Organic chemistry
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Organic Chemistry. Structures. What do I need to know?. Translate between molecular, structural and ball and stick representations of simple organic molecules

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Organic Chemistry

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Organic chemistry

Organic Chemistry

Structures


What do i need to know

What do I need to know?

  • Translate between molecular, structural and ball and stick representations of simple organic molecules

  • Describe how the functional group affects the property of an organic compound and understand that alkanes are unreactive towards aqueous reagents because C—C and C—H bonds are unreactive;

  • Write balanced chemical reactions including for burning hydrocarbons including state symbols


Representations of organic molecules

Representations of organic molecules

  • There are a number of different ways to represent organic molecules.

  • Ball and stick – this is just like molymods


Representations of organic molecules1

Representations of organic molecules

  • Structural formula – this is where we show the covalent bonds between atoms as a line

  • Semi-structural (molecular) – this is where we write out the formula but do not include bonds; these are implied egCH3CH2OH


Organic chemistry

  • Molecular formula– this simply counts the numbers of each sort of atom present in the molecule, but tells you nothing about the way they are joined together.

  • EgC2H6O

  • This is the least helpful type of formula as it could be one of two (or more) different chemicals


Example question

Example question


Mark scheme

Mark scheme


Rules of organic molecules

Rules of organic molecules

Generally speaking

Carbon must make four bonds

Nitrogen must make three bonds

Oxygen must make two bonds

Hydrogen must make one bond

A double bond counts as two bonds eg C=C or C=O. A triple bond counts as three bonds.


Afl quiz

AfL - Quiz

  • Draw the structural formula for butanol

  • Write the molecular formula for butanol

  • Draw the structural formula for hexane

  • Write the molecular formula for hexane

  • Write the molecular formula for an alkane with 25 carbon atoms.

  • How many bonds does oxygen make in methanol?

    7. Give an example of a use for ethanol

    8. Give an example of a use for methanol


Organic chemistry

Butanol

C4H10O

Hexane

C6H14

C25H52

2

Fuel/feedstock for synthesis/solvent/used in perfume

Solvent, antifreeze, feedstock for adhesives and plastics


Understanding reactivity

Understanding reactivity

  • Alkanes are unreactive towards aqueous reagents because C-C and C-H bonds are unreactive.

  • What about organic molecules that have different bonds?

  • We call families of different types of bonded atoms FUNCTIONAL GROUPS

  • An example is the –OH group or alcohol group.


Different functional groups

Different functional groups


Alkanes and combustion

Alkanes and combustion

  • Because of the hydrocarbon chain alkanes burn readily releasing large amounts of energy.

  • Alkanes are therefore used as fuels.

  • When they burn completely they make carbon dioxide and water.

    eg octane (found in petrol)

    C8H18 +12 ½ O2 8CO2 + 9H2O


Example question1

Example question


Mark scheme1

Mark scheme


Example question2

Example question


Mark scheme2

Mark scheme


Balanced chemical equations

Balanced chemical equations

Write the balanced chemical equation for burning ethanol in air as a fuel and burning pentane as a fuel (include state symbols).


Answers

Answers

Ethanol

2C2H5OH(l) + 6O2(g)  4CO2(g) + 6H2O(l)

Pentane

C5H12(l)+ 8O2(g)  5CO2(g) + 6H2O (l)


Example questions

Example questions


Mark scheme3

Mark scheme


Alcohols and the manufacture of ethanol

Alcohols and the Manufacture of Ethanol

C7.1 and C7.5


What do i need to know1

What do I need to know?

1. The characteristic properties of alcohols are due to the presence of an –OH functional group

2. Know a range of methods for synthesising ethanol and limitations of fermentation reactions

3. Be able to explain why bioethanol is important for sustainability


Functional groups reminder

Functional groups - reminder

  • Look back at your table of functional groups.

  • Write a short paragraph to explain why different organic chemicals have different properties in terms of functional groups.

  • Use examples such as “carboxylic acids are acidic because they have a –COOH group”.


Can you recognise the functional group

Can you recognise the functional group?

  • Circle which of these are alcohols?


Answer

Answer

  • Alcohols have an –OH group


Properties and uses of alcohols

Properties and uses of alcohols

Properties:

  • volatile liquid (evaporates quickly at room temperature – more than water)

  • colourless

  • burns readily in air because of the hydrocarbon chain

  • good solvent


Example question3

Example question


Mark scheme4

Mark scheme


Uses of ethanol and methanol

Uses of ethanol and methanol

Ethanol: biofuels, solvents, feedstock for synthesis

Methanol: cleaner, feedstock for synthesis

Feedstock is the name we give to an “ingredient” on a chemical plant


Reactions of different functional groups

Reactions of different functional groups

  • This is illustrated very well by comparing the reaction of sodium with ethanol, hexane and water.

