The idea behind these calculations is:

Step 1: Determine whether the additive (in this case NaOH) will react with the acid (HONH₃⁺) or base (HONH₂) of the buffer.

Step 2: Determine how many moles of NaOH you are adding.

Step 3: Determine how many moles of HONH₃⁺ or HONH₂ (which ever the NaOH will react with) are present in the buffer initially.

Step 4: Determine how many moles of HONH₃⁺ or HONH₂ (again which ever the NaOH reacted with) are present after the reaction with NaOH.

Step 5: Convert this back to a concentration by dividing by the final volume of the solution.

Step 6: Use this concentration in the Henderson-Hasselbalch equation to determine the pH of the buffer after the NaOH has been added.

You can work through the first part of the problem by clicking on the test tube below or return to the module and try it on your own.

Click here to work through problem step by step

Will the NaOH react with HONH3+ or HONH2? HONH3+ HONH2 Good! Since NaOH is a base, it will react the the acid present in the buffer (HONH3+). Answer the rest of the questions; there is a check button at the end that will check your calculations when you are done. NaOH is a strong base and will react with an acid. HONH2 is a weak base.
How many moles are present in 1.0 mL 6.0 M NaOH?	moles
How many moles of HONH3+ are present in 100 mL of Buffer A (Buffer A has a HONH3+ concentration of 0.10 M)?	moles
How many moles of HONH3+ are present after reaction with NaOH?	moles
What is the HONH3+ concentration in the buffer after the NaOH has been added?	M
What is the pH of the buffer after the NaOH has been added? (pKa of HONH3+ is 5.96)
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