Question 1:  Appendix 7 Chemicals used:  pH used:  pH 4 , 5 ,...

Question 1: 

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The theoretical number of moles of OH- needed to change the pH by one unit (refer to Appendix 7 for a sample calculation and explanation as to why moles are being used) mol A- + mol OH pH; + ApH = pka + log mol HA - mol OH-

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Appendix 7

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Appendix 7: Calculations for addition of a strong base (OH-) into a buffer. When adding a strong base to a buffer, the hydroxide ion will react with the weak acid. HA(aq) + OH-(aq) - A-(aq) + H20(1) (1) This reaction goes close to full completion, therefore the number of moles of A- will increase by the number of OH- moles added. nA- + noH- (2) And the moles of HA decrease by the number of OH- moles added. nHA - nOH- 3) Since the total volume is the same for all the diluted concentrations, the Henderson- Hasselbalch is then: pHi + ApH = pka + log (nA- + nOH- nHA - nOH- (4) The ApH is the change between the buffer pH and the pH after the addition of the strong base. Therefore, pH after the addition of the strong acid (pH,) can be approximated by: PHf = pka + log nA- + noH- (5) HA - nOH- The number of moles of HA and A- can be found by multiplying the total volume added of the chemical by its stock concentration. This means that to find the theoretical moles of OH- the equation changes to: (nHA X 10(PHf-pka)) - nA- nOH- = (6) 1 + 10(PHf-PKa)

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Chemicals used: 

pH used: 

pH 4 , 5 , 6