  • You have seen this reaction. Fill in the following table and compare with the mark scheme:


Observations with sodium

Observations with sodium


Mark scheme5

Mark scheme


Comparing functional groups

Comparing functional groups


Mark scheme6

Mark scheme


How do we make ethanol

How do we make ethanol?

  • Fermentation is a key process for obtaining ethanol. It is relatively cheap and requires wheat or beet sugar.

  • The process involves the anaerobic respiration of yeast at temperatures between 20 and 40°C and at pH 7.


Conditions for fermentation

Conditions for fermentation

Why is temperature important?

  • Outside an optimum temperature the yeast does not work (high temperatures kill the yeast).

    Why do you think pH is important?

  • Outside an optimum pH the yeast does not work (extremes of pH kill the yeast).

    Why do you think it is important to shut out oxygen?

  • To make ethanol the yeast must respire anaerobically (without oxygen).

    What effect will increasing ethanol concentration have on the yeast?

  • Eventually the ethanol concentration will be too high for the fermentation to continue. This means only a dilute solution can be made.


Example question4

Example question


Mark scheme7

Mark scheme


Example question5

Example question


Mark scheme8

Mark scheme


Example question6

Example question


Mark scheme9

Mark scheme


How do we obtain a concentrated solution

How do we obtain a concentrated solution?

  • Ethanol has a different boiling point to water. We can therefore separate water and ethanol using distillation.


Example question7

Example question


Mark scheme10

Mark scheme


Making ethanol using ethane from crude oil

Making ethanol using ethane from crude oil


Example question8

Example question


Mark scheme11

Mark scheme


Working out masses

Working out masses

  • We can use the useful relationship

  • Where Mr is the molecular mass

  • egMr of ethane C2H6 is (2 X 12) + (6 x 1) = 30


Example question9

Example question


Explanation

Explanation

  • In this question every ethene molecule that reacts makes one molecule of ethanol.

  • We need to relate the number of molecules to mass using our equation.

  • Mass 1 is mass of ethene = 1 tonne

  • Mr 1 is Mr of ethene = 28

  • Mass 2 is mass of ethanol = ?

  • Mr 2 is Mr of ethanol = 46


Mark scheme12

Mark scheme


Example question10

Example question


Mark scheme13

Mark scheme


Other alternatives

Other alternatives

  • Ethanol has also been synthesised using genetically modified e-coli bacteria and sugars from seaweed.

  • This process is sustainable as the seaweed and bacteria are renewable sources

  • Like yeast, bacteria can be killed by high concentrations of alcohol and high temperatures


Example question11

Example question


Mark scheme14

Mark scheme


Ethanol key facts

Ethanol – Key facts

  • Ethanol is made on an industrial scale as a fuel, a solvent and as a feedstock for other processes;

  • There is a limit to the concentration of ethanol solution that can be made by fermentation and there are optimum conditions of pH and temperature.

  • Ethanol solution can be concentrated by distillation to make products such as whisky and brandy;

  • Genetically modified E. coli bacteria can be used to convert waste biomass from a range of sources into ethanol and recall the optimum conditions for the process;

  • Ethane from crude oil can be converted into ethanol

  • Evaluating the sustainability of each process is important.


Bioethanol cycle

Bioethanol cycle


Balancing carbon cycle equations

Balancing carbon cycle equations

  • Glucose (a simple sugar) is created in the plant by photosynthesis.

  • Can you balance the following equation for photosynthesis?

    __CO2+ ___ H2O → C6H12O6 + __ O2

    6 CO2+ 6 H2O → C6H12O6 + 6 O2


Balancing carbon cycle equations1

Balancing carbon cycle equations

During ethanol fermentation, glucose is decomposed into ethanol and carbon dioxide.

Can you balance this equation?

C6H12O6→ __ CH3CH2OH+ __CO2

C6H12O6→ 2 CH3CH2OH+ 2 CO2


Balancing carbon cycle equations2

Balancing carbon cycle equations

During combustion ethanol reacts with oxygen to produce carbon dioxide, water, and heat:

Can you balance this equation?

CH3CH2OH + __ O2 → __ CO2 + __ H2O

CH3CH2OH + 3 O2 → 2 CO2 + 3 H2O


Carboxylic acids

Carboxylic acids

C7.1


What do i need to know2

What do I need to know?

