"Titration of Unknown Acid"
Acid Base Titration Objective : To calculate the molarity of an unknown acid and the purity of KHP sample using the acid/base titration ___________________________CUT HERE ________________________________ Procedure : PART 1 : (1) Obtain ~80 mL of ~0.1M NaOH into your container. Make sure to report the actual concentration. (2) Obtain ~25mL of unknown acid into a second container. Let me know if you are NOT in a group of three. * Unknown acid is monoprotic. Give two example of monoprotic acid. * What is unknown about this acid? (3) Using a funnel, fill the burette with NaOH. With the waste beaker underneath, turn the knob to fill the tip of the burette with NaOH. Read the initial volume. * Sketch a meniscus and show where you should read. (4) Using the pipette, transfer 10.00mL of unknown into the Erlenmeyer flask. (5) Put 3 drops of phenolphthalein and magnetic stirrer to the Erlenmeyer flask. * Phenolphthalein is an indicator. What does it indicate? How? (6) Under the burette, place the Erlenmeyer on a hot plate and turn on the stir knob. Heat should be OFF. (7) Titrate the unknown acid until the solution turns pink and remains pink. Do not go below the lowest mark on the burette. Refill if you have to. (9) Repeat (4) to (7). Pre-plan the whole lab! You maybe pipetting while the first person is doing the titration. PART 2 : (10) Measure out ~0.5g of impure KHP. Put into Erlenmeyer flask. Impure KHP is made up of KHP and non-acidic impurity. * What is the KHP? Include at least its formula, molar mass, acidity, and drawing of molecular structure. (11) Add ~20mL of water to KHP and mix well. * Is it important that you have exactly 20mL of water? Why/Why not? (12) Using the same set up from part 1, titrate until the solution turns pink and remains pink. * Do you need the indicator? ___________________________CUT HERE ________________________________ Prelab Questions : (PL1) Sketch the set up for titration for part 1. Indicate what compound is where. (PL2) Define half point, equivalent point, and end point and a titration. (PL3) In part 2, if you say the purity of sample is 57%, what does that mean? (Do not use the word “%” in your answer. (PL4) What is the concentration of nitric acid if 35.6mL of 1.00M calcium hydroxide was needed to completely neutralize 20.00mL of nitric acid? (PL5) What is the concentration of sulfuric acid if 35.6mL of 1.00M calcium hydroxide was needed to completely neutralize 20.00mL of sulfuric acid? (PL6) Compare the answers to (PL4) and (PL5). Discuss. Analysis : PART 1 : (A1) Calculate the concentration of unknown acid. Do you want to average the measurements from two titrations or just use one? PART 2 : (A2) Calculate how many grams in your impure KHP sample was indeed KHP. (A3) Calculate the % (by mass) KHP in the sample. Post lab Questions : Part 1: (Q1) What would happen to the final result (state what “final result” is!) it the tip of the burette was not filled when reading the initial volume? (Q2) What would happen to the final answer if you used Ca(OH)2 instead of NaOH and did not know it? (Q4) What would happen to the final result if the Erlenmeyer flask was contaminated with other types of acid? (Q5) Recalculate the concentration of your unknown acid if it was given as diprotic acid. (Q6) Draw a molecular level picture (showing H+’s OH-‘s, H2O’s…) of what’s (and how many’s) in your beaker before, at half point, at equivalent point, and at end point of the titration. Part 2: (Q7) What would have happened to the final result if the impurity in the sample was also acidic? Summary : Part 1: Unknown # _____ Vb_____ Mb_______ Va_______ Ma ______ Part 2 : Sample # ____ % KHP _______