How much will the pH change in buffer?

NH4Cl added to 0.5L of 0.137M NH3 to give a buffer of 10.34



How much does the pH change if 0.001L of 0.1M HCl were added to 10mL of the buffer?



How much does the pH change if 0.001L of 0.1M HCl were added to 10mL of pure water?How much will the pH change in buffer?
I need to find out how much NH4+ was added to give a pH of 10.34, ( ie a pOH of 3.66, whose OH- = 2.19e-4 molar):



NH3 in water --%26gt; NH4+ %26amp; OH-



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



1.8e-5 = [NH4+] [2.19e-4] / [0.137]



NH4+ = 1.13e-2 molar

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the buffer has:



0.5 litre @ 0.137 mol/litre = 0.0685 moles NH3

0.5 litre @ 1.13e-2 molar = 0.00564 moles NH4+



adding HCl

0.001 litre @ 0.1 mol/litre = adds 0.0001 moles H+,...

which decreases the NH3 %26amp; converts it into NH4+:



0.0685 moles NH3 - 0.0001 moles = 0.0684 moles NH3

0.00564 moles NH4+ + 0.0001 moles = 0.00574 moles NH4+



0.0684 moles NH3 / 0.5 litres = 0.1368 molar NH3

0.00574 moles NH4+ / 0.5 litres = 0.01148 molar NH4+



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



1.8e-5 = [ 0.01148] [OH-] / [0.1368]



[OH-] = 0.000214



pOH = 3.67



pH = 10.33



your first answer : the pH changed - 0.01 ,... from 10.34 to 10.33

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How much does the pH change if 0.001L of 0.1M HCl were added to 10mL of pure water?



0.001L of 0.1M HCl adds 0.0001 moles of H+ ions into 11 millilitres



0.0001 moles H+ ions / 0.011 litres = 9.09e-3 molar H+



pH = 2.04



second answer: the pH drops by 4.96, a change of -4.96, as the pH changes form pure water's 7.00 to this acidified solution ,pH = 2.04

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