Transcript Structures and Bonding

17/07/2015
Chemical Synthesis
W Richards
The Weald School
The pH scale
17/07/2015
The pH scale is a way of showing how strong or weak an acid or
alkali is:
1
2
3
Stomach acid
4
5
Lemon juice
6
7
8
9
10
11
12 13 14
Water Soap Baking powder Oven cleaner
Strong alkali
Strong acid
Neutral
An acid contains hydrogen ions, H+
An alkali contains hydroxide ions, OH-
Common acids and alkalis
17/07/2015
Acids
Alkalis
Hydrochloric acid, HCl
Sodium hydroxide, NaOH
Nitric acid, HNO3
Potassium hydroxide, KOH
Sulphuric acid, H2SO4
Magnesium hydroxide, Mg(OH)2
Calcium hydroxide, Ca(OH)2
Neutralisation reactions
17/07/2015
When acids and alkalis react together they will NEUTRALISE
each other:
Sodium hydroxide
Na
Hydrochloric acid
H
OH
The sodium “replaces”
the hydrogen from HCl
Na
Cl
Sodium chloride
General equation:
H2O
Water
H+(aq) + OH-(aq)
H2O(l)
Cl
Neutralisation experiment
17/07/2015
For example, in a neutralisation experiment we can mix sodium
hydroxide (an _____) and hydrochloric acid together and they
will ________ each other. The equation for this reaction is…
Sodium hydroxide + hydrochloric acid
sodium chloride + water
A ____ was formed during the reaction, and we could have
separated this by __________ the solution. The salt that we
formed depended on the acid:
• Hydrochloric acid will make a CHLORIDE
• Nitric acid will make a _________
• Sulphuric acid will make a _________
Words – nitrate, neutralise, alkali, sulphate, salt, evaporating
Neutralisation reactions
17/07/2015
The basic equation for any neutralisation reaction is:
H+(aq) + OH-(aq)
H2O(l)
Write word and chemical equations for the following reactions:
1) Hydrochloric acid + sodium hydroxide
2) Hydrochloric acid + potassium hydroxide
3) Nitric acid + potassium hydroxide
4) Sulphuric acid + calcium hydroxide
5) Nitric acid + copper oxide, CuO
6) Sulphuric acid + calcium carbonate, Ca(CO)3
Making salts
17/07/2015
Whenever an acid and alkali neutralise each other we are left
with a salt, like a chloride or a sulphate. Complete the
following table:
Hydrochloric
acid
Sodium
hydroxide
Potassium
hydroxide
Calcium
hydroxide
Sulphuric acid
Nitric acid
Sodium chloride +
water
Potassium
sulphate + water
Calcium nitrate +
water
Balancing ions revision
Some common ions:
Sodium – Na+
Chloride – Cl-
Potassium – K+
Bromide – Br-
Magnesium – Mg2+
Oxide – O2-
Ammonium – NH4+
Sulphate – SO42-
Determine the formula of the following compounds:
1) Sodium chloride
2) Magnesium oxide
3) Magnesium chloride
4) Ammonium chloride
5) Sodium sulphate
6) Sodium oxide
17/07/2015
Simple formulae to learn
17/07/2015
H2O
Water
NaCl
Sodium chloride
CO2
Carbon dioxide
CCl2
Calcium chloride
NH3
Ammonia
MgO
Magnesium oxide
H2
Hydrogen
HCl
Hydrochloric acid
O2
Oxygen
NaOH
Sodium hydroxide
N2
Nitrogen
Ca(OH)2
Calcium hydroxide
SO2
Sulphur dioxide
CaCO3
Calcium carbonate
Atom Economy
% yield
=
Actual yield
Theoretical yield
17/07/2015
X 100%
Calculate the % yields of the following:
1) An experiment that should have extracted 12g of aluminium
but only extracted 7g.
2) An experiment that should have produced 20g of zinc
chloride but only produced 5gg instead.
3) Another experiment has a yield of 60%. If 20g of the
product was possible how much was actualy made?
Chemical Synthesis
17/07/2015
In the manufacture of an inorganic compound the following
stages can be used:
1) Work out the reactions that need to be done
2) Carry out a risk assessment
3) Calculate the quantities of reactants to use
4) Do the reaction
5) Separate the product from the mixture
6) Purify it
7) Measure the yield
8) Check its purity
Atomic mass
17/07/2015
RELATIVE ATOMIC MASS, Ar
(“Mass number”) = number of
protons + number of neutrons
SYMBOL
PROTON NUMBER = number of
protons (obviously)
Relative formula mass, Mr
17/07/2015
The relative formula mass of a compound is the relative atomic
masses of all the elements in the compound added together.
