How would your percent yield be affected if scraps from an aluminum can were used which is not pure?

The percent ratio of the actual yield to the theoretical yield is known as the percent yield. Generally, the percent yield is lesser than 100 percent as the actual yield is usually less in comparison to the theoretical value.  

In case if the scraps from an aluminum can were used that were not pure then there will be less aluminum comprising product than anticipated. Thus, the percent yield will get reduced.  

69 is the correct math for the amino acids