Number
of moles of a substance =
|
mass
of substance in grams
|
relative
atomic or formula mass
|
Concentration
of solution, mol dm-3 =
|
number
of moles of solute
|
volume
of solution in dm3
|
Relative atomic
masses: H = 1, C = 12, O = 16, Na = 23, Mg = 24, Ca = 40, Br = 80, Ag =
108, Au = 197
1 The number of moles of atoms in 12g of
carbon and 108g of silver are the same. Explain this statement.
2 A pure gold wedding ring weighs 4g. How many
moles of gold atoms are there in the ring?
3 The ingredients label on a packet of salted
crisps says that it contains 0.23g of sodium. How many moles of sodium ions
does this represent?
4 What is the mass of 2 moles of calcium
carbonate?
5 A 0.75 dm3 bottle of ginger beer
contains 14.1g of sucrose, C12H22O11.
a What is the relative formula mass of the sucrose?
b How many moles of sucrose are in the ginger
beer?
c What is the concentration of the sucrose
in the ginger beer in mol dm–?
Extra challenge
6 A sample of magnesium bromide (MgBr2)
weighs 46g. How many moles of magnesium ions and bromide ions are in the
sample?
For tuesday 15th
The concentration of a solution is the mass of a solute, in
grams, dissolved in 1 dm3 of a solution. The units of concentration
are grams per decimetre cubed, g dm–3. The formula is shown below.
Concentration
(g dm–3) = mass of solute (g)
volume
of solution (dm3)
Remember that 1 dm3 is the same volume as 1 l
and 1000 cm3.
Try these questions. Show all your working.
1 A sample of sea water with a volume of 2 dm3
contains 60 g of salt dissolved in it. What is the concentration of salt
in the sea water?
2 A bottle of ginger beer contains 28 g
of sugar in a 0.25 dm3 portion. What is the concentration of
sugar in the ginger beer?
3 The laboratory technician made up some
limewater for use in chemistry experiments. She dissolved 15 g of calcium
hydroxide in water to make up 2 l of solution. What is the concentration
of the limewater?
4 Kyle dissolved a cube of sugar with a
mass of 3 g in a 100 cm3 cup of coffee. What is the
concentration of sugar in Kyle’s coffee?
5 A 1 l bottle of mineral water contains
28 mg of calcium. What is the concentration of calcium
in g dm–3?
in g dm–3?
6 An Olympic-sized swimming pool has a
volume of 2.5 × 106 dm3.
10 kg of chlorine is needed to disinfect the pool. What is the
concentration of chlorine in the water in g dm–3?
Homework for tuesday 3rd november:
For each substance below:
· find the molecular formula using reference books or the Internet
· if the relative formula mass is given, show how you can prove this
· give a common use for the substance.
1 aspirin
2 citric acid
3 ethanoic acid
4 ethanol
5 paracetamol
6 phosphoric acid
7 potassium nitrate
8 trinitrotoluene (TNT)
Present your results in a table.
Extra challenge
9 The formula for a compound X is CH3(CH2)7CH=CH(CH2)7CO2H.
a Work out the molecular formula of this compound.
b Calculate the relative formula mass of the compound.
c Deduce the empirical formula of the compound.
d Find out the name of the compound.
e Explain why this compound has been described as ‘the smell of death’.
Make a c2.1, c2.2, c2.3, c2.4 revision poster.
Incude all detail you can! make it as detailed as possible, you will need this for your revision in a few months time! For Tuesday 22nd September :)
CUS
Write a page research on the subject of "How does the chemical industry minimise waste and make a profit?"
use examples, processes and ideas. for Next Tuesday
