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(C6) OCR 21st Century GCSE: Chemical Synthesis

The Chemical Industry - Acids & Alkalis - Neutralisation - Titrations - Testing Purity - Exothermic & Endothermic - Reaction Rate - Concentration - Temperature - Surface Area - Pressure - Catalysts - Collision Theory - Theoretical & percentage yield
by

J Amuah-Fuster

on 8 July 2016

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Transcript of (C6) OCR 21st Century GCSE: Chemical Synthesis

YOU NEED A CALCULATOR!




To do…
Complete the relay race.
Pair 1 completes the first question to find answer A
Pair 2 use answer A to calculate B.
Pair 1 uses answer B to calculate C
Pair 2 uses answers C to find D
3+
2+
From the pictures of molecules, work out their chemical formulae:
a) b) c)


What are the formulae of these antacids?
Magnesium hydroxide (made up of magnesium ions, Mg , and hydroxide ions, OH-).
Aluminium hydroxide (made up of aluminium ions, Al , and hydroxide ions, OH-).
L1: The Chemical Industry
Chemicals have many uses, including the preservation of food, treatment of diseases, and building and decorating of our homes.

Many of these compounds are not found naturally - they are synthesised in chemical factories, called
plants
. Acids and alkalis are some of the most widely used chemicals both in industry and our homes.

Chemical reactions that occur can give out energy or take energy in.
L2 & 3: Acids, Alkalis & Indicators
Hazards!!!
L4: Neutralisation
What happens when an acid meets an alkali?
L6: Titrations
testing purity
L7: Exothermic & Endothermic
Synthesis
Chemical
C6
Atoms are rearranged during chemical reactions.
The number of atoms of each element stays the same in a chemical reaction.
Raw materials can be used to make stnthetic materials.
Alkalis neutralise acids to make salts.
Chemical reactions can be represented by word equations and balanced symbol equations.
Some substances are made up of electrically charged particles called ions.
Data is ore reliable if it can be repeated.
What you already know
the importance of the chemical industry
a theory to explain acids and alkalis
reactions that give out and take in energy
techniques for controlling the rate of chemical change
the steps involved in the synthesis of a new chemical
ways to measure the efficiency of chemical synthesis
Find out about
Bulk Chemicals
Fine Chemicals
The chemical industry makes bulk chemicals on a huge scale of thousands or even millions of tonnes per year. These include chemicals such as; ammonia, sodium hydroxide, chlorine and ethene.
Fine chemicals, such as; drugs, herbicides and pesticides are produced on a much smaller scale. This is because they are usually needed by other manufacturers for other purposes, e.g. LCD screens, food additives and flame retardants
Control & Monitor
Industrial processes need to be controlled in order to prevent waste or dangerous incidents. In all areas of the plant, data is recorded and fed to computers in the control centre where technical teams can respond.
Questions
Classify the following as raw materials or products of the chemical industry:
Air, Ammonia, Aspirin, Crude oil, Polythene, Water

Give the name and formula of a bulk chemical.

List these chemicals under bulk chemical or fine chemical:
Aspirin
(drug),
Ethene
(hydrocarbon),
Citral
(perfume chemical),
sulfuric acid
(chemical),
glyphosate
(herbicide),
sodium