  • understand that the properties of carboxylic acids are due to the presence of the –COOH functional group;

  • recall the names and formulae of methanoic and ethanoic acids;

  • recall that many carboxylic acids have unpleasant smells and tastes and are responsible for the smell of sweaty socks and the taste of rancid butter;

  • understand that carboxylic acids show the characteristic reactions of acids with metals, alkalis and carbonates;

  • recall that vinegar is a dilute solution of ethanoic acid.


Can you recognise the functional group1

Can you recognise the functional group?

  • Circle which of these is a carboxylic acid?


Answer1

Answer

  • This is a carboxylic acid


Methanoic and ethanoic

Methanoic and Ethanoic

Methanoic acid

Ethanoic acid (VINEGAR)


Acids in nature

Acids in nature

Many acids are part of life itself, they are known as CARBOXYLIC acids

Organic or CARBOXYLIC acids are part of life itself and can be found in many animals and plants.


Reactions of carboxylic acids

Reactions of carboxylic acids

Reaction of carboxylic acids

1) Acid + metal  salt + hydrogen

Ethanoic acid + magnesium  magnesium ethanoate + hydrogen

2) Acid + metal oxide  salt + water

Ethanoic acid + copper oxide  copper ethanoate + water

3) Acid + metal carbonate  salt + water + carbon dioxide

Ethanoic acid + sodium carbonate  sodium ethanoate + water + carbon dioxide


Example question12

Example Question


Mark scheme15

Mark scheme


Example question13

Example question


Mark scheme16

Mark scheme


Example question14

Example question


Mark scheme17

Mark scheme


Esters fats and oils

Esters, Fats and Oils

C7.1


What do i need to know3

What do I need to know?

1. Recall the method for producing an ester using reflux

2. Describe how fats and oils are all types of ester and explain how margarine is made

3. Explain how bromine water can be used to test whether a fat is saturated or unsaturated.


Making esters

Making esters

What type of organic chemicals do you need to mix together?

Can you name the ester made from ethanoic acid and methanol?


Making esters1

Making esters

What type of organic chemicals do you need to mix together?

  • A carboxylic acid and an alcohol with an acid catalyst

    Can you name the ester made from ethanoic acid and methanol?

  • Methyl ethanoate


Esters

Esters


Example question15

Example question


Mark scheme18

Mark scheme


Making esters2

Making esters


Reflux apparatus

Reflux apparatus


How do i describe reflux for an exam

How do I describe reflux for an exam?

  • Mixture heated in flask (1) …

  • with condenser above (1) …

  • so no liquid is lost by evaporation and allows longer time for the reaction (1)


Distillation

Distillation


Describing distillation

Describing distillation

  • The mixture is heated

  • At the boiling point of the ester is becomes a vapour

  • The vapour is condensed in the condenser

  • The liquid is collected


Purification

Purification

  • Collected ester is shaken in a separating funnel with distilled water.

  • Impurities dissolve in the water

  • Impurities are tapped off

Ester


Drying

Drying

  • Solid drying agent is added to the product

  • This could be calcium chloride or sodium sulphate

  • This removes water from the product


Example question16

Example question


Mark scheme19

Mark scheme


Example question17

Example question


Mark scheme20

Mark scheme


Example question18

Example question


Mark scheme21

Mark scheme


Fats and oils

Fats and oils

  • These are a special type of ester made from glycerol and fatty acids.


Fats and oils1

Fats and oils

  • Removal of water in the condensation reaction makes a fat or oil


Saturated or unsaturated

Saturated or unsaturated?

  • Have you heard these terms on the television?

  • Vegetable oil is mostly unsaturated

  • Animal fat is mostly saturated


Double bonds or not

Double bonds or not

  • A saturated fat has no C=C double bonds (alkene functional groups) and is usually a solid fat like margarine or animal fat.

  • An unsaturated fat has C=C double bonds and is usually an oil like vegetable oil.


Example question19

Example question


Mark scheme22

Mark scheme


Making margarine

Making margarine

  • To make margarine we have to saturate vegetable oil by bubbling hydrogen gas through the oil.

  • This process is called hydrogenation


Is a fat or oil saturated or not

Is a fat or oil saturated or not?

  • We can test for this by adding bromine water.

  • If there are double bonds present the bromine water changes from orange/brown to colourless.


Example question20

Example question


Mark scheme23

Mark scheme


Hydrolysis

Hydrolysis

  • When an ester is hydrolysed it goes back to an acid and alcohol

  • We can hydrolyse by adding acid or alkali (NaOH).


