All required calculations must have the correct number of signifleant figures and units. tme axes, data points, and lines on the graph may be drawn in pencil, but all else must be using a pen. 1. Graph (use the graph paper at the back of this manual) The graph can be drawn in pencil, but calculations done on the graph paper must be in pen. The rest of the Postlab assignment form must also be in pen. This graph must conform to the guidelines given at the front part of this manual, "Graphs", turn it in with the Postlab assignment sheet ( 2 marks for drawing the graph properly). ON THE GRAPH: (a) Calculate the value of the pH at the equivalence point from your graph. (0.5 mark) (b) Show the pH range over which the indicator you chose for the replicate titrations would change colour. (0.5 mark) (c) Show the pH range where values of pH are changing most rapidly. (0.5 mark) (d) Calculate the value of Ka from the measured pH values. (0.5 mark) 2. For each titration, calculate the moles of base needed to neutralize the acid sample. Give your calculation for Run I here: ( 0,5 mark) Calculation for Run li Run number moles of NaOH needed 3. (a) Enter your unknown acid code For each run, calculate the molar mass of your unknown acid. Show your calculation for Run I here: (0.5.mark) Calculation for Run 1: Run number value of molar mass (g/mol) (b) Based on your OWN resuls, give the value of the molar mass that you want to be marked : (3 marks) (Questions continue on the next page) 4. ( 1.5 marks) Give three differences that might be noted between a titration curve for a strong acid (such as hydrochloric acid in Figure 1) and your titration curve for your unknown acid. 5. ( 0.5 mark) Suppose that you first titrated 25.0mL of 0.500MHCl with 0.500MNaOH and then 25.0mL of 0.500M of your weak acid HA with 0.500MNaOH. How would the titration curves compare at 15mL of NaOH beyond the equivalence points? Explain. 6. Assume that the initial volume of the HA(aq) solution equals the volume of water used to dissolve your solid acid HA. point. (2.5 marks) (b) Compare this value with the one you obtained graphically in Question 1(a). (0.5 mark) ASSESSMENT Prelab assignment (7 marks): Postlab assignment (13 marks): Deductions (if any): TOTAL (max of 20 marks): All required calculations must have the correct number of signifleant figures and units. tme axes, data points, and lines on the graph may be drawn in pencil, but all else must be using a pen. 1. Graph (use the graph paper at the back of this manual) The graph can be drawn in pencil, but calculations done on the graph paper must be in pen. The rest of the Postlab assignment form must also be in pen. This graph must conform to the guidelines given at the front part of this manual, "Graphs", turn it in with the Postlab assignment sheet ( 2 marks for drawing the graph properly). ON THE GRAPH: (a) Calculate the value of the pH at the equivalence point from your graph. (0.5 mark) (b) Show the pH range over which the indicator you chose for the replicate titrations would change colour. (0.5 mark) (c) Show the pH range where values of pH are changing most rapidly. (0.5 mark) (d) Calculate the value of Ka from the measured pH values. (0.5 mark) 2. For each titration, calculate the moles of base needed to neutralize the acid sample. Give your calculation for Run I here: ( 0,5 mark) Calculation for Run li Run number moles of NaOH needed 3. (a) Enter your unknown acid code For each run, calculate the molar mass of your unknown acid. Show your calculation for Run I here: (0.5.mark) Calculation for Run 1: Run number value of molar mass (g/mol) (b) Based on your OWN resuls, give the value of the molar mass that you want to be marked : (3 marks) (Questions continue on the next page) 4. ( 1.5 marks) Give three differences that might be noted between a titration curve for a strong acid (such as hydrochloric acid in Figure 1) and your titration curve for your unknown acid. 5. ( 0.5 mark) Suppose that you first titrated 25.0mL of 0.500MHCl with 0.500MNaOH and then 25.0mL of 0.500M of your weak acid HA with 0.500MNaOH. How would the titration curves compare at 15mL of NaOH beyond the equivalence points? Explain. 6. Assume that the initial volume of the HA(aq) solution equals the volume of water used to dissolve your solid acid HA. point. (2.5 marks) (b) Compare this value with the one you obtained graphically in Question 1(a). (0.5 mark) ASSESSMENT Prelab assignment (7 marks): Postlab assignment (13 marks): Deductions (if any): TOTAL (max of 20 marks)
