18 replies to this topic

[linds]

We got a sheet out before the end of term with all the possible PPA questions on it. And since I'm such a nice girl, I thought I'd type them out or you all.

You're always going to get a question on one of the PPA's, so if you know the answers to these then you're, to quote my Maths teacher, flying by the seat of your pants. Or something.

Unit 1

PPA1 - the effect of concentration changes on reaciton rate

Aim: The aim is to find the effect of varying the concentration of iodide ions on the rate of reaction between hydrogen peroxide and acidified potassium iodide solution.

a) Suggest a method for measuring the rate of this reaction
b) The experiment was carried out to investigate the effect of iodide ion concentration on reaction rate.  Suggest two factors which should be kept constant throughout the experiment.
c) How is the course of reaction followed?
d) Suggest any safety precautions which should be carried out.


PPA2 - the effect of temperature changes on reaction rate

Aim: The aim is to find the effect of varying temperature on the rate of reaction between oxalic acid and an acidified solution of potassium permanganate.

a) Suggest an experiment to investigate the effect of temperature on the reaction rate - can you name the acid used?
b) Suggest two factors which should be kept constant throughout the experiment.
c) How is the course of the reaction followed?
d) What are the units of reaction rate?
e) Suggest any safety precautions which should be carried out.


PPA3 - The Enthalpy of Combustion

Aim: The aim is to determine the enthalpy of combustion of ethanol.

a) Draw a diagram of the apparatus you would use
b) List all the safety precautions you should take
c) The experimental value is often much less than the data book value.  Give two reasons for this, including one which is not related to heat loss to the surroundings.



Unit 2

PPA 1 - Oxidation

Aim: The aim is to use the mild oxidising agents (acidified potassium dichromate solution, Benedict's solution and Tollen's reagent) to distinguish between two given carbonyl compounds, one of which is an aldehyde, the other a ketone.

a) Name suitable oxidising agents and be able to give the colour change involved when they react.
b) Why is the potassium dichromate acidified?
c) List all the safety precautions you should take


PPA2 - making esters

Aim: The aim is to prepare and ester and identify some of the characteristic properties of esters.

a) Describe the function of the sulphuric acid.
b) Draw a diagram to show how you would heat the mixture
c) Mention any necessary safety precautions
d) Describe how you would detect the presence of an ester
e) It was stated that some of the reaction mixture would be lost through evaporation during heating.  Make an addition to your diagram to show how this could be reduced.


PPA3 - Factors affecting enzyme activity

Aim: The aim is to investigate the effect of pH or temperature changes on enzyme activity.

a) Suggest a method for measuring enzyme activity of an enzyme under conditions of varied pH or temperature.
b) What measurements would you take?
c) What form would the resulting graph of pH/temperature against enzyme activity take?



Unit 3

PPA1 - Hess's Law

Aim : The aim of the experiment is to confirm Hess's law.

a) What measurements must be taken at each stage?
b) Explain why a plastic beaker is preferable to a metal one.
c) List any safety precautions you would take.
d) Before adding together the solutions of acid and alkali, how is the initial temperature determined?


PPA2 - Quantative Electrolysis

Aim: The aim is to confirm the reaction 2H+(aq) + 2e ----> H2(g), that is to determine the quantity of electricity required to produce one mole of hydrogen by electrolysing dilute sulphuric acid.

a) Draw a diagram of the apparatus used.
b) In order to find the quantity of electricity in order to produce one mole of hydrogen by electrolysis, what measurements have to be made?
c) List any safety precautions you would take.


PPA3 - A Redox Titration

Aim: The aim is to determine the mass of vitamin C in a tablet by carrying out a redox titration using a solution of iodine of accurately known concentration and starch solution as an indicator.

a) What is meant by a standard solution and how can one be prepared?
b) How could the end point of the titration be determined?
c) List an apparatus needed for such a titration.
d) From the results of several titrations, including a rough one, what volume of solution would be used in the calculation?

CLICK HERE FOR ANSWERS

Edited by Ally, 29 January 2006 - 05:48 PM.

[Laura]

That's really good, my chemistry teacher didn't give us anything like that!

Do you also have the answers to these questions? Have scrolled through the list and can answer most of them except:

Unit 2 PPA 1 - Oxidation

Why is the potassium dichromate acidified?

and, Unit 3 PPA 1 - Hess's Law

Explain why a plastic beaker is preferable to a metal one


The answers are probably really simple lol but would appreciate it if anyone could explain.

