How does Na2S2O3 react with iodine in the lab experiment for lipids?

Question

is Na2S2O3 oxidize?

Answer 1

Are you trying to determine the Iodine Number?
Here is a hint that you might have missed:
An oxidizing agent is reduced.
A reducing agent is oxidized.
Therefore, you have two choices:
Iodimetry and Iodometry.
Refer to any Analytical Chemistry Textbook for an in depth explanation.
.

Answer 2

2Na2S2O3 + I2 -----> Na2S4O6 + 2NaI

This is a very well-known redox reaction, in which iodine oxidises thiosulphate to tetrathionate.

The end-point is usually detected by adding a bit of starch, and the absence if a blue colour then marks the end-point.