Suppose a lab group reports a percent yield of sand of 105%. is it really possible to collect more sand than was originally present? what is a possible explanation for the “extra” product? do not consider calculation mistakes; think about the procedure used.

The maximum percent of the product should be 100 percent, so it was not possible to produce a higher than 100 percent yield like 105 percent mentioned in the question. If this happens, then it will be against the law of conservation of energy, that is, mass cannot be created.  

The enhanced mass may have got produced due to impurities. One of the reason is if one has rinsed the container and has left some amount of water. The water is not considered as a substrate, but it may enhance the weight of the result. There is also a probability that some reaction has taken place in the air, and generated liquid or solid substance, which would have increased the weight.