Question

Q1. On adding dilute hydrochloric acid to copper oxide powder the solution formed is blue green. Predict the new compound formed which imparts a blue green colour to the solution.
Q2. When potassium iodide solution is added to a solution of lead nitrate in a test tube, a precipitate is formed.
1. What is the colour of this precipitate?
2. Name the compound precipitated.
3. Write a balanced chemical reaction for this.
4. What type of reaction is this?
Q3. The smell and taste of food containing fats and oil changes after sometime. Why does this happen ? Name the process .List two ways which help to slow down the above mentioned process.
Q4. Balance the following chemical equation and also name the type of chemical reaction:
1. HNO3+Ca(OH)2?Ca(NO3)2+H2O2. Pb(NO3)2?PbO+NO2+O2

Answer 1

(1) on adding hcl to Cuo we get CuCl2 + H20
Cuo +2HCl ➡ CuCl2 + H2O
here CuCl2 will impart blue green colour to the solution.

(2) a yellow precipitate of lead iodide is formed.
compound precipitated is lead iodide.
2KI + Pb(No3)2➡PbI2+ 2KNo3
it is a double displacement type of reaction.

(3) it happens because oily food gets oxidized and becomes rancid due to which the smell and taste of food changes.
it can be slowed down by
(a) refrigiration
(b) keeping the food in airtight containers.

(4)2HNo3+ Ca(OH)2➡ Ca(NO3)2+2H2o
2Pb(No3)2➡2PbO + 4NO2+ O2