hydroxide
(chemical),
carotene
(food dye)
Other chemical plant workers
Every chemical plant needs managers and administrators to control the whole operation, as well as staff to keep the plant and its staff at optimum performance.
People in the Chemical Industry
Works in the plant and the laboratory to find new processes and develop new products
Research Chemist
Marketing & Sales
Compare the cost of making the new product with the estimated value of it.
This helps them to decide if the product is viable, and therefore profitable.
Financial experts
These workers have to scale everything up to achieve mass production volumes. This can cost up to hundreds of millions of pounds.
Chemical Engineers
Some chemicals that are used in other processes need to be specially transported by qualified personnel.
Transport workers
Managers
Administrators
Plant operators
Maintenance
Catering
Medical
Safety
Training
Decide if new product is in demand.
If promising, a pilot plant is set up to make small amounts of the product.
Questions
Acids
Acids sound like dangerous chemicals, and they can be
corrosive
if very concentrated.
When diluted, acids are less hazardous and can be essential to life, such as
citric acid
.
Organic Acids
These are
molecular
acids. Made up of groups of atoms, they consist of carbon, hydrogen, and oxygen atoms.
They are acidic due to the H atom in the -COOH group.
Ascorbic (vitamin C), Citric (in citrus fruits) and tartaric acids are solid organic acids. Ethanoic acid (vinegar) is a liquid organic acid.
Mineral acids
Sulfuric, nitric, and hydrochloric acids are inorganic, they come from mineral raw materials.
The pure acids are molecular compounds; with sulfuric and nitric acid being liquids, whilst hydrogen chloride is a gas.
The latter becomes hydrochloric acid when it is dissolved in water.
Pharmacists can control heartburn and acid indigestion using chemicals that are the
opposite

of the acid
in our stomachs and they
neutralise
it.
These are usually solid tablets, but antacids can be soluble. If so, we call them
alkalis
.
Common alkalis are sodium hydroxide, NaOH; and calcium hydroxide, Ca(OH)
Alkalis
2
Alkalis can be dangerous too. Concentrated alklais are said to be
caustic
meaning they can burn away flesh if in contact for some time
Indicators
&
The pH scale
Indicator are chemicals that change colours to show whether a solution is acidic or alkaline.
Blue litmus turns red in acidic conditions.
Red litmus turns blue in alklaine conditions.
Special mixed indicators show a range of colours that can be used to estimate pH values.
Their use gives us an estimate of the acidity or alkalinity, as we normally judge the colour by eye.
pH values can be measured using a pH meter with an elctrode dipped in the solution. This gives a more pecise reading, leading to more accurate pH values.
The pH scale is a number scale that shows the acidity or alkalinity of a solution in water. It ranges from 1-14 for most sulutions.
Citric acid is a weak acid. A solution of citric acid has some universal indicator added to it. What would you observe?

Suggest some pH values for the following substances:
Lemon juice, Soapy water, Bleach, Baking soda, Distilled water, and Hydrochloric acid

Hydrochloric acid reacts with excess zinc metal. All the acid is used up. What is the pH of the solution?
Questions
Reactions of Acids
Acids with metals
Acids react with
metals
to produce
salts
. The other product is
hydrogen

gas
.
Acids with metal oxides or hydroxides
Acids react with a
metal oxide
or
hydroxide
to form a
salt
and
water
.
No gas forms
.
Acids with carbonates
Acids react with
carbonates
to form a
salt
,
water
, and bubbles of
carbon dioxide gas
.
This is often a vital step in extracting metals form ores.
Geologists use this to test for carbonates.
By dripping hydrochloric acid on the sample, if they notice any fizzing, then carbonates are present in the rock.
L5: Explaining neutralisation
When gunpowder burns, is the rate of reaction high or low?

Which has the higher reaction rate, zinc reacting with sulphuric acid, or cement setting?

Give four ways of making a reaction between a solid and a liquid go faster.
Fast reactions have
high
rates of reaction



Slow reactions have
low
rates of reaction
Lesson Objectives:
chemical reactions occur at different times
the factors affecting reaction rates
how to measure reaction rates
What does the 'rate' mean?
= =
amount of reactant used up
amount of product formed
time taken
time taken
fewer reactants
are turned into
products
and it takes a
longer time
lots of reactants
are turned into
products
in a
very short amount of time
Altering Reaction Rates
4 factors can affect the rate
Surface Area
Increasing
Concentration
Increasing
Pressure (of gases)
Increasing
Temperature
Collision Theory
States:
to successfully react, particles must
collide with sufficient energy
(
activation energy
)

more successful collisions per unit time (seconds), mean a
higher frequency of successful collisions

this leads to a
faster

rate of reaction
reactant particles have more energy (gain kinetic energy)

particles move faster (and collide with more energy)

The frequency of successful collisions is greater
Number of reactant particles increases per unit of volume.

less space for particles to move freely

The frequency of successful collisions is greater
This
only
works on
gaseous reactants.
Like concentration, there are
more particles
per unit of volume
Less space for particles to move freely
More

frequent successful collisions.
Using smaller particles of a solid, the same mass can have a greater surface area, where collisions occur.

