Answer to Question #289901 in Organic Chemistry for Didi

Question

When performing a melting point on a solid compound using a melting point apparatus, two melting point determinations were made. One sample, which was 1 mm in height in the capillary, possessed a melting point of 133.0-133.5oC. The other sample was 10 mm in height. What would you expect the approximate melting point to be for this sample, assuming identical heating rates of 1°/min? (Hint: heat is applied from the bottom of the sample) (Give an actual numerical approximation!)(Hint: at what temperature would 1g of ice start melting at? At what temperature would 10g of ice start melting at?)

5. For the same solid compound as the question above, if the 1 mm sample was heated at 10o per minute on a melting point apparatus, what would you expect for an approximate melting point? (note that at this heating rate, the sample will melt rather quickly, but again give an actual numerical approximation)

Answer 1

Atmospheric gases such as nitrogen and oxygen can dissolve in water. The amount of gas dissolved depends on the temperature of the water and the atmospheric pressure at the air/water interface. Hence bubbles along the insides of your water glass.

Impurities, even when present in small amounts, usually lower the melting point and broaden the melting point range. A wide melting point range (more than 5°C) usually indicates that the substance is impure; a narrow melting point range (O. 5-2°C) usually indicates that the substance is fairly pure.