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# weighbydiff - Why Weigh by Difference The amounts of solid...

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Why Weigh by Difference? Why Weigh by Difference? The amounts of solid samples weighed in this course are generally small.  I.e., often  500  mg or  less.   Analytical balances can weigh objects with a precision of about  0.2   mg .   For a 500 mg sample, this is  100 x  0.2  /  500  =   0.04 % We generally strive for better than 1% in precision and accuracy in exercises 1% of 500 mg = 5 mg The analytical balance is certainly capable of providing well beyond this level of precision and accuracy What else could keep us from achieving an accuracy of 1%? The  loss of sample loss of sample  in the process of transferring it from one container to the next. The loss of a  10  mg* sample by any means would constitute a  100 x  10  /  500  = 2% error. *  For comparison, a drop of water weighs about 50 mg.
Each time an intermediate container is used, there is a risk of  some of the solid adhering to the container.   This includes a spatula, watch glass, and especially paper.   We would like to avoid the use of an intermediate container. One way to accomplish this is:

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weighbydiff - Why Weigh by Difference The amounts of solid...

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