This increases the number of successful collisions
Catalysts
Catalysts change the pathway of the chemical reaction.

They take part in reactions, but are
not used up
, so they can be recovered and used again

Adding a catalyst
does not affect the number of collisions

A catalyst makes the reaction easier by
lowering the activation energy
. Thus, the
proportion of successful collisions is higher
.
Measuring the Rate of Reaction
Measuring the reaction rate needs two measurements:
Quantity - of reactant used or product made
Time
Experimental Methods
Time a solid reacting to give a solution
Weigh a solid and time how long it takes to react completely
Measuring mass and time only once gives an average reaction rate
Measure the volume of gas given off
Connect the apparatus to a gas syringe or upturned measuring cylinder. Read the volume of gas evolved at known times.

This allows comparison of the
initial reaction rate
with rates at other stages of the reaction.
Weigh the gas given off
Stand the apparatus on a top-pan balance. Taking readings at regular intervals. As gas is given off, the mass of the mixture decreases. the decrease equals the mass of gas given off.

This allows comparison of the
initial reaction rate
with rates at other stages of the reaction
Calculating Reaction Rates [HT]
Units
For
quantity
, units may be
grams (g)
or
centimetre cubed (cm3)
.

For
time
, units may be
seconds (s)
or
minutes (min)
.
Changing rates
As reactants are used up in a proceeding reaction, the reaction rate slows down - eventually to zero.

When the reaction is complete, the quantity of reactant or product will
remain constant
.
Worked Examples
Limestone reacting with acid
Magnesium reacting with acid
8.0 cm3 of hydrogen is given off in the first 30 seconds (or half a minute).

Initial
reaction rate = 8.0/30 = 0.27 cm3/s
or 8.0/0.5 = 16 cm3/min of hydrogen
(from the graph)
0.9g of limestone completely reacts with acid in 7.5 minutes (450s).

Average
reaction rate = 0.9/7.5 = 0.12 g/min
or 0.9/450 = 0.002 g/s of limestone
E Grade
C Grade
A Grade
Suggest why reaction rates decrease as the reaction proceeds?
How could you make a balance read the mass of gas given off
directly
(without need for calculation)?

When measuring the volume of gas, using an upturned burette would
increase the accuracy
, but would be
more difficul
t. Explain why.

Explain what an
initial
reaction rate means.
Collision Theory
E Grade
Collision Theory
C Grade
Collision Theory
A Grade
Does magnesium react faster with
hot
or
cold
hydrochloric acid?

Give
three
ways to speed up a reaction between nitrogen gas and hydrogen gas.

If iron
powder
is burnt in a Bunsen burner, how will the reaction compare to when solid iron
nail
is burnt in a Bunsen burner.
Describe how an increase in temperature will affect the rate of a chemical reaction.

Explain how diluting an acid solution would affect the reaction rate when it reacts with marble chips?
Describe how you would carry out an experiment to investigate the effect of acid concentration on how long it takes for a piece of magnesium to disappear.

