Techniques to identify molecules

Question 1

What is the overall equation for an iodine-sodium thiosulfate titration?

Answer 1

2S203^(2-)(aq) + I2(aq) -> S4O6^(2-)(aq) + 2I^(1-)(aq)

Question 2

What is reduced in an iodine-sodium thiosulfate titration?

Answer 2

Iodine I2 become 2 I^- ions

Question 3

What is the ratio of sodium thiosulfate to iodine in the titration?

Answer 3

2:1

Question 4

What is oxidised in an iodine-sodium thiosulfate titration?

Answer 4

Sodium thiosulfate ions are oxidised to tetrathionate ions.

Question 5

What is the end point?

Answer 5

The point in a titration in which a definite observable change has occurred. Gives an estimate of the equivalence point but is not always accurate.

Question 6

What is the equivalence point?

Answer 6

The point at which enough titrant has been added that the chemical reaction in the titrant mixture should be completed.

Question 7

Why is a starch indicator used in an iodine-sodium thiosulfate titration?

Answer 7

To aid in identifying the end point. Starch is blue in the presence of I2, so when the reaction is completed, the point at which the solution becomes transparents is clearer than without starch.

Question 8

How can moles of sodium thiosulfate be calculated in a titration?

Question 9

Is the iodine in the burette or the conical flask?

Answer 9

in this prac, the iodine was in the flask, and the sodium thiosulfate in the burette

Question 10

What are some possible sources of error?

Answer 10

• Inaccurate detection of the end-point.
• Equipment not being rinsed properly and containing leftover chemicals.

Question 11

What is the iodine number?

Answer 11

The mass of iodine in grams absorbed by 100 grams of the oil or fat.

Question 12

What are the steps to finding the iodine number?

Answer 12

1. find the mols of the oil
2. multiples mols of oil by number of double bonds in the oil to find total mols of double bonds.
3. mols of iodine = mols of double bonds, so therefore find mass of iodine and therefore iodine number