Question

Methy`1` red has a `K_(a) = 10^(-5)`. The acid form `"Hin"` is red and its conjugate base, `Ind^(Θ)` is yellow. Complete the following table:
`{:("pH",3,5,7),(["Ind"^(Theta)]//["HIn"],-,-,-),("Colour",-,-,-):}`

Answer 1

`10^(-2), 1, 10^(2)`, Red, Orange, Yellow.
i. `pH = 3, [H^(o+)] = 10^(-3)M`
`[("Ind"^(Θ))/("HIn")] = (K_(a))/([H^(o+)]) = (10^(-5))/(10^(-3)) = 10^(-2)`
(Colour of acid form predominates, i.e., red)
ii. `pH = 5, [H^(o+)] = 10^(-5)M`
`:. [("Ind"^(Θ))/("HIn")] = (10^(-5))/(10^(-5)) = 1`
(Colour is mixture of red and yellow, i.e. orange)
iii. `pH = 7, [H^(o+)] = 10^(-7)M`
`[("Ind"^(Θ))/("HIn")] = (10^(-5))/(10^(-7)) = 10^(2)`
(Colour of basic form predominates, i.e., yellow colour)