Explain why 1 g of powdered zinc reacts with acid much faster than a 1 g lump

Explain how catalysts are useful when trying to make chemical reactions more sustainable.
Rate of reaction
http://www.bbc.co.uk/education/guides/zwdp34j/video
Blue litmus paper turns _____ in acidic solutions
The pH scale (1 – 14) shows the acidity or the alkalinity of any solution in water.
A solution with a pH less than 7 is ________ (getting more red), more than 7 is ________ (getting more purple) and equal to 7 is _________ (green)
Balance the
symbol equations
for Qn 1 -3 on the ‘completing equations’ work sheet
Turns from yellow in alkali to _______ in acid
Recall that indicators change colour in acidic and alkaline conditions

Recall the shape of the graph when an acid is added to an alkali

Write word and symbol equations for neutralisation reactions
Now try to write the chemical formula for each
cdhrocyhlori ciad
lricusfu aidc
nircti acdi
iumsod roxihyde
imclacu rdodxiyeh
ssopiuamt yoxdirhde
Lesson Objectives
Indicators
At the start, the pH of the mixture is high, because there is an excess (mostly) of alkali solution present.
As more acid is added to the alkali, some of the alkali is being
neutralised
, but the alkali is still in excess.
Eventually, the amount of
acid
added becomes
equal
to the amount of
alkali
used at the start.

It shown by the pH
changing suddenly
.
As we add the rest of the acid, there is now more acid than alkali.

The pH is now low, because there is an ecess of acid present.
The
drastic change
in pH shows us where one solution is
neutralised
by the other.
The mid-point of this drastic change is called the
equivalence point
.
Neutralisation on a pH curve
Write symbol equations for the above reactions. Use the charges on the following ions to help you:
O

Cl H Mg
NO OH Li Ca
CO K
SO Na

Naming salts
Neutralisation reactions
Have a go at answering the following:-

What is an acid?
What is an alkali?
What happens in a neutralization reaction?

Try to come up with definitions not just examples
Explaining Neutralisation
All acids dissolve in water to make __________ ions.
All alkalis dissolve in water to make ____________ ions.
Acids and alkalis react together to make a _______ and ________. This is because:


H+ + OH- ________

Copy and complete
A strong acid has a pH of 6/7
Acids react with water to produce hydrogen ions
In a neutralisation reaction a salt and hydrogen are made
A neutral solution is pH 7
To do an acid/alkali titration you use a burette
A weak alkali has a pH of 13/14
Alkalis react with water to produce hydrogen ions
In neutralisation reactions hydrogen ions and hydroxide ions react together to form water
True
or
false
?
Explain what happens when acidic and alkaline compounds dissolve in water

Explain how water is formed during a neutralisation reaction

Know how to work out the formula of the salt produced given the formula of the acid and the alkali
Learning Outcomes
Acid + alkali salt + water
HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)

H+ + OH- H2O
Alkalis contain hydroxide ions (E.g. NaOH)
Alkalis form OH- ions in water
Acids contain hydrogen (E.g. HCl)
Acids from H+ ions in water
Neutralisation occurs when
alkalis
(e.g.
sodium hydroxide
) react with
acids
(e.g.
hydrochloric acid
) to produce
water

(e.g.
hydrogen

hydroxide
) and

a
metal

salt
(e.g.
sodium

chloride
).
Neutralisation reactions
acid (aq) + metal (s) salt (aq) + hydrogen (g)

acid (aq) + metal oxide (s) salt (aq) + water (l)

acid (aq) + metal hydroxide (aq) salt (aq) + water (l)

Making salts

Hydrochloric
acid makes a metal
chloride

Nitric
acid makes a metal
nitrate

Sulfuric
acid makes a metal
sulfate
REMEMBER
 
Example: 
hydrochloric
acid +
sodium
hydroxide
sodium

chloride
+ water
1. sulphuric acid + potassium hydroxide
2. nitric acid + sodium hydroxide
3. hydrochloric acid + calcium hydroxide
4. nitric acid + magnesium hydroxide
5. sulphuric acid + magnesium hydroxide
4
2-
3
Look at the neutralisation reactions below.


hydrochloric acid + sodium hydroxide sodium chloride + water

lithium oxide + nitric acid lithium nitrate + water



T
T
T
F
F
F
F
T
-
-
-
potassium carbonate + sulphuric acid potassium sulphate + water + carbon dioxide
Standardised assessment Qn 6 & 7
OLD STYLE QN
What is your best estimate of the purity of the citric acid sample?