Thanks, Laura

[George]

I'm not sure about the first one Laura, but off the top of my head it might be because H+ ions are involved in a redox reaction.

For the Hess's Law PPA, a plastic beaker is used as it is a good insulator; this means the reaction does not lose as much energy to the surroundings.

Hope that helps!

[Discogirl17]

Yep George is write about the question why is it acidified?

The answer is indeed exactly what he said. Acid contains an H+ ions which are used in the oxidation process.

[Laura]

Thanks makes a whole lot more sense now!

[Pyxelle]

[quote=Lindsay,May 31 2004, 06:03 PM]
You're always going to get a question on one of the PPA's, so if you know the answers to these then you're, to quote my Maths teacher, flying by the seat of your pants. Or something. [end quote]

I hear tell there is going to be a question on at least one PPA for each unit (1, 2 and 3), or possibly two. There will be six marks in total awarded for PPAs , with 2 marks in each unit- is this making any sense?
Unit 1: PPA question(s) worth 2 marks
Unit 2: PPA question(s) worth 2 marks
Unit 3: PPA question(s) worth 2 marks

Six marks in total.

So Lindsay's right: know your PPA stuff and you're off to a good start...

I need to revise!

[bred]

Much appreciated Lindsay (I only found this thread now)!

[gary]

Any chance of posting all the answers if you have the chance?

[cat]

All the answers to PPAs are on this website- I just printed them out. Unfortunately I've already done Unit 2 PPAs!

[gary]

PPA2 - making esters


e) It was stated that some of the reaction mixture would be lost through evaporation during heating. Make an addition to your diagram to show how this could be reduced.

What would I add to my diagram.

[Ally]

You'd add a wet paper towel.

Here are the Unit 2 PPA notes.

[bred]

PPA Answers

Unit 1

PPA1 - the effect of concentration changes on reaction rate

Aim: The aim is to find the effect of varying the concentration of iodide ions on the rate of reaction between hydrogen peroxide and acidified potassium iodide solution.

a) Suggest a method for measuring the rate of this reaction

Since the amount of thiosulphate ions initially present will be the same in each experiment, the appearance of the blue/black colour will always represent the same extent of reaction. So if t is the time it takes for the blue/black colour to appear then we can take 1/t as a measure of the reaction rate.

b) The experiment was carried out to investigate the effect of iodide ion concentration on reaction rate. Suggest two factors which should be kept constant throughout the experiment.


1. The concentration of hydrogen peroxide
2. The temperature at which the experiments are performed.

c) How is the course of reaction followed?

The course of this reaction can be followed by carrying it out in the presence of small quantities of starch and sodium thiosulphate solutions.

d) Suggest any safety precautions which should be carried out.


1. Safety glasses should be worn as both 1 mol l-1 sulphuric acid and 0. 1 mol l-1 hydrogen peroxide irritate the eyes.
2. Syringes should be pointed downwards to prevent inury.

PPA2 - the effect of temperature changes on reaction rate

Aim: The aim is to find the effect of varying temperature on the rate of reaction between oxalic acid and an acidified solution of potassium permanganate.

a) Suggest an experiment to investigate the effect of temperature on the reaction rate - can you name the acid used?

Oxalic acid.

b) Suggest two factors which should be kept constant throughout the experiment.

The concentrations and volumes of the reactants.

c) How is the course of the reaction followed?

Initially the reaction mixture is purple in colour due to the presence of the permanganate ions but it will turn colourless as soon as they are used up.

d) What are the units of reaction rate?

s-1

e) Suggest any safety precautions which should be carried out.


1. Safety glasses should be worn as both 1 mol l-1 sulphuric acid and 0.1 mol l-1 hydrogen peroxide irritate the eyes.
2. Syringes should be pointed downwards to prevent inury.

PPA3 - The Enthalpy of Combustion

Aim: The aim is to determine the enthalpy of combustion of ethanol.

a) Draw a diagram of the apparatus you would use



b) List all the safety precautions you should take


1. Safety glasses hould be worn.
2. Experiment apparatus should be kept well away from other flammable substances.

c) The experimental value is often much less than the data book value. Give two reasons for this, including one which is not related to heat loss to the surroundings.


1. Heat was lost to the surroundings.
2. Incomplete combustion of ethanol.

Unit 2

PPA 1 - Oxidation

Aim: The aim is to use the mild oxidising agents (acidified potassium dichromate solution, Benedict's solution and Tollen's reagent) to distinguish between two given carbonyl compounds, one of which is an aldehyde, the other a ketone.

a) Name suitable oxidising agents and be able to give the colour change involved when they react.