Example question21

Example question


Mark scheme24

Mark scheme


Energy changes in chemistry

Energy changes in chemistry

C7.2


Organic chemistry

Quiz

  • When a chemical reaction takes place heat may be given out or taken in.

  • Can you remember the word we use when heat is given out?

  • Can you remember the word we use when heat is taken in?


What do i need to know4

What do I need to know?

  • Recall and use the terms ENDOTHERMIC and EXOTHERMIC

  • Describe examples of ENDOTHERMIC and EXOTHERMIC reactions.

  • Use simple energy level diagrams to represent ENDOTHERMIC and EXOTHERMIC reactions.


Change in energy

Change in energy

  • Chemical reactants have a certain amount of chemical energy stored within them.

  • When the reaction has taken place they have either more or less energy stored within them than before.


Definitions

Definitions

When heat is given out (exothermic) then the products have less energy than they did before. They have lost it to the surroundings.

When heat is taken in (endothermic) then the products have more energy than they had before. They have taken it from the surroundings.


Energy level diagrams

Energy level diagrams

Which diagram do you think is endothermic and which is exothermic?

Heat given out

Heat taken in


Energy level diagrams1

Energy level diagrams

EndothermicExothermic

Heat given out

Heat taken in

Energy level of products is higher than reactants so heat taken in.

Energy level of products is lower than reactants so heat given out.


Example question22

Example question


Mark scheme25

Mark scheme


Bond enthalpies

Bond enthalpies

C7.2


Quick quiz

Quick quiz

  • Reactions where the products are at a lower energy than the reactants are endothermic (TRUE/FALSE)

  • Activation energy is the amount of energy given out when a reaction takes place (TRUE/FALSE)

  • A reaction which is exothermic transfers heat energy to the surroundings (TRUE/FALSE)

  • How can we tell if a reaction is exothermic or endothermic?

  • Sketch the energy profile for an endothermic reaction.

  • When methane (CH4) burns in oxygen (O2) bonds between which atoms need to be broken?


Answers1

Answers

  • Reactions where the products are at a lower energy than the reactants are endothermic (TRUE/FALSE)

  • Activation energy is the amount of energy given out when a reaction takes place (TRUE/FALSE)

  • A reaction which is exothermic transfers heat energy to the surroundings (TRUE/FALSE)

  • How can we tell if a reaction is exothermic or endothermic?

  • Sketch the energy profile for an endothermic reaction.

  • When methane (CH4) burns in oxygen (O2) bonds between which atoms need to be broken?

FALSE

FALSE

TRUE

Measure the temperature change

C—H bonds and O=O bonds


What do i need to know5

What do I need to know?

1. Recall that energy is needed to break chemical bonds and energy is given out when chemical bonds form

2. Identify which bonds are broken and which are made when a chemical reaction takes place.

3. Use data on the energy needed to break covalent bonds to estimate the overall energy change for a reaction.


Activation energy revisited

Activation energy revisited

  • What is the activation energy of a reaction?

  • The energy needed to start a reaction.

  • BUT what is that energy used for and why does the reaction need it if energy is given out overall?

  • The activation energy is used to break bonds so that the reaction can take place.


Burning methane

Burning methane

Consider the example of burning methane gas.

CH4 + 2O2 CO2 + 2H2O

This reaction is highly exothermic, it is the reaction that gives us the Bunsen flame. However mixing air (oxygen) with methane is not enough. I need to add energy (a flame).


What happens when the reaction gets the activation energy

What happens when the reaction gets the activation energy?

C

H

H

H

H

O

O

O

O

Bond

Breaking

Bond

Forming

H

O

O

Energy in chemicals

C

O

O

O

H

H

H

H

H

O

C

O

O

H

H

Progress of reaction


Using bond enthalpies

Using bond enthalpies

By using the energy that it takes to break/make a particular bond we can work out the overall enthalpy/energy change for the reaction.

Sum (bonds broken) – Sum (bonds made) = Energy change


Bin mix

BIN MIX

Breaking bonds is ENDOTHERMIC energy is TAKEN IN when bonds are broken

Making bonds is EXOTHERMIC energy is GIVEN OUT when bonds are made.


Bond enthalpies1

Bond enthalpies


Can you work out the energy change for this reaction

Can you work out the energy change for this reaction?

CH4 + Cl2 CH3Cl + HCl

Tip: Draw the reactants and products and work out the bonds you are breaking and the ones you are making.


