Transcript How to write up a practical: General review

Yr 10 Chemistry
Using the Mole in Calculations
Starter
 Hand back assessment
 New Assessment
 Read
 Create groups
 Decide on a topic
Objectives
 TO KNOW the term relative atomic
mass and mass number
 TO BE ABLE to calculate the
number of mass and number of
moles of substances.
 TO UNDERSTAND how to use the
periodic table to help.
Mass
 Atoms of different elements (or molecules,
particles, ions etc ) weigh differently because
they have different numbers of protons and
neutrons.
 So 1 mole of different elements will have
different masses.
Relative Atomic Mass (RAM)
 The RELATIVE Atomic Mass (A) of an element
indicates how heavy an atom of an element is
compared to an atom of a standard atom (C-12 is
used as this standard and is assigned a value of
exactly 12 g mol-1)
 So A(C) =12.01 g mol-1
 A(Cl) = 35.45 g mol-1
Relative Atomic Mass (RAM)
 Look at your periodic table……………….
 It turns out that:
 1 mole of Lithium (Li) = 6.94g
 1 mole of Nitrogen (N) = 14.01g
 Therefore 1 mole of elements = the RAM in
grams
Therefore, the Relative Atomic
Mass can also be seen as g/mole
Relative Molecular Mass (Mr)
 Many elements do not exist as single atoms but are
joined together in a MOLECULE.
 e.g Nitrogen (N) exists as a DIATOMIC MOLECULE (N2)
 So:
 Nitrogen has a relative atomic mass of 14.01 g mol-1
 Nitrogen has a relative molecular mass of 18.02 g mol-1
Molar Mass (M)
 The molar mass is very useful as it can be used
for any substance (e.g. atoms, molecules, ions,
compounds).
 It is determined by adding all masses of the
atoms in the compound.
 E.g M (CO2) = 12.01 + (2 x 16.00) =44.01 g mol-1
 ( one atom of carbon and two atoms of oxygen)
Note: for compounds it is sometimes
referred to as FORMULA MASS
 Calculate the formula mass of magnesium
carbonate, MgCO3.
24.31 g + 12.01 g + 3(16.00 g) = 84.32 g
Calculations
 This relationship cam be expressed as:
Relative Atomic
Mass (g/mole)
Mass (g)
M=m/n
 Or rearranged as:
m=nxM
Number of moles
 How many moles of lithium are in 18.2 grams
of lithium?
 How many atoms are present in 6g of Carbon