Question

4. Given the following reaction:

2CrO_4^2-(aq) + 2H+(aq) <----> Cr₂O_7^2- + H₂O(l)

yellow orange

a. What color would a K2CrO4 solution be?

b. If sulfuric acid (H2SO4) is added to this solution, will a color change be observed? If so, how does the addition of sulfuric acid result in a color change? Explain your reasoning by showing the effect of the addition of H2SO4 on the equilibrium for the reaction.

c. If sodium hydroxide (NaOH) is added to the solution, will a color change be observed? If so, how does the addition of sodium hydroxide result in a color change? Explain your reasoning by showing the effect of the addition of NaOH on the equilibrium for the reaction.

Answer 1

a)

we can see that

K2Cr04 solution will be yellow in color

b)

now consider the equilibrium

2 Cr042- + 2H+ ---> Cr2072- + H20

we know that

according to Le Chatlier principle

the equilibrium will shift in a direction to counter the change

now

by adding H2S04 , the concentration of H+ is increased

so

to decrease the H+ concentration the equilibrium will shift to the right

as a result

the color will turn more orange

c)

now

by adding NaOH , H+ ions are removed by the equation

H+ + OH- --> H20

so

to H+ ions are being removed

so

to increase the concentration of H+ , the equilibrium will shift to the left

so

the solution will turn more yellow