The answer is 120 kj

The answer is -120 kJ


Example question part 1

Example question part 1


Question part 2

Question part 2


Question part 3

Question part 3


Mark scheme26

Mark scheme


Challenge question

Challenge question

  • The true value for the energy change is often slightly different from the value calculated using bond enthalpies.

  • Why do you think this is?


Example question23

Example question

The calculated value is 120 kJ


Mark scheme27

Mark scheme


Definitions1

Definitions

Write each of these phrases in your book with a definition in your own words:

  • Exothermic reaction

  • Endothermic reaction

  • Activation energy

  • Catalyst

  • Bond energy/enthalpy


How did you do

How did you do?

Exothermic reaction

A reaction which gives energy out to the surroundings.

Endothermic reaction

A reaction which takes in energy from the surroundings.

Activation energy

The energy required to start a reaction by breaking bonds in the reactants

Catalyst

A substance that increases the rate of a reaction by providing an alternative pathway with lower activation energy. It is not used up in the process of the reaction

Bond energy/enthalpy

The energy required to break a certain type of bond. The negative value is the energy given out when that bond is made.


Popular exam question

Popular exam question

  • Explain why a reaction is either exothermic or endothermic?

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Popular exam question1

Popular exam question

  • Explain why a reaction is either exothermic or endothermic?

    • In a chemical reactions some bonds are broken and some bonds are made.

    • Breaking bonds takes in energy.

    • Making bonds gives out energy.

    • If the energy given out making bonds is higher than the energy needed to break them the reaction is exothermic.

    • If the energy needed to break bonds is higher than the energy given out making them the reaction is endothermic.


Chemical equilibria

Chemical Equilibria

C7.3 Reversible Reactions & Dynamic Equilibria


What do i need to know6

What do I need to know?

  • State that some chemical reactions are reversible

  • Describe how reversible reactions reach a state of equilibrium

  • Explain this using dynamic equilibrium model.


Reversible or not reversible

Reversible or not reversible

Until now, we were careful to say that most chemical reactions were not reversible –

They could not go back to the reactants once the products are formed.


Example

Example

In the case of the vast majority of chemical reactions this is true, the reaction of methane and oxygen for example:

CH4(g) + O2(g)   CO2(g) + 2H2O(l)

It is almost impossible to return the carbon dioxide and water to the original methane and oxygen.


Reversible

Reversible

  • Some chemical reactions, however, will go backwards and forwards depending on the conditions.

  • CoCl2·6H2O(s)  CoCl2(s) + 6H2O(l)

    pinkblue


How do we write them down

How do we write them down?

  • This is the symbol for used for reversible reactions.

    CoCl2·6H2O(s) CoCl2(s) + 6H2O(l)


What is equilibrium

What is equilibrium?

  • Reversible reactions reach a balance point, where the amount of reactants and the amount of products formed remains constant.

  • This is called a position of equilibrium.


Dynamic equilibrium

Dynamic Equilibrium.

  • In dynamic equilibrium the forward and backwards reactions continue at equal rates so the concentrations of reactants and products do not change.

  • On a molecular scale there is continuous change.

  • On the macroscopic scale nothing appears to be happening. The system needs to be closed – isolated from the outside world.


Example question24

Example question


Mark scheme28

Mark scheme


Dynamic equilibria

Dynamic Equilibria

C7.3 Controlling equilibria


What do i need to know7

What do I need to know?

1. Recall that reversible reactions reach a state of dynamic equilibrium.

2.Describe how dynamic equilibria can be affected by adding or removing products and reactants.

3. Explain the difference between a “strong” and “weak” acid in terms of equilibria


Position of the equilibrium

Position of the equilibrium

  • Equilibrium can “lie” to the left or right.

  • This is “in favour of products” or “in favour of reactants”

  • Meaning that once equilibrium has been reached there could be more products or more reactants in the reaction vessel.


Le chatelier s principle

Le Chatelier’s principle

  • If you remove product as it is made then equilibrium will move to the right to counteract the change

  • If you add more reactant then equilibrium will move to the right to counteract the change.

  • In industry we recycle reactants back in and remove product as it is made to push the equilibrium in favour of more product.


Complete

Complete

When a system is at__________ to make more product you can_________ product or add more __________ for example by recycling them back in.

To return to reactants you ______ product or remove_________.

[equilibrium, add, reactant, remove, product]


Strong and weak acids

Strong and weak acids

A strong acid is one which is FULLY IONISED in water. It will have a high hydrogen ion concentration

HCl H+ + Cl-

A weak acid is one which is NOT fully ionised and is in equilibrium. It has a low hydrogen ion concentration

CH3COOH CH3COO- + H+

Caution – weak and strong are not the same as concentration.


