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Unit 1 ­ Amount of Substance

Formula of Ionic Compounds

H+ Ba2+ Fe3+ Cl- O2-
Na+ Ca2+ Al3+ Br- S2-
Ag+ Cu2+ F- SO42-
K+ Mg2+ I- CO32-
Li+ Zn2+ HCO3-
NH4+ Pb2+ OH-
Fe2+ NO3-

Relative atomic Mass (Ar)
The weighted average mass of an element, taking into…

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Unit 1 ­ Amount of Substance

Molecular Formula
Gives us the actual number of each type of atom in a molecule

Empirical Formula
The formula used to represent the simplest ration (by mole) of atoms in a compound.

Finding Empirical Formula

Element A B
Mass (g) a X
Mass of…

Page 3

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Unit 1 ­ Amount of Substance

p = pressure (Pa)
V= volume (m3)
n= number of moles
R= gas constant = 8.31
T=temperature (kelvins)

1 kPa=1000Pa
kPa x 1000 = Pa

1m3 = 1000 dm3 = 1,000,000 cm3
cm3 / 1,000,000 = m3
dm3 /1000 = m3

Page 4

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Unit 1 ­ Amount of Substance

step one ­ balance equation
step two ­ use mass or conc X vol(dm3) to find the number of moles in the first substance
step three ­ use ration from the equation to find the number of moles in the other substance

Page 5

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Unit 1 ­ Amount of Substance

You can then work out a percentage yield using
Percentage Yield = actual yield .
Theoretical yield

Reasons why a yield may be low:
Reaction may be incomplete (perhaps it is slow, or reaches equilibrium state) so a portion of
the starting chemicals fail…

Page 6

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Unit 1 ­ Amount of Substance

The number of significant figure of the result should be equal to that of the quantity that
contains the least number of significant figures.

In General
The uncertainty in a single measurement from an instrument is half the value of the smallest



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