Chemistry
Moles and equations
A)
Define and
use Mole calculations
One Mole: the
amount of substance that contains as many elementary entities as there are
carbon atoms in 12g of carbon-12
-Moles can be calculated using these equations:
-
Amount in moles = mass in grams / molar mass
= n =
m / M
-Amount
in moles = concentration x volume
= n = c x V
B)
Define
Avogadro’s number
Avogadro’s
number: the number of carbon-12 atoms in 12g of
carbon-12. Is equal to 6.022045 x 10²³
C)
Explain
and calculate Empirical and Molecular formula
Empirical
formula: gives the simplest whole number ratio of
the atoms of each element present in the compound.
Molecular
formula: gives the actual number of atoms of the
different elements in one molecule of a compound
-e.g
A compound contains
73.47% carbon, 10.2% hydrogen, and 16.33% oxygen. Its relative Molecular Mass
in 98. Calculate the empirical and molecular formulas of the compound.
Method:
1) Divide percentage of each element by the elements Atomic
mass
2) Divide all figures by the smallest calculated
3) Use this ratio to generate the empirical formula
4) Use the formula show to calculate how many times the
empirical formula goes into the molecular formal mass
5) Multiply the empirical formula by this number to calculate
the molecular formula
C H O
73.47/12 10.2/1 16.33/16
=6.1225 =10.2
=1.02
6.1225/1.02 10.2/1.02
1.02/1.02
=6 =10 =1
Empirical Formula : C₆H₁₀O
Molecular
Formula Mass = Empirical Formula Mass x n
98
= [(6 x 12) + (10 x 1) +
(16)] x n
98
= 98 x 1
1
x Empirical Formula = Molecular formula
1 x C₆H₁₀O = C₆H₁₀O
D)
Be able to
calculate percentage errors
Percentage error
= (maximum error / measurement taken) x 100
No comments:
Post a Comment