The melting point of dibenzalacetone is 110-111°C. How many degrees below the lower range shown should you slow down the rate of heating of the melting point apparatus? 1. 10 degrees below 2. 20 degrees below 3. 5 degrees below
The Correct Answer and Explanation is:
To determine when to slow down the heating rate of a melting point apparatus, it’s essential to consider the temperature range at which the substance transitions from solid to liquid. For dibenzalacetone, the melting point is between 110°C and 111°C, which is a narrow range, indicating a relatively sharp melting point.
In general, when determining the melting point of a substance, it is important to heat the sample gradually as it approaches the melting point. If the heating rate is too fast, it can cause the temperature to overshoot the melting point, leading to inaccurate readings. To get an accurate determination, you should slow down the heating rate about 10°C below the expected melting point.
Explanation:
- The melting point range for dibenzalacetone is given as 110–111°C, meaning the temperature at which the substance will change from a solid to a liquid lies within this interval.
- The standard recommendation is to start slowing down the heating rate when the temperature is within 10°C of the expected melting point. This is because as the temperature approaches the melting point, the sample’s phase transition becomes more sensitive to heat, and a rapid increase can lead to inaccurate measurements.
- In this case, 10°C below the lower range (110°C) would be 100°C. This is the point at which you should begin reducing the heating rate to allow for a more precise and accurate reading of the melting point.
Therefore, the correct answer is 1. 10 degrees below. By slowing down the heating rate at this point, you give the sample time to properly transition to its melting phase, resulting in a more accurate measurement of the melting point.
