20. What is the hydroxide ion concentration of an aqueous0.00353 M caffeine solu

Question

20. What is the hydroxide ion concentration of an aqueous0.00353 M caffeine solution? The most basic nitrogen atom incaffeine has a Kb of 4.1 x10-4.

21. Amonoprotic acid has a ka = 55x 10-7.What is the [H+] in a 0.060 M solution?

Explanation / Answer

20) R-N + H2O -> RNH+ + OH- so it produces basic solution [OH-] = C, where Kb = C^2/1- = 0.00041 given C = 0.00353 => ^2/1- = 0.1161 => ^2 + 0.1161-0.1161 =0 => = -0.404, 0.288 neglecting negative root = 0.288 => [OH-] = C= 0.00353 *0.288 =0.00101664 so [OH-] =1.016 x 10^-3 ------------------------------------------------------------------------------------- 21) using same procedure as above , we get [H+] = C , Ka = C^2/1- given C = 0.06 Ka =55x10^-7 => ^2/1- = 9.166 x 10^-5 since

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