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Investigative Analytical Science > Practical session 3 > Flashcards

Practical session 3 Flashcards

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1
Q

What is the title of practical 3?

A

Estimation of Oxalate Concentration by Redox Titration.

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2
Q

What are the aims for practical 3?

A

Gain titration experience.

Practice and understand redox titrations.

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3
Q

How are titrations known?

A

Acid-base reactions.

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4
Q

What can be titrated except acid and bases in titrations?

A

A wide range of materials.

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5
Q

What is needed in a titration?

A

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

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6
Q

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

A

It reacts slowly at room temperature.

It needs warming at 80 degrees.

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7
Q

What happens to the redox reaction if it cools?

A

It is more slow.

We miss the end point.

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8
Q

In what environment can the redox reaction take place?

A

In acidic medium.

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9
Q

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

A

Dilute sulphuric acid.

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10
Q

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

A

Before the solution is warmed.

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11
Q

What is the oxalic acid?

A

Extremely toxic.

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12
Q

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

A

Ailments: Kidney stones, gout.

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13
Q

Where can oxalic acid be found?

A

In potato skins.
Almonds.
Spinach.
Rhubarb leaves.

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14
Q

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

A

A redox titration with permanganate.

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15
Q

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

A

Because other acids might be present.

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16
Q

What is the potassium permanganate as it decomposes slowly?

A

Not a primary standard.\

17
Q

What solution is needed to standardise the permanganate?

A

A standard solution of sodium oxalate.

18
Q

What is the sodium oxalate?

A

A primary standard.

19
Q

What can we the sodium oxalate for?

A

To measure an unknown concentration of another known chemical.

20
Q

What are the advantages of primary standards?

A

They have distinctive characteristics.

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

21
Q

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

A 
High purity.
Low reactivity with air/surrounding environment.
Low hygroscopicity.
Large molar mass.
Predictable reactivity.
22
Q

What is the reaction between permanganate and sodium oxalate?

A

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

23
Q

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

A

2:5.

24
Q

What is the concentration of permanganate in the experiment?

A

0.02M.

25
Q

What do we have to prepare in the experiment?

A

A standard solution of sodium oxalate of known concentration.

26
Q

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

A

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.

27
Q

What will find by using the standardised permanganate solution?

A

The concentration of an unknown oxalic acid solution.

28
Q

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

A

The oxalate ion.

29
Q

What will we do in part 1 of the experiment?

A

Prepare the standard sodium oxalate solution.

30
Q

Which is method of part 1?

A

Calculate how much sodium oxalate (Na2C2O4, FM = 134 g/mol) is needed to make 100mL of 0.05 M solution.

  1. Accurately weigh that amount of sodium oxalate using a 4 place balance, dissolve in ~30 mL of UPW in a beaker.
  2. Transfer this solution to a 100mL in a volumetric flask using a small funnel. Remember to rinse the beaker.
  3. Make the solution up to the mark with UPW.
  4. 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.
31
Q

What will we do in part 2 of the eperiment?

A

Standardise an unknown Permanganate solution.

32
Q

Which is the method for part 2?

A

Pipette 25mL of the sodium oxalate solution into a conical flask. Then add ~25mL of 2M sulphuric acid using a measuring cylinder.

  1. Warm the flask on a hot plate (about 80 0C). TAKE CARE WITH THESE HOT MATERIALS.
  2. While this is heating fill a burette with the approximately 0.02M potassium permanganate solution.
  3. 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.
  4. Repeat the titration until concordant results (results that agree within 0.1mL) are obtained.
  5. Calculate the concentration of permanganate solution. 2 moles of permanganate react with 5 moles sodium oxalate.
33
Q

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

A

Titrate the solution from rhubarb crumble which contains oxalate.

34
Q

Which is the method of part 3?

A

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.

Investigative Analytical Science (16 decks)

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