Question

In: Chemistry

1.8 grams of ammonia, NH3 (M=18 g/mol), is dissolved in 10L of water. Which best approximates...

1.8 grams of ammonia, NH3 (M=18 g/mol), is dissolved in 10L of water. Which best approximates the pH of the solution? Please explain/show work.

The answer is 7-11.9, but I got 12 and was wondering why it's less than that.

Expert Solution

mass of NH3= 1.8 grams

molar mass of NH3= 18 g/mole

number of moles NH3= mass/molar mass = 1.8/18=0.1 mole

Volume = 10.0L

Molarity = number of moles/volume = 0.1/10= 0.01 M

NH3 + H2O -------------------- NH4+ + OH-

0.01 0 0

-x +x +x

0.01-x +x +x

Kb of NH3 = 1.8x10^-5

kb = [NH4+][OH-]/[NH3]

1.8x10^-5 = x*x/(0.01-x)

for solving the quation

x= 0.000415

[OH-] = 0.000415M

-log(OH-)= -log(0.000415)

POH= 3.38

PH+POH=14

PH= 14-POH

PH= 14-3.38

PH= 14 - 3.38

PH= 10.62.

queen_honey_blossom answered 2 years ago

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