalinity means removing the OH
−
(
aq
)
by reaction with an acid.
H
+
(
aq
) + OH
−
(
aq
)
→
H
2
O(
l
)
•
Normal salt
A substance formed when all the replaceable
hydrogen of an acid is completely replaced by metal ions or
the ammonium ion (NH
4
+
).
•
pH scale
A scale running from 0 to 14, used for
expressing the acidity or alkalinity of a solution.
•
Salt hydrates
Salts containing water of crystallisation.
•
Solubility
The solubility of a solute in a solvent at a given
temperature is the number of grams of that solute which
can dissolve in 100 g of solvent to produce a saturated
solution at that temperature.
•
Strong acid
An acid which produces a high concentration
of H
+
(
aq
) ions in water solution, for example hydrochloric
acid.
•
Strong alkali
An acid which produces a high
concentration of OH
−
(
aq
) ions in water solution, for example
sodium hydroxide.
•
Testing for a carbonate
If effervescence occurs when
an acid is added to the suspected carbonate and the gas
produced tests positively for carbon dioxide, the substance
is a carbonate.
•
Testing for a chloride
If a white precipitate is produced
when dilute nitric acid and silver nitrate solution are added
to the suspected chloride, the solution contains a chloride.
•
Testing for a sulfate
If a white precipitate is produced
when dilute hydrochloric acid and barium chloride solution
are added to the suspected sulfate, the solution contains a
sulfate.
•
Titration
A method of volumetric analysis in which a
volume of one reagent (for example an acid) is added to a
known volume of another reagent (for example an alkali)
slowly from a burette until an end-point is reached. If an
acid and alkali are used, then an indicator is used to show
that the end-point has been reached.
•
Water of crystallisation
Water incorporated into the
structure of substances as they crystallise, for example in
copper(
ii
) sulfate pentahydrate (CuSO
4
.5H
2
O).
•
Weak acid
An acid which produces a low concentration
of H
+
(
aq
) in water solution, for example ethanoic acid. It is
only partially ionised.
•
Weak alkali
An acid which produces a low concentration
of OH
−
(
aq
) in water solution, for example ammonia solution.
It is only partially ionised.
