Asked by Annon

i did a lab on separation of salt and sand. the initial mass that my teacher gave me was the stock mixture that was: salt= 54.79g; sand= 97.90g. after the experiment my mass were as follow: salt= 1.35g; sand= 3.17g.

question #1 was asking about the % composition of the mixture based on the instructors mass. there was even an equation given.

%composition= mass of component/ x100%
mass of sand+mass of salt

my answer was: sand= 65.11 %; salt= 35.88 %

question #2 was the same but with my mass. i got: sand = 70.13%; salt= 29.86%

question 3 was where i am stuck at. it's talking about

"calculate the expected mass of sand and salt in your sample based on the composition data provided by the instructor".
i asked my teacher to clarify and he said," turn the % in question #1 into a decimal and divide it by the mass of sand or salt i got in my lab which was 3.17g and 1.35g. i did that and the # that i got was : sand = 2.03g ; salt = 0.484 g . from there i went to question #4

question #4. "calculate the % error of you measurements of sand and salt based on expected(2.03g, 0.484g) and observed (3.17g, 1.35g) masses."
(equation).
%error=expected mass - measured mass/ x100
expected masss

i plugged in all the #s but got a negative %. i would like to know if i did something wrong throughout my process. i have asked my classmates as well and they all had gotten a different mass so everyones answer will be different. sorry for the big paragraph, i just wanted to make sure that i am doing it right. sorry again.
Answered by DrBob222
If I divide 35.88 by 100 to get 0.3588 and divide that by 1.35 I get 0.266 for salt.
sand = 65.11 (which I would round to 65.12 from the numbers); then 0.6512/3.17 = 0.205
Confirm those values and look at your calculations again.

As for a negative %error, that just means the value is LOWER than expected as opposed to a +%error which is HIGHER than expected.
Answered by Annon
oh so i was doing it right all along but when i calculate the %error for the salt it gives me something like .1.. then you multiply by 100(to get percentage) and it gives you 100+%. are you supposed to get that?
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