Question

State any three observations which help to determine whether a chemical
reaction has taken place. Write an activity which may justify atleast two of
the listed observations.​

Answer 1

Answer:

Explanation:

Generally, the observations which we observe when a chemical reaction takes place is:

1. Evolution Of Odour
2. Colour change
3. Effervescence takes place

Your question can be explained with the help of an example:

Example : Electrolysis of CuSO4 using platinum electrodes

Electrolyte : CuSO4 in the aq.solution

                    CuSO4 = Cu^2+ + SO4^2-

                     H2O = H^1+ + OH^1-

The ions we get after the dissociation of the compounds is :

Cu^2, SO4^2-, H^1+,OH^1-

Cathode : Cu^2+ + 2e = Cu (Neutral Atom)

Anode : OH^1- - 1e = OH(Neutral Atom)

Final Products: 1. Cathode : Copper

                         2. Anode : Oxygen gas

OH neutral atom is highly unstable in nature so, it combines with another OH neutral atom to liberate oxygen and give water.

2OH + 2OH = 2H2O + O2

Now, with respect to your question the observations that we can see is:

1. At the cathode a pinkish or a reddish brown metal gets deposited.
2. The colour of the electrolyte, that is CuSO4 aq.solution which is initially blue in colour. During the process of electrolysis, the colour of the electrolyte is going to slowly start to fade.