When heat is absorbed by a system from its surroundings, the value of heat, q, is a positive value

Assume you have been provided following chemicals and equipment to produce gold (Au) nanoparticles,

Chemicals: hydrogen tetrachloroaurate trihydrate, (HAuCl43H2O), sodium citrate dehydrate (Na3C6H5O72H2O), water. Equipment: balance, measurer, hot stirring plate; beaker, and stirrer bar.

1. (a) Write a chemical reaction equation based on above experiment. Explain the reason that causes the color of the colloid. (5 marks)
2. (b) Further experiments show; the red color of the colloid changes to blue by adding 5 drops of 1M NaCl to a vial containing 3 mL fresh gold colloids. However, the red color of Au colloidal does not change if 5 drops of 1M sugar are added. Based on the fact that the citrate anions cover the surface of each nanoparticle, explain what keeps the nanoparticles from sticking together (aggregating) in the original solution. (12 marks)

(c) Why does adding the salt solution (NaCl) produce a different result from adding the sugar solution? (8 marks)