Test solutions of SCN – of unknown molar concentration. Determine the molar concentrations of the ions present in an equilibrium system. Determine the value of the equilibrium constant, K eq , for the reaction.
LabQuest 10 10 - 2 Chemistry with Vernier MATERIALS Check out from Stockroom Vernier LabQuest LabQuest App In the classroom 0.200 M iron (III) nitrate, Fe(NO 3 ) 3 , solution in 1.0 M HNO 3 Vernier Colorimeter or Spectrometer plastic cuvette 0.0020 M iron (III) nitrate, Fe(NO 3 ) 3 , solution in 1.0 M HNO 3 pipet pump or bulb 50 mL volumetric flask potassium thiocyanate, KSCN solution of unknown concentration 0.0020 M thiocyanate, SCN – plastic Beral pipets tissue six 20 × 150 mm test tubes & test tube rack eight 100 mL beakers PROCEDURE Part I Prepare and Test Standard Solutions 1. Obtain and wear goggles. 2. Obtain small volumes, approximately 35 mL of 0.200 M Fe(NO 3 ) 3 , and 25 mL of 0.0020 M SCN – , in 2 separate small Erlenmeyer flasks. CAUTION: Fe(NO 3 ) 3 solutions in this experiment are prepared in 1.0 M HNO 3 and should be handled with care. Place fresh DI (distilled) water in a wash bottle. Label five beakers: 1 – 5. Prepare the respective five solutions listed in the chart below (The fifth beaker is a blank.). This is done by using a clean 10.0 mL pipet with bulb to transfer the respective Fe(NO 3 ) 3 solution to a 50-mL volumetric flask and a different clean 10.0 mL pipet to transfer the corresponding SCN- solution to the same 50-mL volumetric flask. Now add enough DI water to make exactly 50 mL of solution. Read the bottom of the meniscus to the fill line. Mix each solution thoroughly. Repeat this process for each trial, remembering to clean the volumetric flask thoroughly. Measure and record the temperature of one of the above solutions to use as the temperature for the equilibrium constant, K eq . Beaker number 0.200 M Fe(NO 3 ) 3 (mL) 0.0020 M SCN – (mL) 1 5.0 2.0 2 5.0 3.0 3 5.0 4.0 4 5.0 5.0 blank 5.0 0.0 Note : The fifth beaker is prepared to be used as a blank for your Colorimeter calibration. It will have a slightly yellow color due to the presence of Fe(NO 3 ) 3 . By calibrating with this solution as your blank, instead of distilled water, you will account for this slight yellow color. 3. Prepare a blank by filling a cuvette 3/4 full of the solution in the fifth beaker. To correctly use cuvettes, remember: Wipe the outside of each cuvette with a lint-free tissue. Handle cuvettes only by the top edge of the ribbed sides. Dislodge any bubbles by gently tapping the cuvette on a hard surface. Always position the cuvette so the light passes through the clear sides.