Suggest a reason why all members of the class did not get exactly the same results.

Decide whether there are any outliers in the data. If there is an outlier, circle it. Can the outlier be explained (eg was a mistake made when using the equipment)?

Use the remaining results to work out the mean and the range.

Why is it better to find the mean of the class results instead of just using your own results?
Summary - things to consider
A
burette
is filled with a solution up to the
zero mark
using a
funnel
.

TODAY: SODIUM HYDROXIDE

This solution will react with the chemical being analysed.

The concentration of this solution is known.
Titrations are used for chemical analysis:
to find the purity of a solid chemical
to find the concentration of a solution.
Standardised assessment Qn 6

Recording results
At the end point the
indicator changes colour
.

The scale on the burette shows the volume of solution that has been added.

This is the titre.
RECORD THIS
.

A calculation gives the purity or concentration of the sample being analysed.
Making your results accurate:

swirl the flask so all the contents mix

add your solution drop by drop (after you have done a range finder)
The solution in the burette is added to the contents of the flask, while the flask is swirled constantly.

Near the end point the solution is added drop by drop.
An
indicator
(3-4 drops) is added to the solution being analysed.

TODAY: PHENOLPHTHALEIN.

This will change colour when the reaction is complete.
A sample of the chemical being analysed is placed in a conical flask.
If a solid, a
balance
is used to accurately
measure its mass
.
It is then
dissolved in pure water
.

TODAY: CITRIC ACID SOLID
.

If the chemical being analysed is a solution, its volume is measured accurately using a
graduated pipette
.
There will be an exam question on this!
To perform a titration to find out if the citric acid is pure

To use a formula to check if the citric acid is pure

Describe how to perform a titration
Lesson Outcomes
Why is purity important?
Purity of a chemical is important because if it is impure there may be ch________s present that could cause h____.

C6 L5: Testing purity

Add a few drops of phenolphthalein indicator
Person 1
Person 2
Fill the burette with sodium hydroxide (NaOH)
Measure out 50 ml of water using a measuring cylinder and add it to the citric acid .
Stir to dissolve.
Weigh out 0.5 g of citric acid
Run the sodium hydroxide into the citric acid. Stop when it permanently changes colour. Record this volume.
This is the range finder.
Now repeat the experiment but add the sodium drop by drop at the end to get an accurate reading.
Titrations in industry are often carried out by robots.
The robots transfer the solutions, measure volumes and detect the end point.
OLD STYLE QN
OLD STYLE QN
We test for hydrogen using the 'squeeky pop' test
Step 1
Step 3
Step 2
Exam Style questions
Step 4
Step 5
Carrying out a titration
2-
2-
2+
2+
+
+
+
+
Can you name these compounds?
Reactions of Acids and Alkalis
Watch demos / perform practicals and make notes on your observations
Mg (s) + HCl (aq) MgCl (aq) + H (g)


CuO (s) + HCl (aq) CuCl (aq) + H O (l)



HCl (aq) + CaCO (s) CaCl (aq) + H O (l) + CO (g)
Magnesium + hydrochloric acid



Copper Oxide + hydochloric acid



Hydrochloric acid + calcium carbonate
Write a
word equation
for each reaction, then a
balanced symbol equation
(
Include state symbols!!!
)
Turns from ___________ in acid to ______ in alkali.
alkali
acid
alkali
acid
alkali
acid
Acids are neutralised in different ways by different bases:
acid (aq) + metal carbonate (s) salt (aq) + water (l) + carbon dioxide (g)
Acid + alkali salt + water
HCl(aq) + NaOH(aq) NaCl(aq) + H O(l)
2
2
2
2
2
2
2
2
3
magnesium chloride + water



coppper chloride + water



calcium chloride + water +
carbon dioxide
What is an indicator?

