CHM1020 Week 9

Name:_________________________________CHM 1020 W9 Lab Show your CALCULATIONS for the numerical problems. Lab 9 Assignment Review of acids/bases and acid-base neutralization : https://www.youtube.com/watch? v=n9wUdgxCLMQ 1. What species is the conjugate acid of HCO 3 – ? Write the formula and net charge. H 2 CO 3 (Net charge=0) 2. Which species is the conjugate base of HPO 4 2– ? Write the formula and net charge. PO 4 3- (Net charge=-3) Refresher of Acid/Base Equilibria, K a , and p K a, and buffer solutions Show your CALCULATIONS for these numerical problems. https://www.youtube.com/watch? v=jdmHjFp_35I 1. The [H 3 O + ] in a cabernet sauvignon wine is 5.9 × 10 –4 M. What is the [–OH] in this wine? [H 3 O+][OH-]=10 -14 5.9 * 10 -4 *[OH-]=10 -14 [OH-]=0.17 * 10 -10 =1.7*10 -11 M 2. The pH of a lime is 1.90. What is the [H 3 O + ]? pH=1.90 -log[H 3 O+]=1.90 [H 3 O+]=antilog (-1.9)=0.012=1.2*10 -2 M 3. What is the pH of a cleaning solution with a [H 3 O + ] = 7.4 × 10 –9 M H 3 O + ? pH=-log 7.4*10 -9 =8.13 4. Normal gastric juice has a pH of about 2. Assuming that normal gastric juice is primarily aqueous HCl, what is the concentration of HCl in the stomach? pH=2 2=-log[H 3 O+] [H 3 O+]= 1.0*10 -2 M = Concentration of HCl 5. The K a of acetic acid is 1.7 × 10 -5 . What is the p K a of acetic acid? K a = 1.7*10 -5 p K a =-log K a p K a =-log(1.7*10 -5 ) = 4.77 6. The p K a of formic acid is 3.750. What is the K a of formic acid? p K a =3.750 p K a =-log K a 3.750=-log K a K a = 1.78*10 -4 Page 1 of 3

Name:_________________________________CHM 1020 W9 Lab Show your CALCULATIONS for the numerical problems. Titrations : Please watch the video on how to set up and perform a titration: https://www.youtube.com/watch?v=sFpFCPTDv2w&t=48s Titration calculation demonstration: https://www.youtube.com/watch?v=2z4mlE6MK0U After the watching these videos, answer the following questions: 1. What is the graduated glass tube used to add the titrant (base) to the analyte (acid)? Burette 2. What is the physical observation when the endpoint has been achieved during titration? Indicator changes color at the endpoint 3. What is the molarity of an HCl solution if 43.6 mL of a 0.125 M NaOH solution are needed to titrate a 25.0 mL sample of the acid according to the equation below (show your calculations) ? NaOH( aq ) + HCl( aq ) → H 2 O( l ) + NaCl( aq ) 43.6 × 0.125 = M HCl × 25 M HCl = 0.218 M Page 2 of 3