Acids and Alkalis
 Forming Acids
 Acids are formed from soluble non metal
oxides.
 They have a ph range between 1 and 7
 They turn pH paper of universal indicator
red/orange/yellow
Forming Alkalis
 Alkalis are formed from soluble metal
oxides.
 They have a pH range between 8 and 14
 They turn universal indicator and pH paper
Dark green/blue/purple
Examples of Acids and Alkalis
Acids
Hydrochloric Acid
Nitric Acid
Vinegar
Orange Juice
Sulphuric Acid
Carbonic Acid
Alkalis
Sodium Hydroxide
Toothpaste
Ammonia Solution
Calcium hydroxide
Potassium hydroxide
Bicarbonate of soda
Neutral Substances
 A neutral substance is neither acid nor alkali.
 They have a pH =7
 They turn universal indicator and pH paper
green.
Example – Water, Tea, Alcohol!
Acid Rain
 Acid rain is formed when acidic gases dissolve in
rain water.
 The main gas responsible is Sulphur dioxide!
 Oxides of Nitrogen can also contribute to the
problem.
 Acid rain damages the environment:
 Eats away buildings, kills plants and fish, corrodes
iron structures.
Preventing Acid Rain!
 Remove Sulphur from fuels before you burn
them.
 Reduce the amount of fossil Fuels you burn.
Dissociation of Water
 Water exists mainly as molecules – however it
sometimes splits into 2 ions – Hydrogen and
Hydroxide.
 H2O(l) <—–> H+ (aq) + OH- (aq)
 Water will conduct electricity – slightly because it
contains these ions.
 Water is neutral because it contains equal numbers
of each ion.
Conductivity
 Acids and Alkalis can conduct electricity
because they contain ions.
 Acids = H+ ion
 Alkalis = OH- ion
 The stronger the acid or alkali is – the more
ions it contains – the greater the
conductivity!
Diluting!
 When we add water to an acid or alkali– we
dilute it – reduce the concentration of the
ions!
 Acids – the concentration oh H+ ions gets
less – the pH will increase – moving towards
pH7
 Alkalis – the concentration of OH- will get
less – the pH will move down -towards pH 7
Electrolysis of Acids
 Acids will split up when you pass an electric
current through them.
 This is because they contain ions – Hydrogen ions.
 When we electrolyse Sulphuric Acid the following
happens:
 Bubbles of Hydrogen gas appear at the negative
electrode.
 The H+ ions move to the – electrode – they gain
electrons to form H2 gas
 2H+ (aq) + 2 e —> H2 (g)
Metal Hydroxides
 We can find out if a compound is soluble
using p5 in the data book.
 Trends
 Metal hydroxides in Group 1 and 2 are
soluble. E.g NaOH, KOH, Ca( OH )2
 All other metal hydroxides are insoluble.
e.g. Cu(OH)2, Zn(OH)2
Formula Mass
 This is the total mass of a compound.
 It takes into consideration the number and mass of
each element in a compound.
 Steps
 Correct Formula – Use valency rules!
 Write down numbers of each elements in
compound.
 Add in mass of element – use data book.
 Add up total mass.
Formula Mass – example!
 Work out the formula mass of Calcium hydroxide.
1. Formula – Ca 2+ OHCross over – Ca (OH)2
2. Numbers of each element
(1 x Ca) + (2 x O) + ( 2 x H)
3. Add in mass
( 1 x 40) + ( 2 x 16) + ( 2 x 1)
4. Add total mass
40 + 32 + 2 = 74 amu.
The Mole! – Gram Formula
Mass
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The mole is basically the formula mass in grams.
The steps are required.
Example – Calculate the mass of 1 Mole of Water
Symbol – H2O
Numbers of elements – ( 2 x H) + ( 1 x O)
Add in Mass - (2x1) + (1x 16)
Total Mass – (2x1) + 16 = 18 g
2 moles of water would be- 2 x18g = 32g
More Calculations!
n
C
V
n = Number of Moles
C = Concentration (mol/l)
V = Volume (l)
n=CxV
C = n/V
V = n/C
Examples
 1) Calculate – The number of moles if you
have a solution of with 2 mol/l HCl in
100cm3 of water.
 n = CxV
2 x 100/1000
2 x 0.1
= 0.2 moles
More!
 2) Calculate the volume of water required to
make a 2 mol/l solution of NaOH using 3
moles of the alkali.
 V = n/C
=3/2
= 1.5 litres
Even More!
 Calculate the concentration of solution made
when 2 mol/l of acid dissolves in 50 cm3 of
water.
 C = n/V
= 2/(50/1000)
= 2/ 0.05
= 40 mol/l