Practical session 3

Question 1

What is the title of practical 3?

Answer 1

Estimation of Oxalate Concentration by Redox Titration.

Question 2

What are the aims for practical 3?

Answer 2

Gain titration experience.

Practice and understand redox titrations.

Question 3

How are titrations known?

Answer 3

Acid-base reactions.

Question 4

What can be titrated except acid and bases in titrations?

Answer 4

A wide range of materials.

Question 5

What is needed in a titration?

Answer 5

A fast chemical reaction.
A stoichiometrically reacted chemical reaction.
A chemical reaction with a clear end point.

Question 6

What happens in the practical 3 in terms of the redox reaction?

Answer 6

It reacts slowly at room temperature.

It needs warming at 80 degrees.

Question 7

What happens to the redox reaction if it cools?

Answer 7

It is more slow.

We miss the end point.

Question 8

In what environment can the redox reaction take place?

Answer 8

In acidic medium.

Question 9

What is added to the redox reaction so it can react in an acidic medium environment?

Answer 9

Dilute sulphuric acid.

Question 10

When is the dilute sulphuric acid added to the redox reaction?

Answer 10

Before the solution is warmed.

Question 11

What is the oxalic acid?

Answer 11

Extremely toxic.

Question 12

For what is the oxalic acid responsible at levels below toxicity?

Answer 12

Ailments: Kidney stones, gout.

Question 13

Where can oxalic acid be found?

Answer 13

In potato skins.
Almonds.
Spinach.
Rhubarb leaves.

Question 14

What can be used to find how much oxalic acid is present in the extract from the crumble?

Answer 14

A redox titration with permanganate.

Question 15

Why can we not use an acid-base titration to find how much oxalic acid is present in the extract from the crumble?

Answer 15

Because other acids might be present.

Question 16

What is the potassium permanganate as it decomposes slowly?

Answer 16

Not a primary standard.\

Question 17

What solution is needed to standardise the permanganate?

Answer 17

A standard solution of sodium oxalate.

Question 18

What is the sodium oxalate?

Answer 18

A primary standard.

Question 19

What can we the sodium oxalate for?

Answer 19

To measure an unknown concentration of another known chemical.

Question 20

What are the advantages of primary standards?

Answer 20

They have distinctive characteristics.

They make accurate and reliable assessments of concentration without using specialised equipment.

Question 21

What are the characteristics of primary standards that make them special?

Answer 21

High purity.
Low reactivity with air/surrounding environment.
Low hygroscopicity.
Large molar mass.
Predictable reactivity.

Question 22

What is the reaction between permanganate and sodium oxalate?

Answer 22

2KMnO4 + 5Na2C2O4 + 16H+ –> 2Mn2+ + 10CO2 + 8H2O.

Question 23

What is the stoichiometric relationship between permanganate and oxalate based on this equation?
2KMnO4 + 5Na2C2O4 + 16H+ –> 2Mn2+ + 10CO2 + 8H2O.

Answer 23

2:5.

Question 24

What is the concentration of permanganate in the experiment?

Answer 24

0.02M.

Question 25

What do we have to prepare in the experiment?

Answer 25

A standard solution of sodium oxalate of known concentration.

Question 26

How will we prepare the standard solution of sodium oxalate of known concentration?

Answer 26

Accurately weighing an amount of pure sodium oxalate. Dissolving pure sodium oxalate known amount in a known volume of water. Standardising permanganate solution with dissolved sodium oxalate in water.

Question 27

What will find by using the standardised permanganate solution?

Answer 27

The concentration of an unknown oxalic acid solution.

Question 28

What substance reacts with permanganate and it does not matter if it comes from oxalic acid or sodium oxalate?

Answer 28

The oxalate ion.

Question 29

What will we do in part 1 of the experiment?

Answer 29

Prepare the standard sodium oxalate solution.

Question 30

Which is method of part 1?

Answer 30

Calculate how much sodium oxalate (Na2C2O4, FM = 134 g/mol) is needed to make 100mL of 0.05 M solution. 2. Accurately weigh that amount of sodium oxalate using a 4 place balance, dissolve in ~30 mL of UPW in a beaker. 3. Transfer this solution to a 100mL in a volumetric flask using a small funnel. Remember to rinse the beaker. 4. Make the solution up to the mark with UPW. 5. If the actual weigh of sodium oxalate is significantly different from the weight you calculated (+/- 0.01 g), then calculate the exact molarity of your solution using your exact weight.

Question 31

What will we do in part 2 of the eperiment?

Answer 31

Standardise an unknown Permanganate solution.

Question 32

Which is the method for part 2?

Answer 32

Pipette 25mL of the sodium oxalate solution into a conical flask. Then add ~25mL of 2M sulphuric acid using a measuring cylinder. 2. Warm the flask on a hot plate (about 80 0C). TAKE CARE WITH THESE HOT MATERIALS. 3. While this is heating fill a burette with the approximately 0.02M potassium permanganate solution. 4. Titrate the sodium oxalate with permanganate until a faint purple colour remains. After the first addition, the purple colour may take a little longer to disappear. Note: this colour may disappear with time if you have not reached the end point but reaction has become slow. If this has happened warm the flask again to ensure reaction is complete. 5. Repeat the titration until concordant results (results that agree within 0.1mL) are obtained. 6. Calculate the concentration of permanganate solution. 2 moles of permanganate react with 5 moles sodium oxalate.

Question 33

What will we do in the part 3 of the experiment?

Answer 33

Titrate the solution from rhubarb crumble which contains oxalate.

Question 34

Which is the method of part 3?

Answer 34

the same as the procedure used for the standardisation of the permanganate solution 1. Pipette 25mL of the pre-prepared unknown solution into a conical flask and add 25mL of 2M sulphuric acid using a measuring cylinder. 2. Warm the flask on a hot plate. (about 80 0C). TAKE CARE WITH THESE HOT MATERIALS. 3. Titrate the heated solution with your standardised permanganate solution until a faint purple colour remains (re-read the advice given above) 4. Repeat the titration until concordant results are obtained. 5. Calculate the concentration of oxalic acid in the solution prepared during the practical.