5.2 Salts
Not just a flavour!
Can be formed several ways
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•
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Acid – Base Neutralization
Oxides and carbonates reacting
with acid
Metal reacting with acid
Salts have many uses
•
Table Salt:
NaCl
Aluminum Sulfate:
Al2(SO4)3
Making batteries, explosives,
fertilizers, multivitamin and mineral
tablets, blood and urine, tree sap
Magnesium
acetate:
Mg(CH3COO)2
Salts - Neutralization
•
•
•
•
•
•
A Salt results when an acid reacts with a
base. Both are neutralized.
The H+ and OH- ions combine to form water.
The non-metallic ions of the acid and the
metal ions of the base form the salt.
Acid + Base ----> Salt + Water
HCl + NaOH ----> NaCl + H2O
H2SO4 + Ca(OH)2 ----> CaSO4 + H2O
Metal and non-metal oxides
Chemically combined with oxygen.
Metal oxide: a metal combined with oxygen
•
•
Solution becomes basic when dissolved in water
Na2O(s) + H2O (l)
2NaOH (aq)
Non-metal oxide: a non-metal combined with
oxygen
•
•
Solution becomes acidic when dissolved in water
SO3 (g) + H2O (l)
H2SO4 (aq)
Acids and Metals
The most reactive metals appear on the extreme left of the periodic table
•
•
When metals react with acids, they usually
release hydrogen gas
2HCl (aq) + Mg (s)
MgCl2(aq) + H2 (g)
online metals in acid demo
Acids and Carbonates
Carbonate is a combination of carbon and oxygen
•
Carbonate (CO3) is trapped in rocks
When carbonate rocks react with acids, the
carbonates help neutralize the acid
Liming is a process that people do to help
neutralize acidic lakes.
Liming adds calcium carbonate (CaCO3) to
the lake. Very expensive.
Carbonates reacting with acid release CO2
•
H2SO4 + CaCO3
•
•
•
•
CaSO4 + H2O + CO2
The Naked Egg
The chemistry of removing an egg shell
Eggshells are made up of calcium carbonate
•
CaCO3
•
CH3COOH
•
5% acetic acid 95% water
Vinegar is also called acetic acid (5% solution)
The chemical reaction is:
2CH3COOH + CaCO3
•
Ca(CH3COO)2 + H2O + CO2
The eggshell has been removed leaving the thin membrane called a
semi-permeable membrane which water can pass through.
•
What were the bubbles on the surface of the egg?
•
Think about the impact of acid rain on shells in nature!
The Naked Egg
Bubbles of CO2
Osmosis: water traveling through a membrane from a
high concentration to a low concentration.
5.2 Salts
• Salts are ionic compounds formed when acids and bases react.
 Salts are also produced when oxides or carbonates react with acids or when metals
react with acids.
• Table salt, NaCl, is found in sea water, salt lakes or rock deposits.
 Salt was once very valuable as a commodity.
 Iodine is now added to salt to minimize goiter (a disease of the thyroid).
• NaCl is only one kind of salt.
 A salt is made up of a positive ion
from a base and a negative ion from
an acid.
 Salts are found in many things:
 In batteries, explosives and fertilizers
 In multivitamins
 In many living cells
Salt crystals in Death Valley
See pages 234 - 235
(c) McGraw Hill Ryerson 2007
Acid-Base Neutralization, and
Metal Oxides and Non-Metal Oxides
• Neutralization reactions occur when an acid and a base react to produce a salt
and water.
 HCl(aq) + NaOH(aq)  NaCl(s) + H2O(l)
acid
base
salt
water
• Metal oxides react with water to form bases.
 Na2O(s) + H2O(l)  2NaOH(aq)
• Non-metal oxides react with water to form acids
 SO2(g) + H2O(l)  H2SO3(aq)
 Non-metal oxides are formed from the burning of fossil fuels.
 Acid added to water in the atmosphere = acid precipitation.
The effects of acid
rain on a forest
See pages 236 - 237
(c) McGraw Hill Ryerson 2007
Acids and Metals, and
Acids and Carbonates
• Acids and Metals
 The most reactive metals, at the bottom of groups 1 and 2 on the periodic
table, react vigorously with water and acids.
 All other metals are less reactive than those in groups 1 and 2.
 When metals do react with acids, H2 gas is usually released.
 2HCl(aq) + Mg(s)  MgCl2(s) + H2(g)
• Acids and Carbonates
 Carbonates neutralize acids, protecting locations with natural carbonate
supplies from acid precipitation.
 H2SO4(aq) + CaCO3(s)  CaSO4(s) + H2O(l) + CO2(g)
sulphuric
acid
calcium
carbonate
calcium
sulphate
water
carbon
dioxide
See pages 238 - 239
Take the Section 5.2 Quiz
(c) McGraw Hill Ryerson 2007