Answer:
The alkyl ether was yet to be totally dried off after the student recrystallize it .
The suggestion to the student is to redry the alkyl ether product and then reweigh
Step-by-step explanation:
Based on the information the likely explanation for the problem that arise is that the alkyl ether was not totally dried after the student recrystallize the product which lead to the increase in mass from 270mg to 280mg gaining extra mass of 10mg (270mg -280mg).
Therefore what would be my suggestion to the student is that they should redry the alkyl ether product again and make sure that the water is totally dried off and then reweigh or weigh the product again for the second time .