E790: Prep Notes
Introduction
A conductivity apparatus is used to measure the equivalence point in a titration of barium hydroxide with sulfuric acid.
H2SO4(aq) + Ba(OH)2(aq) → BaSO4(s) + 2H2O(l)
Supplies
Short List
- Goggles and gloves
- 250 mL beaker
- 50mL buret
- ring stand with buret clamp
- 10-diode array conductivity apparatus
- stir plate and stir bar
- distilled water in wash bottle
Chemicals
- 2.0g Ba(OH)2.8H2O
- 50mL 0.25M H2SO4
Prior to Lecture (prep time ~ 5 min.)
1. Prepare the following chemicals:
- 2.0g Ba(OH)2.8H2O in a 250mL beaker (record weight and include)
- DI in wash bottle
- approx. 50mL 0.25M H2SO4
2. Assemble the following equipment:
- 50mL buret
- 10-diode array conductivity apparatus
- slit open a piece of tubing and enclose the conductivity meter’s lead in it
- stir plate and stir bar
- ring stand with buret clamp and clamp for lead
- goggles
- gloves
To Conduct Demonstration:
- With the conductivity meter lead in the stirring barium hydroxide solution, plug in the conductivity meter. It should indicate that the barium hydroxide solution conducts.
- Begin adding sulfuric acid from the buret. Allow several seconds after each addition.
- As the titration progresses, insoluble barium sulfate will precipitate. The solution will no longer conduct electricity and the diodes will all be dark and stay off in a range of approximately 1mL to either side of the endpoint. The endpoint should take approximately 16 – 20 mL of 0.25M H2SO4 for a 2g sample of Ba(OH)2.8H2O. Be very careful to go dropwise near the endpoint, as it is easy to overshoot it and never have the conductivity meter go completely dark.
- Add excess sulfuric acid to show that the light will go back on.
Set Up
- Situate the 250mL beaker containing 2g of barium hydroxide in 75 to 100 mL of distilled water on the stir plate. Add the magnetic stir bar.
- Cover the beaker with a large piece of Parafim with a slit in it to accommodate the tip of the buret. Do not seal the Parafilm to the beaker top yet.
- Fill the buret with 0.25M sulfuric acid so that acid may be delivered through the hole in the Parafilm while the solution is being stirred.
- Place the lead for the conductivity apparatus inside the beaker, right at the edge of the solution and just under the surface of the liquid. Use the clamp to hold it in place. Seal the beaker with the Parafilm to prevent splattering.
Safety and Disposal
Goggles should be worn.
Care must be taken with the conductivity apparatus to prevent electrical shock. Barium salts are hazardous. A separate barium waste jug is in the demo room.