Barbituric acid, hc4h3n2o3 (which we shall abbreviate h-bar), was discovered by the nobel prize-winning organic chemist adolph von bayer and named after his friend, barbara. it is the parent compound of widely used sleeping drugs, the barbiturates. its pka is 4.01. what are the [h+] and ph of a 0.043 m solution of h-bar?

The [H+] is 2.04*10-3 and pH is 2.68

Explanation:

Barbituric acid is a a weak acid. Using Bronsted-Lowry equation, Ka = [H+][A-]/[HA]. we can calculate [H+] , we need to take barbituric acid pKa and apply antilog [-pKa]  (in calculator press button 10x or ^ with negative value pKa). In that way we obtain Ka=9.77*10-5. Considering  [H+]=[A-], we have than:

[H+]=√Ka*Acid Concentration=√9.77*10-5*0.043=2.04*10-3

pH=-㏒[H+]=-㏒[2.04*10-3]=2.7

I hope my answer helps you