Mark scheme29

Mark scheme


Example question25

Example question


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Mark scheme


Practicing definitions

Practicing definitions

Write each of these phrases in your book with a definition in your own words:

  • Reversible reaction

  • Dynamic equilibrium

  • Position of equilibrium

  • Strong acid

  • Weak acid


How did you do1

How did you do?

Reversible reaction

A reaction that can proceed in the forward or reverse directions (represented by two arrows in an equation).

Dynamic equilibrium

The point where the rate of the forward reaction = rate of the reverse reaction.

Position of equilibrium

The point where there is no further change in the concentration of either reactants or products. The position can lie to the left (favouring reactants) or right (favouring products).

Strong acid

An acid that is completely dissociated in water

Weak acid

An acid that is only partly dissociated in water because the reaction is in dynamic equilibrium and favours the reactants (LHS).


Popular exam question2

Popular exam question

  • Ethanoic acid (CH3COOH) is a weak acid but hydrochloric acid is a strong acid. Use ideas about ion formation and dynamic equilibrium to explain this difference.

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Popular exam question3

Popular exam question

Ethanoic acid (CH3COOH) is a weak acid but hydrochloric acid is a strong acid. Use ideas about ion formation and dynamic equilibrium to explain this difference.

  • Hydrochloric acid ionises completely

  • So hydrogen ion concentration is high

  • Ethanoic acid only partly dissociates because the reaction is reversible

  • Equilibrium is mainly to the left

  • So hydrogen ion concentration is low.


Analysis

Analysis

C7.4 – Analytical Procedures


What do i need to know8

What do I need to know?

1. Recall the difference between qualitative and quantitative methods of analysis.

2. Describe how analysis must be carried out on a sample that represents the bulk of the material under test

3. Explain why we need standard procedures for the collection, storage and preparation of samples for analysis


Qualitative vs quantitative

Qualitative vs. Quantitative

  • A qualitative test is usually very quick. It can give vital information without needing to wait too long for it.

  • A quantitative test gives precise values, for example for a concentration in Moldm-3

  • Examples of qualitative tests include universal indicator, silver nitrate for halide ions and bromine water for unsaturation.

  • Examples of quantitative tests include titration, chromatography and spectroscopy.


Which sample should i test

Which sample should I test?

  • It is important that the sample represents the bulk of the material under test.

  • You may chose to test more than one sample from a range of points to ensure that you have results which represent the whole.

  • For example is it well mixed? Are their pockets of higher concentration/different composition?


Chemical industry

Chemical industry

  • Analysis of samples is crucial to the chemical industry to ensure the quality of the chemicals they are manufacturing. Some are analysed numerous times a day or even within an hour.

  • To maintain consistency it is essential that we use standard procedures to:

    • collect the sample

    • store the sample

    • prepare the sample for analysis

    • analyse the sample.


Chromatography

Chromatography

C7.4 – paper chromatography


Chromatography1

Chromatography


Solvents

Solvents

  • The mobile phase is the solvent – the part that moves

    2. In paper chromatography it is water or ethanol


Paper column

Paper/column

  • The stationary phase is the paper in paper chromatography or the column in gas chromatography.

  • In thin layer chromatography it is silica gel on a glass plate

  • The stationary phase does not move.


How does the technique work

How does the technique work?

In chromatography, substances are separated by movement of a mobile phase through a stationary phase.

Each component in a mixture will prefer either the mobile phase OR the stationary phase.

The component will be in dynamic equilibrium between the stationary phase and the mobile phase.


Substance a

Substance A

  • This is substance A

  • Substance A prefers the stationary phase and doesn’t move far up the paper/column.

  • The equilibrium lies in favour of the stationary phase.


Substance b

Substance B

  • This is substance B

  • Substance B prefers the mobile phase and moves a long way up the paper/column

  • The equilibrium lies in favour of the mobile phase


Using a reference

Using a reference

  • In chromatography we can sometimes use a known substance to measure other substances against.

  • This will travel a known distance compared to the solvent and is known as a standard reference.


Advantages of tlc

Advantages of TLC

TLC has a number of advantages over paper chromatography.

It is a more uniform surface chromotograms are neater and easier to interpret

Solvent can be used which is useful if a substance is insoluble in water.


