Question

3.What is the purpose of sodium sulfate in these extractions?

Answer 1

When you do and extraction with base/acid and water, some of the water is trapped in the layer. Obviously ether and water don't mix but trace amounts of water are still trapped in the ether layer. Sodium sulphate is much happier being hydrated than remaining anhydrous. By adding it to the ether layer any water present will coordination with the Na2So4 forming a hydrated salt. The salt can be removed by simply filtering the solution.The ether layer is now dry . Nearly all the traces amounts of water are removed. when you Rota-vap off the ether to collect your products, it dry.