CHEM211 Lecture Notes - Erlenmeyer Flask, Bunsen Burner, Sodium Hydroxide
10 May 2018
School
Department
Course
Professor
Copper in Brass
Materials:
- Beaker (500mL)
-Medicine Dropper
-8 x 200 mL conical flasks.
-Graduated cylinder (10mL and 100 mL)
-Scapula
Preparation of 0.1M Na2S2O3
1. Weight 12.5g of Na2S2O3-5H20 and 0.05g of Na2CO3. → Dissolve in 500 mL of demineralized water. →
Use denver balance for weightings.
2. Add a drop of chloroform.
Preparation of Standard
1. Weight four standards of about 0.2g of clean copper wire into a 200 mL conical flask → Analytical balance.
2. Add 10mL of 6M HNO3 to each in the fume hood, and place on hot plate to dissolve.
3. When dissolution is complete add 3-4 glass beads, add 20 mL of demineralized water and place flask on
bunsen burner. → Boil for 3-4 minutes to remove most of nitrogen oxides.
4. Add demineralized water to avoid bumping and replace evaporative losses.
5. Add 5 mL of 4% Urea to solution and boil for about 1 minute
6. Let the solution cool.
7. Parafilm and Continue next lab?
Preparation of Sample
1. Weigh four samples to the nearest 0.1 mg of approximately 0.2g of brass in 200 mL conical flasks.
2. Dissolve in HNO3 in the fume hood, then add 20 mL of water and boil 3-4 minutes on bunsen burner.
3. Add 3-4 beads to prevent bumping. If brass contains tin white precipitate will remain.
4. Add 5 mL of 4% urea solution, boil for about a minute.
5. Let solution cool.
6. Parafilm and continue next lab?
Prepare 8 packets of 3g of KI.
Preparation of Starch Indication - DAY OF TITRATION
1. Weight 1g of soluble starch → Mix with cool water to produce thin paste.
2. Add to 150 mL of boiling water, and boil solution for about 2 minutes.
Titration of Standard
1. Add 30 mL of water and small portions of 2.5 M NaOH until slight permanent precipitate of Cu(OH)2 forms.
→ Swirl to avoid deposition on upper walls. Intent to have least amount of precipitate.
2. Wear gloves → Weigh out 1.4-1.5g of ammonium acid fluoride (NH4HF2), add to flask and swirl gently until
all precipitate is dissolved. Tilt and roll flask to dissolve.
3. Add 3g of KI and titrate immediately to near the end point with Na2S2O3. → Solution will turn straw yellow
→ Add 5 mL of fresh starch solution and titrate to first permanent disappearance of blue.
4. Empty and rinse flask immediately.
Titration of Sample
1. Add 30 mL of water then add small portions of 2.5 M NaOH until permanent precipitate forms. Swirl gently to
avoid deposition.
2. Weigh out 1.4-1.5g of ammonium acid fluoride (NH4HF2), add to flask and swirl gently until precipitate
dissolves. Tilt and roll flask to dissolve.
3. Add 3g of KI, and titrate immediately to near endpoint. With Na2S2O3 → Straw yellow colour means that
starch needs to be added.
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Document Summary
Preparation of 0. 1m na2s2o3: weight 12. 5g of na2s2o3-5h20 and 0. 05g of na2co3. Dissolve in 500 ml of demineralized water. Use denver balance for weightings: add a drop of chloroform. Boil for 3-4 minutes to remove most of nitrogen oxides: add demineralized water to avoid bumping and replace evaporative losses, add 5 ml of 4% urea to solution and boil for about 1 minute. If brass contains tin white precipitate will remain: add 5 ml of 4% urea solution, boil for about a minute. Preparation of starch indication - day of titration: weight 1g of soluble starch mix with cool water to produce thin paste, add to 150 ml of boiling water, and boil solution for about 2 minutes. Titration of standard: add 30 ml of water and small portions of 2. 5 m naoh until slight permanent precipitate of cu(oh)2 forms. Swirl to avoid deposition on upper walls.