Past paper questions

Past Paper Questions


Past paper question

Past paper question


Mark scheme31

Mark scheme


Describing how chromatography works exam definition

Describing how chromatography works – exam definition

  • stationary phase is paper and mobile phase is solvent / mobile phase moves up through stationary phase (1)

  • for each compound there is a dynamic equilibrium between the two phases (1)

  • how far each compound moves depends on its distribution between the two phases (1)


Using an r f value

Using an Rf value

  • In order to be more precise we can use measurements on the TLC plate to compare the distance travelled by our substance (the solute) with the distance travelled by the solvent.

  • The Rf value is constant for a particular compound.

  • The distance travelled however could be different on different chromatograms.

  • The Rf value is always less than 1.


Rf value

Rf value


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Example question

This question relates to the chromatogram shown in the earlier question. Refer back…


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Example question27

Example question


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Past paper question1

Past paper question


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Gas liquid chromatography

Gas-liquid chromatography

C7.4 GLC


What do i need to know9

What do I need to know?

  • recall in outline the procedure for separating a mixture by gas chromatography (gc);

  • understand the term retention time as applied to gc;

  • interpret print-outs from gc analyses.


Gas chromatography

Gas chromatography

  • The mobile phase is an unreactive gas known as the carrier gas this is usually nitrogen

  • The stationary phase is held inside a long column and is lots of pieces of inert solid coated in high bp liquid.

  • The column is coiled in an oven

  • The sample to be analysed is injected into the carrier gas stream at the start of the column.


Organic chemistry

GC


Gc analysis

GC analysis

  • Each component of the sample mixture has a different affinity for the stationary phase compared with the mobile phase

  • Therefore each component travels through the column in a different time.

  • Compounds favouring the mobile phase (usually more volatile) emerge first.

  • A detector monitors the compounds coming out of the column and a recorder plots the signal as a chromatogram


Glc chromatograph

GLC Chromatograph


Interpretation

Interpretation

  • The time in the column is called the retention time

  • Retention times are characteristic so can identify a compound

  • Area under peak or relative heights can be used to work out relative amounts of substances


The key points revise this

The key points – revise this!

  • the mobile phase carries the sample (1)

  • components are differently attracted to the stationary and mobile phases (1)

  • the components that are more strongly attracted to the stationary phase move more slowly (1)

  • the amount of each component in the stationary phase and in the mobile phase is determined by a dynamic equilibrium (1)


Past paper question2

Past paper question


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Titration

Titration

C7.4


What do i need to know10

What do I need to know?

  • Calculate the concentration of a given volume of solution given the mass of solvent;

  • Calculate the mass of solute in a given volume of solution with a specified concentration;

  • Use the balanced equation and relative formula-masses to interpret the results of a titration;


Concentration

Concentration

  • We can measure the concentration of solution in grams/litre. This is the same as g/dm3

  • 1dm3 = 1000cm3

  • If I want to make a solution of 17 g/dm3 how much will I dissolve in 1dm3.

  • 17 g

  • If I want to make a solution of 17g/dm3 but I only want to make 100cm3 of it how much will I dissolve?

  • 1.7g


Making standard solutions

Making standard solutions

  • For a solution of 17g/dm3

  • First I will measure 17g of solid on an electronic balance


Making standard solutions1

Making standard solutions

  • Now I must dissolve it in a known 1dm3 of water.

  • I transfer it to a volumetric flask and fill up with distilled water to about half the flask.

  • I then swirl to dissolve

  • Top up with a dropping pipette so that the meniscus is on the line.


How much to dissolve

How much to dissolve?

  • Worked example:

  • I want to make 250cm3 of a solution of 100g/dm3.

  • How much solid do I transfer to my 250cm3 volumetric flask?


How much to dissolve1

How much to dissolve?

Worked example:

I want to make 250cm3 of a solution of 100g/dm3.

1. Work out the ratio of 250cm3 to 1000cm3

250/1000 = 0.25

2. I therefore need 0.25 of 100g in 250cm3 which is 0.25x100=25g


General rule

General rule


Practie how much to dissolve

Practie - how much to dissolve?

  • I want to make 250cm3 of a solution of 63.5g/dm3.

  • How much solid do I transfer to my 250cm3 volumetric flask?

  • 250/1000 x 63.5 = 15.9 g


Practice how much to dissolve

Practice - how much to dissolve?

  • I want to make 100cm3 of a solution of 63.5g/dm3.

  • How much solid do I transfer to my 100cm3 volumetric flask?

  • 100/1000 x 63.5 = 6.35 g


Concentration from mass and volume

Concentration from mass and volume

We need to rearrange this:

To give


What is the concentration of

What is the concentration of?

