Chemical Equations and Tests
for anions
Chemical Reactions
• Whenever two elements combine to form
a compound a chemical reaction has
taken place
• In a chemical reaction the starting
substances are called the Reactants and
the substances formed are called the
Products
Word Equations
• We generally wrote chemical reactions in
words as word equations
Carbon + Oxygen
Carbon Dioxide
Can you identify the reactants and products
above?
Chemical Equations
• We can also use the chemical symbols of
the substances to describe the chemical
reaction that has taken place
C + O2
CO2
The reactants are written on the left of the arrow and the products on
the right this is generally always the case
The arrow sign means “react to give” the + sign means “and”
Balancing Chemical Equations
• French Chemist
Antoine Lavoisier
found that the total
mass of products is
always equal to the
total mass of
reactants
Law of Conservation of Mass
The total mass of the products of a
chemical reaction is the same as the total
mass of the reactants
For example if 12 grams of Carbon dioxide
react with 32 grams of oxygen 44 grams of
carbon dioxide will be formed
Law of Conservation of Matter
In any chemical reaction matter is neither
created nor destroyed but merely changes
from one form to another
If there is a particular number of atoms at
the start of a reaction then there must be
the same number of atoms at the end of
the reaction
• Is the equation balanced?
C + O2
CO2
How many C atoms are there on the left?
How many are on the Right?
How many O atoms are on the Left?
How many are on the right?
Remember when balancing
Equations
• You may adjust the number in front of the
atoms/molecules, but you may not change
the formula by changing the small number
after an atom
• This method of balancing equations is
known as balancing by inspection practice
with question 6.1 (a) to (n) on p77
Tests for Anions in Aqueous
Solutions
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•
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1.
2.
3.
4.
5.
6.
7.
Negative ions are also known as anions
You learned off some common anions in chapter 5
The ions we will test for are :
Chloride ion (Cl-)
Sulfate ion (SO42-)
Sulfite ion (SO32-)
Carbonate ion (CO32-)
Hydrogencarbonate ion (HCO3-)
Nitrate ion (NO3-)
Phosphate ion (PO43-)
• Because we are only testing to see if
these anions are present and not to see
how much of them is present this is known
as Qualitative analysis
• Testing to see how much of a substance is
present is known as Quantitative analysis
The various tests for anions are
summarised in this table