E.g. water H2O:
Relative atomic mass of O = 16
Relative atomic mass of H = 1
Therefore Mr for water = 16 + (2x1) = 18
Work out Mr for the following compounds:
1) HCl
H=1, Cl=35 so Mr = 36
2) NaOH
Na=23, O=16, H=1 so Mr = 40
3) MgCl2
Mg=24, Cl=35 so Mr = 24+(2x35) = 94
4) H2SO4
H=1, S=32, O=16 so Mr = (2x1)+32+(4x16) = 98
5) K2CO3
K=39, C=12, O=16 so Mr = (2x39)+12+(3x16) = 138
17/07/2015
Calculating the mass of a product
E.g. what mass of magnesium oxide is produced when 60g of
magnesium is burned in air?
Step 1: READ the equation:
2Mg + O2
2MgO
IGNORE the
oxygen in step 2 –
the question
doesn’t ask for it
Step 2: WORK OUT the relative formula masses (Mr):
2Mg = 2 x 24 = 48
2MgO = 2 x (24+16) = 80
Step 3: LEARN and APPLY the following 3 points:
1) 48g of Mg makes 80g of MgO
2) 1g of Mg makes 80/48 = 1.66g of MgO
3) 60g of Mg makes 1.66 x 60 = 100g of MgO
1) When water is electrolysed it breaks down into hydrogen and17/07/2015
oxygen:
2H2O
2H2 + O2
What mass of hydrogen is produced by the electrolysis of 6g of water?
Work out Mr:
1.
2H2O = 2 x ((2x1)+16) = 36
2H2 = 2x2 = 4
36g of water produces 4g of hydrogen
2. So 1g of water produces 4/36 = 0.11g of hydrogen
3. 6g of water will produce (4/36) x 6 = 0.66g of hydrogen
2) What mass of calcium oxide is produced when 10g of calcium burns?
2Ca + O2
Mr: 2Ca = 2x40 = 80
2CaO
2CaO = 2 x (40+16) = 112
80g produces 112g so 10g produces (112/80) x 10 = 14g of CaO
3) What mass of aluminium is produced from 100g of aluminium oxide?
2Al2O3
4Al + 3O2
Mr: 2Al2O3 = 2x((2x27)+(3x16)) = 204
4Al = 4x27 = 108
204g produces 108g so 100g produces (108/204) x 100 = 52.9g of Al2O3
Another method
17/07/2015
Try using this equation:
Mass of product IN GRAMMES
Mass of reactant IN GRAMMES
Mr of product
Mr of reactant
Q. When water is electrolysed it breaks down into hydrogen and oxygen:
2H2O
2H2 + O2
What mass of hydrogen is produced by the electrolysis of 6g of water?
Mass of product IN GRAMMES
6g
4
36
So mass of product = (4/36) x 6g = 0.66g of hydrogen
Titration
17/07/2015
1) Fill a burette with sodium hydroxide
solution of known concentration
2) Accurately measure out 25cm3 of acid
and place it in the conical flask
3) Add phenolphthalein indicator to the
flask
4) Slowly add the alkali until the mixture in
the flask turns pink
5) Repeat until you get similar results
Measuring the Rate of Reaction
17/07/2015
Three common methods:
Measuring the Rate of Reaction
17/07/2015
Three common methods:
Rate of reaction graph
Amount of
product
formed/
reactant
used up
Fast rate
of reaction
here
17/07/2015
Slower rate of reaction here
due to reactants being used up
Slower reaction
Time
Rate of reaction graph
17/07/2015
Q. What if less reactants were used?
Amount of
product
formed/
reactant
used up
Time
Rates of Reaction
17/07/2015
Oh no! Here comes
another one and it’s
got more energy…
Here comes another
one. Look at how slow
it’s going…
It missed!
Here comes an acid particle…
No effect! It didn’t
have enough energy!
Hi. I’m Mike Marble. I’m
about to have some acid
poured onto me. Let’s see
what happens…
Rates of Reaction
17/07/2015
Chemical reactions occur when different
atoms or molecules _____ with enough
energy (the “________ Energy):
View animation
Basically, the more collisions we get the _______ the
reaction goes. The rate at which the reaction happens
depends on four things:
1) The _______ of the reactants,
2) Their concentration
3) Their surface area
4) Whether or not a _______ is used
Words – activation, quicker, catalyst, temperature, collide
Catalyst Summary
17/07/2015
Catalysts are used to ____ __ a reaction to increase the rate
at which a product is made or to make a process ________.
They are not normally ___ __ in a reaction and they are
reaction-specific (i.e. different reactions need _________
catalysts).
Words – different, speed up, used up, cheaper
Rate of reaction graph - catalysts
17/07/2015
Amount of
product
formed/
reactant
used up
With catalyst
Without
catalyst
Time