Use Le' Chatelier's Principle.

Question

this is a solution at equilibrium:
2CrO4^2-(aq)+ 2H^+(aq)< >Cr2O7^2-(aq) +H20

2CrO4^2- yellow
Cr2O7^2- orange

I just have to make predictions of the colour changes when:

a)Add 0.3 M NaOH drop to 5 drops of 0.3 M K2CrO4

b)Add 0.3 M HCl by drop to 5 drops 0.3 M K2CrO4

c)Add 0.3 M N HCl drop to 5 drops of 0.3 M K2CrO7

d)Add 0.3 M NaOH drop to 5 drops of 0.3 M K2CrO7

I think it's:
a)yellow
b)yellow
c)orange
d)orange

I'm really confused please help!What is the difference when you add NaOH and HCl?

Answer 1

Look at the equilibrium reaction. It involves H^+.
So for example, we take K2CrO4 and add H^+ so it drives the reaction to the right, changes CrO4^-2 (which is yellow) to Cr2O4^-2 (which is orange).

Or if we take Cr2O7^-2 (orange) and add NaOH. The NaOH reacts with the H^+, which is on the left side of the equation, that reduces H^+, that shifts the equilibrium to the left and makes CrO4^-2 so the solution turns from orange to yellow.

Answer 2

so lets say for c. HCl adds H+ ions to the product side which makes it more acidic and therefore yellow?

Answer 3

Adding HCl adds H^+ and that drives the reaction to the right. What product and what color are formed on the right?

Answer 4

so i am a bit confused it mainly depends on whether you add H+ (from HCl) or OH- (from NaOH)?

it does not matter whether u add it to CrO4^-2 or Cr2O7^-2?

Because when you add HCl it reacts with H+ which is on the left so the equilibrium moves towards the left and hence yellow

similarly when u add NaOH it reacts with H+ to produce H20. Whne you add it to Cr2O7^-2 the solution turns yellow but when u add it to CrO4^-2 the solution turns orange?

Answer 5

I think you're on the right track because the amount of H+ or OH- affects the equilibrium, which relates to the principle

Answer 6

your wronggg