Explain what happens to the pH of an acidic solution as alkali is added to it.

What compound is always produced during a neutralisation reaction?
Petrol burning
-
EXO
as combustion reaction produces hot gases to drive engines
Water turning to steam
-
ENDO
as takes in energy when heating
Photosynthesis
-
ENDO
as it takes energy from the sun
Magnesium and hydrochloric acid
-
EXO
as reaction mixture gets hotter
Respiration
-
EXO
as the reaction between oxygen and glucose gives out the energy for growth, warmth and movement
Petrol burning
Water turning to steam
Photosynthesis
Magnesium and hydrochloric acid
Respiration
Energy changes in an endothermic reaction
This requires you to read the instructions and follow them carefully

Highlight any pieces of equipment you are going to need
Get goggles and your equipment
Record the results

define the terms
exothermic
and
endothermic

represent
energy changes
using
diagrams
Add 10 ml of 1 M HCl in a boiling tube
Put ½ spatula of Mg into the boiling tube

Write down
all
your observations
surroundings get colder
surroundings get hotter
Reactions
do not create or destroy energy.
They
transfer
it
to or from their surroundings
.
magnesium + hydrochloric magnesium + hydrogen
acid chloride

Energy changes in an exothermic reaction
Energy changes are shown using an
energy level diagram
.
Energy changes in an exothermic reaction
Energy is
given out
during this reaction.
It is an
exothermic
reaction.
Magnesium ribbon reacting with hydrochloric acid

ammonium nitrate (s) ammonium ions (aq) + nitrate ions (aq)

water
Ammonium nitrate dissolves to form a solution of ammonium and nitrate ions.
It is an
endothermic
process.
Energy is taken in

from the surroundings
. The flask
cools
and is frozen to the block of wood.
Ammonium nitrate dissolves in water
Endothermic
Exothermic
A reaction
takes in
energy from the surroundings (
feels cold
)
A reaction
gives out
energy to the surroundings (
feels hot
)
Person 1
Person 2
DIVISION OF LABOUR
Extension: Write symbol equations for the above reactions
Write
word equations
to show the products of the following reactions:

Sodium carbonate and nitric acid
Magnesium oxide and hydrochloric acid
Potassium and sulphuric acid
Starter - writing equations
How to test the purity of citric acid
Use the table above to write the chemical formula for:

1. Sodium chloride 5. Calcium chloride
2. Magnesium carbonate 6. Lithium carbonate
3. Potassium sulphate 7. Potassium nitrate
4. Magnesium nitrate 8. Sodium sulphate
A
F D B C E
Negative ions Positive ions
O

Cl H Mg
NO OH Li Ca
CO K
SO Na

4
2-
3
-
-
-
2-
2-
2+
2+
+
+
+
+
3
Starter - writing formulae
Malachite
Copper carbonate ore
Copper Sulphate solution
react with sulphuric acid
Limewater
reacts with carbon dioxide - turning
cloudy/milky
.
Carbonates reacting with acid, producing carbon dioxide gas.
Antacid remedies to treat indigestion
Chlorine gas
Hydrogen gas
Nitrogen gas
Oxygen gas
Hydrochloric acid
Nitric acid
Sulphuric acid
Sodium hydroxide
Sodium chloride
Sodium carbonate
Potassium chloride
Magnesium oxide
Magnesium carbonate
Magnesium sulphate
Calcium carbonate
Calcium chloride
Universal Indicator & the pH Scale
Litmus paper
Methyl Orange
Pheolphthalein
acid
neutral
alkali
red
red
pink
colourless
Running acid into alkali
Running acid into alkali
Running acid into alkali
Running acid into alkali
Acid + metal carbonate
Acid + metal oxide
Acid + metal
Exothermic
&
Endothermic
Reactions
Lesson Outcomes
What energy changes are happening here?
What did you observe?
Citric acid + sodium hydrogen carbonate + water
bubbles of gas released
felt cold
bubbles of gas released
felt hot
What did you observe?
Energy is
taken in
during this reaction.
It is an
endothermic
reaction.
Energy changes are shown using an
energy level diagram
.
Energy changes in an endothermic reaction
Sketch an
exothermic
energy level diagram in your books
Sketch an
exothermic
energy level diagram in your books