With aldehydes:
Tollen's reagent gives a silver mirror effect on the side of the test tube.
With Fehling's solution the blue colour transforms into a dark red precipitate of copper (I) oxide.
With ketones:
There is no change.

b) Why is the potassium dichromate acidified?

To increase the number of H+ ions

c) List all the safety precautions you should take


1. Safety glasses should be worn
2. Gloves should be worn to handle Tollen's reagent and the carbonyl compounds.

PPA2 - making esters

Aim: The aim is to prepare an ester and identify some of the characteristic properties of esters.

a) Describe the function of the sulphuric acid.

Sulphuric acid performs as a strong oxidising agent.

b) Draw a diagram to show how you would heat the mixture



c) Mention any necessary safety precautions

Safety goggles should be worn.

d) Describe how you would detect the presence of an ester


1. There should be an oily layer on the top of the reaction mixture if an ester is present.
2. The ester should also give off a pleasant smell, similar to that of fruits.

e) It was stated that some of the reaction mixture would be lost through evaporation during heating. Make an addition to your diagram to show how this could be reduced.

This is the wet paper towel wedge shown in the above diagram.

PPA3 - Factors affecting enzyme activity

Aim: The aim is to investigate the effect of pH or temperature changes on enzyme activity.

a) Suggest a method for measuring enzyme activity of an enzyme under conditions of varied pH or temperature.


pH:
Addition of hydrogen peroxide to a test tube containing 3 potato discs. Record the number of bubbles of oxygen given off during a period of 3 minutes with a soluton of pH 7, another of pH 1, and another of pH 13.
Temperature:
Same as pH except the only solution used should be deionised water and 4 experiments should be carried out: one with the water at 30°C, another at 40°C, another at 50°C, and another at 60°C.

b) What measurements would you take?


For both pH and temperature:
- Count and record the number of bubbles of oxygen produced during the first 3 minutes of the reaction
For temperature only:
Measure and record the steady temperature just before adding the hydrogen peroxide.

c) What form would the resulting graph of pH/temperature against enzyme activity take?

The form of a line graph.

Unit 3

PPA1 - Hess's Law

Aim : The aim of the experiment is to confirm Hess's law.

a) What measurements must be taken at each stage?


1. The change in temperature
2. The mass of KOH
3. The mass of acid/water

b) Explain why a plastic beaker is preferable to a metal one.

Plastic performs better as a heat insulator than metal.

c) List any safety precautions you would take.

1. Safety goggles should be worn as the hydrochloric acid will irrate the eyes if contact is made
2. Care should also be taken with the potassium hydroxide as it is corrosive.

d) Before adding together the solutions of acid and alkali, how is the initial temperature determined?

The acid and alkali are each poured into a plastic beaker or polystyrene cup then their temperature is determined with the use of a thermometer.

PPA2 - Quantative Electrolysis

Aim: The aim is to confirm the reaction 2H+(aq) + 2e ----> H2(g), that is to determine the quantity of electricity required to produce one mole of hydrogen by electrolysing dilute sulphuric acid.

a) Draw a diagram of the apparatus used.

Basically, sketch the apparatus in this photo:


b) In order to find the quantity of electricity in order to produce one mole of hydrogen by electrolysis, what measurements have to be made?

96,500C is the charge associated with one mole of electrons.
The mass or volume of an element discharged can be calculated by the quantity of
electricity passed and vice-versa.

c) List any safety precautions you would take.

1. Safety glasses should be worn
2. An alternating current should be used to prevent electric shocks.

PPA3 - A Redox Titration

Aim: The aim is to determine the mass of vitamin C in a tablet by carrying out a redox titration using a solution of iodine of accurately known concentration and starch solution as an indicator.

a) What is meant by a standard solution and how can one be prepared?

A standard solution is a solution of known molarity. One can be prepard by adding some deionised water of a known volume to a vitamin C tablet in a beaker. Add a few drops of starch solution and then add iodine solution from a burette.

b) How could the end point of the titration be determined?

By the colour change from clear to blue/black.

c) List an apparatus needed for such a titration.

-small beaker
- wash bottle
- 250cm cubed standard flask
- filter funnel
- 25cm cubed pipette
- 50cm cubed burette
- conical flask
- pipette filter
- white tile
- standard solution of iodine
- starch solution
- vitamin C tablet
- deionised water

d) From the results of several titrations, including a rough one, what volume of solution would be used in the calculation?

75cm cubed.

[Ally]

Nice work bred.