  • 12g dissolved in 50cm3

  • 50g dissolved in 100cm3

  • 47g dissolved in 1000cm3

  • 200g dissolved in 250cm3


What is the concentration of1

What is the concentration of?

  • 12g dissolved in 50cm3

    = 1000/50 x 12

    = 240g/dm3

  • 50g dissolved in 100cm3

    =1000/100 x 50

    = 500g/dm3

  • 47g dissolved in 1000cm3

    = 1000/1000 x 47

    = 47g/dm3

  • 200g dissolved in 250cm3

    1000/250 x 200

    = 800g/dm3


Solutions from stock solutions

Solutions from stock solutions


Making solutions from stock solutions

Making solutions from stock solutions

If I have a solution containing 63g/dm3, how do I make up 250cm3 of a solution of concentration 6.3g/dm3?

To make 1dm3 of 6.3g/dm3 I would need 100cm3

To make 250cm3 of 6.3g/dm3I would therefore need 25cm3 and make it up to 250cm3 with distilled water


Working out masses1

Working out masses

  • We can use the useful relationship

  • Where Mr is the molecular mass

  • egMr of NaOH is (23 + 16 + 1) = 40

  • This can help us to calculate an unknown mass


Titration calculations

Titration calculations

  • In a titration we have added a known amount of one substance usually an acid (in the burette) to a known amount of another substance usually an alkali (in the conical flask).

  • The amount added allows us to determine the concentration of the unknown.


Titration equipment

Titration equipment


Using a table

Using a table

  • It can be helpful to sketch a table to keep track of information you know…


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Uncertainty

Uncertainty

  • Uncertainty is a quantification of the doubt about the measurement result.

  • In a titration the uncertainty is the range of the results.

  • If results are reliable then it will be within 0.2cm3

  • NOTE THAT THIS IS RELIABLE NOT NECESSARILY ACCURATE


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C7 5 green chemistry

C7.5 Green Chemistry

The Chemical Industry


What do i need to know11

What do I need to know?

  • Recalland use the terms 'bulk' (made on a large scale) and 'fine' (made on a small scale) in terms of the chemical industry with examples;

  • Describe how new chemical products or processes are the result of an extensive programme of research and development;

  • Explain the need for strict regulations that control chemical processes, storage and transport.


Bulk processes

Bulk processes

  • A bulk process manufactures large quantities of relatively simple chemicals often used as feedstocks (ingredients) for other processes.

  • Examples include ammonia, sulfuric acid, sodium hydroxideand phosphoric acid.

  • 40 million tonnes of H2SO4 are made in the US every year.


Fine processes

Fine processes

  • Fine processes manufacture smaller quantities of much more complex chemicals including pharmaceuticals, dyes and agrochemicals.

  • Examples include drugs, food additivesand fragrances

  • 35 thousand tonnes of paracetamol are made in the US every year.


Example question28

Example question


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Research and development

Research and Development

  • All chemicals are produced following an extensive period of research and development.

  • Chemicals made in the laboratory need to be “scaled up” to be manufactured on the plant.


Research in the lab

Research in the lab


Examples of making a process viable

Examples of making a process viable

  • Trying to find suitable conditions – compromise between rate and equilibrium

  • Trying to find a suitable catalyst – increases rate and cost effective as not used up in the process.


Catalysts

Catalysts

  • Can you give a definition of a catalyst?

  • A substance which speeds up the rate of a chemical reaction by providing an alternative reaction pathway.

  • The catalyst is not used up in the process

  • Catalysts can control the substance formed eg Ziegler Natta catalysts.


Regulation of the chemical industry

Regulation of the chemical industry

  • Governments have strict regulations to control chemical processes

  • Storage and transport of chemicals requires licenses and strict protocol.

  • Why?

  • To protect people and the environment.


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Example question


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Process development

Process development


Example question part 11

Example question – part 1


Example question part 2

Example question part - 2


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Example question part 3

Example question – part 3


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Factors affecting the sustainability of a process

Factors affecting the sustainability of a process


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Example question


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Atom economy

Atom economy


Atom economy calculation

Atom economy calculation

For example, what is the atom economy for making hydrogen by reacting coal with steam?

Write the balanced equation:

C(s) + 2H2O(g) → CO2(g) + 2H2(g)

Write out the Mr values underneath:

C(s) + 2H2O(g) → CO2(g) + 2H2(g)

12 2 × 18 44 2 × 2

Total mass of reactants 12 + 36 = 48g

Mass of desired product (H2) = 4g

% atom economy = 4⁄48 × 100 = 8.3%


Organic chemistry

Example question


Example question part 21

Example question – part 2


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