ammonium nitrate (s) ammonium ions (aq) + nitrate ions (aq)

water
Exothermic or Endothermic?
Answers
Sheldon's Revenge!
Safety
L8: Rate of Reaction
OCR 21st Century GCSE Sciene
The Practical
Why?
Copy and complete
Salts are used for k______ dialysis, fertilising s____ and in preserving f____.
Person 1:
Use the sheet to write a list of the equipment you will need for step 1.

Person 2:
Use the sheet to write a list of equipment you will need for step2
Person 2
Person 1
Measuring cylinder
Dilute sulfuric acid
250 cm3 beaker
Thermometer
Bunsen burner
Heat proof mat
Gauze
Tripod
Mass balance
A base (metal carbonate)
A spatula
A evaporating dish
Make sure someone is preparing for the next step

When heating, complete the method for synthesising a salt! (make sure the Bunsen is not near your paperwork!)
Heat (70oC) until the solution goes clear then add a little more carbonate until no more dissolves.
Add half a spatula of carbonate at a time, then stir until dissolved. Repeat until no more solid will dissolve and the solution turns slightly cloudy.
Warm (50oC) the sulfuric acid before adding the insoluble carbonate.
Sulfuric acid
Heat
the sulfuric acid
- this
increases the kinetic energy
of the acid particles and will
increase the rate of reaction
when the copper carbonate is added.
Use
copper carbonate
powder
- this has a
larger surface area
which will
increase the rate of reaction
.
Stir the solution -
this prevents it from bubbling up too much (safety precaution) when copper carbonate is added.
Add more copper carbonate little by little until no more dissolves
- the copper carbonate is in
excess
(
all the sulfuric acid reacts
).
Repeat this process until there is an excess of copper carbonate
Questions
6
2
4
5
1
3
1 litre of paint gas a cost of £24.
How much should 2.5 litres of paint cost?
1 litre covers 10 square metres
How much should 2.5 litres of paint cover?
4.54 litres costs £105.
How much area will this cover?
Is it a better deal than buying smaller pots separately?
Theoretical yield:
Because only 50 cm3 of H2SO4 was used divide the mass of product by 20 (
because1000/50 = 20
)

Theoretical mass of product = 160/20 = 8g of copper sulfate
Product
CuSO4
= 1 x Cu = 64
= 1 x S = 32
= 4 x O = 64
= 160 g
Reactant
H2SO4
= 2 x H = 2
= 1 x S = 32
= 4 x O = 64
= 98 g in 1000 cm3

Use H SO not CuCO for the calculation as the
CuCO was in excess

so not all of it was reacted
.
Percentage yield
=
actual yield
x 100
theoretical yield
L9: Synthesis of a Salt
L10: Reacting Masses & Yields
Percentage yield
Reacting masses - Theoretical yield
CuCO (s) + H SO (aq) CuSO (aq) + H O(l) + CO (g)
Filter mixture into an evaporating dish, to remove the excess solid
Heat the sulphuric acid until it starts to boil
Heat to evaporate the solution to 1/3 of its volume
(do not let it spit or boil dry)
Add copper carbonate and stir.
Return to the heat to speed up the reaction.
Heat the remaining solution over a water bath until dry crystals have formed
OR
Leave overnight to allow water to evaporate
Practical: Synthesis of a salt
Did you get them all?
Mass and Calculations
2
4
4
4
2
2
E.g
Joe made 12g of iron sulfide crystals.
He calculated that he should have made 20g.
Calculate his percentage yield.
Homework
Percentage yields sheet
Exam questions
You can start at Level 1 questions if you are confident at these type of questions
Try the sheet…
If you are confident in calculating formula mass start at the level 2 questions

