chem 2200 vid

Experiment Overview

• Determine the amount of calcium as calcium oxalate monohydrate in an unknown calcium sample.

• Use three samples weighing between 0.35 to 0.38 grams.

Preparation Steps

• Weigh and record masses in 400 mL beakers labeled 1, 2, 3.

• Conduct experiment in the fume hood due to acid use.

Dissolution Process

• Add ~50 mL of 0.1 M hydrochloric acid to each beaker slowly; swirl to mix.

• If necessary, add 10-20 mL more HCl to ensure dissolution of calcium sample.

• Complete volume to ~100 mL with deionized water.

• Add 5 drops of methyl red indicator (red < pH 4.8, yellow > pH 6.0).

Reaction Process

• Add ~20 mL ammonium oxalate while stirring.

• Add ~15 grams of urea, cover with watch glass, boil until indicator turns yellow (approx. 30 min).

Filtration Setup

• Use sintered glass crucibles labeled 1, 2, 3.

• Tare balance before weighing crucibles with Kimwipes to prevent residue.

Filtration Process

• Set up filtration apparatus with 500 mL filter flask; use vacuum.

• Filter solutions into crucibles, washing with cold deionized water to transfer all precipitate.

• Break vacuum carefully before turning it off.

Drying and Weighing

• Place crucibles in a 600 mL beaker, cover, and dispose of rinses.

• Dry in conventional oven at 120°C overnight.

• After drying, measure mass of crucibles with precipitate; use Kimwipes.

Cleaning Crucibles

• Gently scrape precipitate into solid waste container; wash with soap and water.

• Perform acid wash with HCl and nitric acid followed by copious deionized water.

Final Drying and Mass Measurement

• Dry crucibles again at 120°C for 30 minutes.

• Repeat drying/weighing until two mass measurements agree within ±0.0003 grams.

• Transfer cleaned, dried crucibles to labeled beaker, then back to student locker.