Question

Part II. 3 UNKNOWN Number: Mass of Acid: 161M NaoH Molarity of NaOH used: 4. Attach the graph of your titration curve with pH vs Volume of NaOH, with proper format and labeling. 5. Calculate the molar mass of your unknown acid using the endpoint for the second step of the reaction between the acid and sodium hydroxide. Show calculations. Molar Mass 6. Write a "B" on your graph to precisely label two points where a buffer exists with similar concentrations of an acid and its conjugate base. At each point, write the formula of the species (based on your probable identity) that are present that contribute to the buffer composition. 7. a) Identify the location on the graph where the concentration of "H2X" is equal to the concentration of "HX". Read the pH at this point on the curve and calculate Kai- Value of Volume at this point Value of pH at this point Kal pKa ) Identify the location on the graph where the concentration of "HX" is equal to the concentration of X2-. Read the pH at this point on the curve and calculate Ka2 Value of Volume at this point Walue of pH at this point pKa O Below are the possible identities of your unknown acid. Determine which acid is likely to be yours an- xplain the reasoning behind your choice. ossible Acids: xalic Acid: H2C2O

Answer 1

5) The molar mass of the acid is calculated:

MM = g / M * V NaOH = 0.1 g / 0.101 * 0.0055 L = 180 g / mol

6) This zone is in the average volume of equivalence:

V 1/2 = 5.5 mL / 2 = 2.75 mL

7) You have the data:

V 1/2 = 2.75 mL

pH = pKa = 4.2

Ka = 10 ^ -pKa = 10 ^ -4.2 = 6.3x10 ^ -5

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