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February 14, 2003
Materials Needed:
- 0.5 g of Benzoic Acid
- 10 mL of Water
- 50 mL Erlenmeyer flask w/ 1 clamp
- Flutted Filter Paper
- Filter Paper
- Aspirator Kit
- Glass Funnel
- Boiling Water Bath
- 25 mL flask
- Two melting tubes
- Thermometer
- Büchner funnel
- 500 mL Suction flask
- Melting Point Apparatus
Procedure:
Two experiments were ran during this week of lab.
Experiment 1: Crystallization of Benzoic Acid.
- Weighed out 0.5 g of impure benzoic acid.
- Measured 10 mL of distilled water.
- Transfered both to a 125 mL Erlenmeyer flask.
- Heated the mixture in a 100°C water bath.
- Added successive small portions (1 mL) of water while mixture dissolved completely.
- While mixture was being dissolved, we set up a fluted filter paper and placed it in a glass funnel (making sure the funnel was kept warm).
- Placed the funnel in another 125 mL Erlenmeyer flask.
- After mixture (in the hot bath) had completely dissolved and cooled, we poured it in the glass funnel and watched the substance filter.
- As soon as the solution was filtered, we set up the aspirator kit, making sure it was vacuuming properly.
- Poured the remaining solution on the bottom of the Erlenmeyer flask in the Büchner funnel and observed crystals form.
- Scrapped crystals up from the filter paper and placed on a glass plate
- Next week, we will weigh and determine its melting range.
Experiment 2: Determining the Melting Range of Benzaldehyde and Benzoic Acid
- Crushed the benzaldehyde from last weeks lab into a very fine substance.
- Obtained some benzoic acid and crushed it into a very fine substance.
- Placed both the crushed benzaldehyde and benzoic acid into melting tubes.
- Packed the tubes down by dropping them down a long plastic tube onto the counter top.
- Placed the tubes in the Melting Point Apparatus see picture and observed while they melted.
- Once the tubes have melted we determined the melting ranges for both substances.
- Disposed of the tubes in the broken glass container.
Observations:
Experiment 1:
- While heating, we noticed some crystals were forming on the side of the Erlenmeyer flask, this was due to excess swirling.
- For the benzoic acid to completely dissolve, it took more than 20 minutes.
- White/Clear crystals formed at the end of the experiment.
Experiment 2:
- Observed that benzaldehyde began to melt at 85°C and was completely melted at 98°C.
- The benzoic acid began to melt at 122°C and was completely melted at 124°C.
- Melting Range for Benzaldehyde 85-98°C
- Melting Range for Benzoic Acid 122-124°C
- Benzaldehydes melting range was higher than average due to it being impure.
- Benzoic acid has a normal melting range of 122-123°C, our extra one degree in difference might have been caused since the benzoic acid might have been contaminated and therefore was not a pure substance.
- We determined 85% of the benzaldehyde solution turned into crystals (0.70 g / 0.82 g X 100)
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