A student loaded a mixture of compounds onto a silica gel column using 5 mL of dichloromethane as the loading solvent. After running the column using petroleum ether as the eluant and collecting 8 fractions, the student analyzed the contents by TLC to find that all of the compounds in the mixture came off in the first two fractions. In addition, no separation was observed. Choose the statement that BEST describes the error. The sample should be loaded using a maximum 1 mL of CH2Cl2. Petroleum ether was the incorrect eluant. A more polar solvent should have been used. The student should re-run the TLC. It was obviously performed incorrectly. The student packed the column incorrectly.

Petroleum ether was the incorrect eluant.

Explanation:

In column chromatography, there must be a mobile phase (eluant) and a stationary phase(adsorbent column). The mobile phase in this case is petroleum ether while the stationary phase is silica gel.

If no separation is observed, then it simply means that the wrong choice of mobile phase(eluant) was made. If a better choice of eluant is made, it can effectively achieve the separation of the mixture. The components of the mixture have a great affinity towards the petroleum ether hence they moved rapidly through the column and separation was not achieved.

you need to give more information

answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.