[bred]

Thanks.
I'm not a Chemistry genius but I think those answers are mostly sufficient.

[someone11]

whats the sulphuric acid for??

[AM4R]

whats the sulphuric acid for??

acts as an catalyst and stops the reversable reaction........i think

[c r smit]

whats the sulphuric acid for??

acts as an catalyst and stops the reversable reaction........i think

sounds about right!

[Rapidfire]

"c) What form would the resulting graph of pH/temperature against enzyme activity take?

The form of a line graph."

Actually it is not a line graph but a parabolic curve which has a maximum turning point at the optimum.

[appujal]

bred, on 05 May 2005 - 09:11 PM, said:

<u><b>PPA Answers</b></u>

<u><b>Unit 1</b></u>

<b>PPA1 - the effect of concentration changes on reaction rate</b>

Aim: The aim is to find the effect of varying the concentration of iodide ions on the rate of reaction between hydrogen peroxide and acidified potassium iodide solution.

a) Suggest a method for measuring the rate of this reaction

<b>Since the amount of thiosulphate ions initially present will be the same in each experiment, the appearance of the blue/black colour will always represent the same extent of reaction. So if t is the time it takes for the blue/black colour to appear then we can take 1/t as a measure of the reaction rate.</b>

b) The experiment was carried out to investigate the effect of iodide ion concentration on reaction rate. Suggest two factors which should be kept constant throughout the experiment.

<b>
1. The concentration of hydrogen peroxide
2. The temperature at which the experiments are performed.</b>

c) How is the course of reaction followed?

<b>The course of this reaction can be followed by carrying it out in the presence of small quantities of starch and sodium thiosulphate solutions.</b>

d) Suggest any safety precautions which should be carried out.

<b>
1. Safety glasses should be worn as both 1 mol l-1 sulphuric acid and 0. 1 mol l-1 hydrogen peroxide irritate the eyes.
2. Syringes should be pointed downwards to prevent inury.</b>

<b>PPA2 - the effect of temperature changes on reaction rate</b>

Aim: The aim is to find the effect of varying temperature on the rate of reaction between oxalic acid and an acidified solution of potassium permanganate.

a) Suggest an experiment to investigate the effect of temperature on the reaction rate - can you name the acid used?

<b>Oxalic acid.</b>

b) Suggest two factors which should be kept constant throughout the experiment.

<b>The concentrations and volumes of the reactants.</b>

c) How is the course of the reaction followed?

<b>Initially the reaction mixture is purple in colour due to the presence of the permanganate ions but it will turn colourless as soon as they are used up.</b>

d) What are the units of reaction rate?

<b>s-1</b>

e) Suggest any safety precautions which should be carried out.

<b>
1. Safety glasses should be worn as both 1 mol l-1 sulphuric acid and 0.1 mol l-1 hydrogen peroxide irritate the eyes.
2. Syringes should be pointed downwards to prevent inury.</b>

<b>PPA3 - The Enthalpy of Combustion</b>

Aim: The aim is to determine the enthalpy of combustion of ethanol.

a) Draw a diagram of the apparatus you would use

<img src='http://img.photobucket.com/albums/v664/bred2k5/ethanol.jpg' border='0' alt='user posted image' />

b) List all the safety precautions you should take

<b>
1. Safety glasses hould be worn.
2. Experiment apparatus should be kept well away from other flammable substances.</b>

c) The experimental value is often much less than the data book value. Give two reasons for this, including one which is not related to heat loss to the surroundings.

<b>
1. Heat was lost to the surroundings.
2. Incomplete combustion of ethanol.</b>

<b><u>Unit 2</u></b>

<b>PPA 1 - Oxidation</b>

Aim: The aim is to use the mild oxidising agents (acidified potassium dichromate solution, Benedict's solution and Tollen's reagent) to distinguish between two given carbonyl compounds, one of which is an aldehyde, the other a ketone.

a) Name suitable oxidising agents and be able to give the colour change involved when they react.

<b>
With aldehydes:
Tollen's reagent gives a silver mirror effect on the side of the test tube.
With Fehling's solution the blue colour transforms into a dark red precipitate of copper (I) oxide.
With ketones:
There is no change.</b>

b) Why is the potassium dichromate acidified?

<b>To increase the number of H+ ions</b>

c) List all the safety precautions you should take

<b>
1. Safety glasses should be worn
2. Gloves should be worn to handle Tollen's reagent and the carbonyl compounds.</b>

<b>PPA2 - making esters</b>

Aim: The aim is to prepare an ester and identify some of the characteristic properties of esters.

a) Describe the function of the sulphuric acid.

