2. An unknown white solid has melting point range 119 – 121o C. Benzoic acid is a white solid of 122 o C melting point. How can a student confirm the identity of the unknown solid (is the benzoic acid or not)
Take a mixed melting point with pure benzoic acid. If the unknown is benzoic acid the mixed melting point will not change from the pure stuff. If the unknown is lower it isn't benzoic acid.
I think it is a benzoic acid but it is impure
To confirm the identity of the unknown solid, the student can perform a melting point determination. Here are the steps to follow:
1. Obtain a small amount of the unknown white solid and a small amount of benzoic acid.
2. Set up a melting point apparatus, which typically consists of a melting point capillary and a heating device.
3. Grind both the unknown solid and the benzoic acid into a fine powder.
4. Fill two capillary tubes with the powdered samples. Label one capillary as "unknown" and the other as "benzoic acid."
5. Insert the capillaries into the melting point apparatus, making sure they are securely held in place.
6. Begin heating the apparatus slowly and gradually increase the temperature.
7. Observe the melting behavior of the samples. Look for any signs of melting, such as a change in shape or the appearance of a liquid phase.
8. Record the temperature range at which each sample melts. Take note of any deviations from the expected range.
9. Compare the melting point of the unknown solid with the melting point of benzoic acid.
- If the unknown solid melts within the range of 122 ± 1°C, it is likely benzoic acid, and the student can confirm its identity as such.
- If the unknown solid melts at a significantly different temperature than the known benzoic acid, further analyses may be required to determine its identity.
By comparing the melting behavior and melting point range of the unknown solid with that of benzoic acid, the student can confirm whether or not the unknown solid is indeed benzoic acid.
To confirm the identity of the unknown white solid and determine if it is benzoic acid or not, a student can perform a melting point determination using a technique called melting point analysis. Here's how they can proceed:
Step 1: Prepare the sample
Obtain a small amount of the unknown white solid and crush it into a fine powder. Make sure to keep the sample free from any impurities or contaminants.
Step 2: Set up the melting point apparatus
Assemble the melting point apparatus, which typically consists of a melting point apparatus machine or a melting point capillary tube.
Step 3: Pack the sample into a capillary tube
Using a spatula or a small funnel, carefully transfer a small amount of the powdered unknown solid into a clean and dry melting point capillary tube. Make sure to pack the sample tightly and uniformly inside the capillary tube.
Step 4: Preliminary observations
Before initiating the actual melting point determination, examine the appearance of the unknown white solid. Note its color, texture, and any other physical characteristics that might give some clues about its identity.
Step 5: Perform the melting point analysis
Place the packed melting point capillary tube containing the unknown white solid into the melting point apparatus and start heating it slowly. As the temperature rises, observe the sample closely.
Step 6: Observe the melting point range
Monitor the behavior of the unknown solid during heating. At a specific temperature range, the unknown solid should start to melt and eventually turn into a liquid. Note the temperature range at which this occurs. In this case, the melting range of the unknown solid is given as 119-121°C.
Step 7: Compare with known values
Compare the observed melting point range of the unknown solid (119-121°C) with the melting point of benzoic acid (122°C). If the observed range for the unknown solid falls within the expected range for benzoic acid, it is likely that the unknown substance is benzoic acid. On the other hand, if the observed range differs significantly from the expected range, it is not benzoic acid.
It is important to note that this is a preliminary identification process, and further confirmatory tests such as chemical reactions or spectroscopic analysis may be required for definitive identification of the unknown white solid.