If you need practice at working out formula mass start at the level 4 questions

Calculate the formula mass using the atomic mass’s from the periodic table.
Substitute the formula mass into an equation to calculate reacting masses.
Calculate the percentage yield.
REMEMBER TO DO THE SAME DIVISIONS AND MULTIPLICATIONS TO EVERYTHING
Calculating Theoretical Yield
magnesium+ sulfuric acid magnesium sulfate + hydrogen

Mg + H2SO4 MgSO4 + H2
2.5
litres
1
litres
0.75
litres
0.6
litres
£…
£?
£ 24
£…
£…
Scaling - How do you do it?
Paint example
4.54
litres
INFO:
The yield of the product you make can be calculated based on the proportions of chemicals you have used
Calculating reacting masses
REMEMBER TO
DO THE SAME
DIVISIONS AND MULTIPLICATIONS
TO EVERYTHING
x 105
÷ 4.54
4.54
litres
2.5
litres

1
litres
0.75
litres

0.6
litres

£105

£?

£…

£…

£…

What if it is a
difficult
number?
x 2.5
Learning Outcomes
x 2.5
How to synthesise (prepare) a solid salt
Copper carbonate
WHY?
WHY use powder?
WHY stir?
WHY?
Why does a mixture of magneisum carbonate and sulphuric acid froth up?
What is the advantage of:
using powdered magnesium carbonate?
warming when most of the acid has been used up?
adding a slight excess of the solid to the acid?
Going through the practical procedure for making a metal sulfate, identify the step when risks might arise from:
chemicals react vigorously and spill over
chemicals split and splash during heating
hot appratus that might cause burns
apparatus might crack and form sharp edges
Why is it important that the magneisum carbonate is added in excess to the sulfuric acid?
Carbon dioxide gas is produced in the reaction
Greater surface area - faster rate of reaction
Greater kinetic energy - faster rate of reaction
Make sure all the acid has reacted
When adding the carbonate to the acid
When evaporating the water from the sulfate solution
Bunsen burner, tripod, gauze, beaker, evap. dish
Transferring contents from beaker to evaporating dish
Make sure all the acid has reacted and the reaction is complete
Answers
1, 5, 3, 6, 4, 2
x 24
x 24
At the 4.54 litres price, how much would the other volume of paint cost?
13.88
57.82
23.12
17.34
Step 1:
Write down the balanced equation
Step 2:
Work out the relative formula mass of each reactant and product
Step 3:
Write the relative reacting masses under the balanced equation, taking into account the numbers used to balance the equation
Step 4:
Convert to reacting masses by adding the units (g, kg, or tonnes)
Step 5:
Scale the quantities to amounts actually used in the synthesis or experiment
Rules
Then work out the masses for:
Sulfuric acid
Magnesium sulfate
Hydrogen gas
Formula masses
To find the formula mass, we
add together the atomic masses for all the atoms
in the molecule.
Look at your periodic table. Read the key and then find the atomic mass for:
Magnesium
Hydrogen
Sulfur
Oxygen
If we started with 12g of magnesium, how much magnesium sulfate should we make?
3
2
3
3
What are the units we started with?
Let's apply our understanding
÷ 24
÷ 2
x 5
REMEMBER TO
DO THE SAME
DIVISIONS AND MULTIPLICATIONS
TO EVERYTHING
What Joe made was his
actual yield
;
he calculated his
theoretical yield
.
Substitute these values into the equation to calculate his
percentage yield
.
% yield = 12 x 100
20
= 0.6 x 100
= 60%
What was the theoretical yield from your synthesis of a salt?
Working
Synthesising a salt
Was this the most you could have made?

What percentage of the maximum did you make?
Weigh the copper sulfate made from last session.

What was its mass?
÷ 2
÷ 2
÷ 2
÷ 24
x 5
÷ 24
x 5
÷ 24
x 5
0.132
0.55
0.22
0.165
Full transcript