/n CHEM 161 Part A Postlab Report Remember that your postlab must be typed and submitted online. The calculations can be handwritten, but they should be inserted into this document (as

pictures) when you submit this report. Remember to use the Lab Introduction document to help you throughout the postlab! There are some helpful equations, definitions, and information in the introduction!!! Remember to keep ALL UNITS AND ALL SIG FIGS in mind! 1. Fill in the following table: Trial Initial VHCI Final VHCI Total HCl volume (mL) Molarity of HCI (mol/L, M) Moles of HCI (moles) Moles of NaOH delivered (moles) Initial VNaOH Final V NaoH Total NaOH volume delivered (mL) Molarity of NaOH (mol/L, M) Average concentration of NaOH (mol/L, M) Standard Deviation of NaOH Lab 3 - Titrations concentration Qualitative comments 0.55 25.10 24.55 0.09965 0.10 26.80 26.70 1 10.50 36.10 25.60 28.20 28.00 2 The base much pinker than trial 2 The base is much lighter than trail 1 a. Type out the chemical equation occurring between NaOH and HCl: b. Show your calculation for moles of HCl delivered for Trial 2 1 c. Show your calculation for moles of NaOH delivered for Trial 2 Lab 3 - Titrations CHEM 161 d. Show your calculation for Molarity of NaOH for Trial 2 2 e. Show your calculation for average and standard deviation for NaOH concentration 2. Using your qualitative comments (color), discuss whether your experimentally determined [NaOH] for each of your trials is higher / lower than the true [NaOH]. EXPLAIN your reasoning. (HINT: remember the things that you MEASURED. How were the MEASURED values affected by your observation of color?) The experimentally determined [NaOH] would be than the true [NaOH]. This is because 3. Discuss the effect of each of these "experimental errors" on the calculated concentration of sodium hydroxide (your answer should tell if the experimentally determined [NaOH] would be higher / lower / equal to the true [NaOH]). EXPLAIN your reasoning. See your calculation work to help you think through these! HINT: remember the things that were MEASURED. How were the MEASURED values affected by each of these experimental errors? How do the MEASURED values affect the final calculated [NaOH]? a. A student places 23.56 mL of HCl to the flask, then she spills about 2 or 3 mL of DI water into the flask. The rest of the titration is done correctly. The experimentally determined [NaOH] would be than the true [NaOH]. This is because d. b. A student forgets to rinse the base-buret with base (then dispose of it), and so there was a slight excess of water in the buret when he began titration trial 1. The rest of the titration is done correctly. The experimentally determined [NaOH] would be than the true [NaOH]. This is because C. A student obtains 25.67 mL of HCl, but a few drops of the HCl splash out of the reaction The experimentally determined [NaOH] would be than the true [NaOH]. This is because e. A student overshoots the titration, and the endpoint is a dark pink. They decide not to back titrate and decide to call it "good." The experimentally determined [NaOH] would be than the true [NaOH]. This is because Lab 3 Titrations CHEM 161 Part B 1. Fill in the following table: Acid ID: 2 n= 3 Mass of unknown acid (g) Initial VN₂OH Final VNaoH TOTAL NaOH volume delivered (mL) TOTAL moles NaOH delivered (mol) Initial VHCI (if back titration needed) Final VHCI (if back titration needed) TOTAL HCI volume delivered (mL) (if back titration needed) Moles of HCI added (if back titration needed) Moles of NaOH reacted with added HCI (if back titration needed) Moles of NaOH reacted with unknown acid (if back titration needed) Moles of unknown acid (mol) Calculated molar mass of unknown acid (g/mol) 0.249 12.10 pl 0.10 p2 47.85 pl 2.45 p2 38.10 X X X Trial 1 X X 0.280 0.20 42.52 42.52 X X X X X Trial 2 3 Lab 3 Titrations CHEM 161 Average molar mass of unknown acid (g/mol) Qualitative comments More NaOH than trial 2 Less NaOH than trial 1 a. Type out the chemical equation occurring between NaOH and your unknown acid (either HA, H₂A, or H3A) b. Show your calculation for moles of NaOH delivered for Trial 2 b.5. ONLY IF YOU BACK TITRATED WITH HCl – show your calculations for the number of moles of HCl added, and the number of moles of NaOH that reacted with the excess HCl. c. Show your calculation for moles of unknown acid in Trial 2 d. Show your calculation for molar mass of the unknown acid for Trial 2 4 e. Show your calculation for average molar mass of the unknown acid 2. Using your qualitative comments, discuss whether your experimentally determined molar mass for EACH TRIAL is higher / lower / equal to the true molar mass. EXPLAIN your reasoning. HINT: remember the things that you MEASURED. How were the MEASURED values affected by your observation of color? The experimentally determined molar mass of the unknown acid is of the unknown acid. This is because 3. Discuss the effect of each of these “experimental errors" on the calculated molar mass of the acid. Discuss whether the experimentally determined molar mass would be higher / lower / equal to the true molar mass. EXPLAIN your reasoning. than the true molar mass HINT: remember the things that were MEASURED. How were the MEASURED values affected by each of these experimental errors? How do the MEASURED values affect the final calculated MMacid? The experimentally determined molar mass of the unknown acid would be molar mass of the unknown acid. This is because a. A student dissolves the unknown acid in 60 mL of water, then she spills about 2 or 3 mL of extra water into the flask. The rest of the titration is done correctly. than the true The experimentally determined molar mass of the unknown acid would be molar mass of the unknown acid. This is because b. After dissolving the unknown acid in water, and after doing the titration, the student notices that there is some solid acid stuck to the side of the flask that never made it into the titration solution. than the true Lab 3 Titrations CHEM 161 5 c. A student overshoots the titration, and the endpoint is a dark pink. They decide not to back titrate, and decide to call it "good." The experimentally determined molar mass of the unknown acid would be molar mass of the unknown acid. This is because than the true Lab 3 Titrations