# Flex

## Flex

• Submitted By: flex94
• Date Submitted: 12/07/2010 3:47 AM
• Category: Science
• Words: 3167
• Page: 13
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Calculating the chemical formula

* The chemical ( molecular) formula of any compound gives us some information about the elements, type and number of atoms forming it.

* The chemical formula:
It is a simple symbolic form showing type and number of atoms in one molecule.
It also shows number of moles of each element in different compounds.

H2 O is the chemical formula of water.
It means that one molecule of water contains 2 atoms of hydrogen and 1 atom of oxygen.
It means that each mole of water contains 2 moles of hydrogen and 1 mole of oxygen.

Pb Br2 is the chemical formula of lead bromide.
It means that one molecule contains 1 atom of lead and 2 atoms of bromine.
It means that each mole contains 1 mole of lead ions and 2 moles of bromide ions.
The chemical formula of any compound can be calculated empirically.

Calculating the chemical formula:

1- Calculate the chemical formula of magnesium oxide if 0.24 gm of magnesium is
completely combusted in oxygen forming 0.4 gm of magnesium oxide, given:
Mg = 24 , O = 16.

Magnesium + oxygen magnesium oxide
0.24 x 0.4 gm
[pic] Mass of reacted oxygen = 0.4 – 0.24 = 0.16 gm.
Mg O
Mass of reacted sub. 0.24 0.16
Number of moles 0.24/24 0.16/16
= 0.1 0.1
Ratio of moles 1 : 1
[pic] The empirical or chemical formula is Mg O

2- Calculate the chemical formula of water if 4 gm of hydrogen is completely combusted in oxygen forming 36 gm of water given:
H = 1 , O = 16.

Hydrogen + oxygen water
4 x 36
[pic] Mass of...