(a) If 0.1 mol of NH4I is dissolved in water at 25 oC and reach a final volume o

Question

(a) If 0.1 mol of NH4I is dissolved in water at 25 oC and reach a final volume of 1.00 L, please calculate the equilibrium concentration of [OH-] and [H3O+]. Please briefly explain why this salt solution is not neutral.

(b) The autoprotolysis of water is an endothermic reaction. Do you expect the pH of pure water to incerase or decrease with increasing temperature? Please briefly explain.

(c) At 50 oC, Kw = 6.63, please calculate pH of a pure water sample at 50 oC. What is the concentration of [OH-] and [H3O+] in pure water at 50 oC, respectively?

Explanation / Answer

(a) NH4I + H2O ------------->NH4 OH + HI

NH4 OH is a weak base therefore it does not totaly dissociate in water.But HI is a strong acid it totaly dissociate in water and produce hydronium ions . therefore the salt solution is not nutral it is acidic.

[OH-]=1 x10-7 mol dm-3

[H+]= 0.1 moldm-3

(b) it will dicreasing a little while temperature increasing.according to Lechatelier principle the dynamin reaction occurs.though the pH vary there are equal amount of hydroxide and hydronium ions in pure water. There for though pH vary pure water is neutral at any temperature.

(c) pH=6.63(equal to Pkw)// I think you have given Pkw

Kw= [H+][OH-]

pure water these two concentrations are equal

[H+]= antilog-(6.63)

       = 2.34 x 10-7 mol dm-3

[OH-] = 2.34 x 10-7 mol dm-3

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