<b>Sulphuric acid performs as a strong oxidising agent.</b>

b) Draw a diagram to show how you would heat the mixture

<img src='http://img.photobucket.com/albums/v664/bred2k5/esters.jpg' border='0' alt='user posted image' />

c) Mention any necessary safety precautions

<b>Safety goggles should be worn.</b>

d) Describe how you would detect the presence of an ester

<b>
1. There should be an oily layer on the top of the reaction mixture if an ester is present.
2. The ester should also give off a pleasant smell, similar to that of fruits.</b>

e) It was stated that some of the reaction mixture would be lost through evaporation during heating. Make an addition to your diagram to show how this could be reduced.

<b>This is the wet paper towel wedge shown in the above diagram.</b>

<b>PPA3 - Factors affecting enzyme activity</b>

Aim: The aim is to investigate the effect of pH or temperature changes on enzyme activity.

a) Suggest a method for measuring enzyme activity of an enzyme under conditions of varied pH or temperature.

<b>
pH:
Addition of hydrogen peroxide to a test tube containing 3 potato discs. Record the number of bubbles of oxygen given off during a period of 3 minutes with a soluton of pH 7, another of pH 1, and another of pH 13.
Temperature:
Same as pH except the only solution used should be deionised water and 4 experiments should be carried out: one with the water at 30°C, another at 40°C, another at 50°C, and another at 60°C.</b>

b) What measurements would you take?

<b>
For both pH and temperature:
- Count and record the number of bubbles of oxygen produced during the first 3 minutes of the reaction
For temperature only:
Measure and record the steady temperature just before adding the hydrogen peroxide.</b>

c) What form would the resulting graph of pH/temperature against enzyme activity take?

<b>The form of a line graph.</b>

<b><u>Unit 3</u></b>

<b>PPA1 - Hess's Law</b>

Aim : The aim of the experiment is to confirm Hess's law.

a) What measurements must be taken at each stage?

<b>
1. The change in temperature
2. The mass of KOH
3. The mass of acid/water</b>

b) Explain why a plastic beaker is preferable to a metal one.

<b>Plastic performs better as a heat insulator than metal.</b>

c) List any safety precautions you would take.

<b>1. Safety goggles should be worn as the hydrochloric acid will irrate the eyes if contact is made
2. Care should also be taken with the potassium hydroxide as it is corrosive.</b>

d) Before adding together the solutions of acid and alkali, how is the initial temperature determined?

<b>The acid and alkali are each poured into a plastic beaker or polystyrene cup then their temperature is determined with the use of a thermometer.</b>

<b>PPA2 - Quantative Electrolysis</b>

Aim: The aim is to confirm the reaction 2H+(aq) + 2e ----> H2(g), that is to determine the quantity of electricity required to produce one mole of hydrogen by electrolysing dilute sulphuric acid.

a) Draw a diagram of the apparatus used.

<b>Basically, sketch the apparatus in this photo:</b>
<img src='http://www.labsupply.com.hk/images/Sci-ed%20chem%20electrolysis.jpg' border='0' alt='user posted image' />

b) In order to find the quantity of electricity in order to produce one mole of hydrogen by electrolysis, what measurements have to be made?

<b>96,500C is the charge associated with one mole of electrons.
The mass or volume of an element discharged can be calculated by the quantity of
electricity passed and vice-versa.</b>

c) List any safety precautions you would take.

<b>1. Safety glasses should be worn
2. An alternating current should be used to prevent electric shocks.</b>

<b>PPA3 - A Redox Titration</b>

Aim: The aim is to determine the mass of vitamin C in a tablet by carrying out a redox titration using a solution of iodine of accurately known concentration and starch solution as an indicator.

a) What is meant by a standard solution and how can one be prepared?

<b>A standard solution is a solution of known molarity. One can be prepard by adding some deionised water of a known volume to a vitamin C tablet in a beaker. Add a few drops of starch solution and then add iodine solution from a burette.</b>

b) How could the end point of the titration be determined?

<b>By the colour change from clear to blue/black.</b>

c) List an apparatus needed for such a titration.

<b>-small beaker
- wash bottle
- 250cm cubed standard flask
- filter funnel
- 25cm cubed pipette
- 50cm cubed burette
- conical flask
- pipette filter
- white tile
- standard solution of iodine
- starch solution
- vitamin C tablet
- deionised water</b>

d) From the results of several titrations, including a rough one, what volume of solution would be used in the calculation?

<b>75cm cubed.</b>

Thanks