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.

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.

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?

No problem! Let's go through each question and calculation step by step to see if there were any errors.

Question #1: Calculate the % composition of the mixture based on the instructor's mass.

To calculate the % composition, you need to divide the mass of each component (salt and sand) by the total mass of the mixture, and then multiply by 100%.

Given:
Mass of salt (instructor): 54.79g
Mass of sand (instructor): 97.90g

Total mass = Mass of salt + Mass of sand = 54.79g + 97.90g = 152.69g

% composition of salt = (54.79g / 152.69g) x 100% = 35.88%
% composition of sand = (97.90g / 152.69g) x 100% = 64.12%

Based on your calculation, the % composition of salt should be 35.88%, but you wrote 65.11%. It seems like there might have been a calculation error there.

Question #2: Calculate the % composition of the mixture based on your mass.

To calculate the % composition, you need to do the same calculation as in Question #1, but using the masses you obtained after the experiment.

Given:
Mass of salt (your measurement): 1.35g
Mass of sand (your measurement): 3.17g

Total mass = Mass of salt + Mass of sand = 1.35g + 3.17g = 4.52g

% composition of salt = (1.35g / 4.52g) x 100% = 29.86%
% composition of sand = (3.17g / 4.52g) x 100% = 70.14%

Based on your calculation, the % composition of sand should be 70.13%, which is very close to your answer.

Question #3: Calculate the expected mass of sand and salt in your sample based on the composition data provided by the instructor.

Your teacher instructed you to convert the % composition into a decimal and divide it by the mass of sand or salt you obtained in your lab.

Given:
% composition of sand (instructor): 64.12% (converted to decimal = 0.6412)
% composition of salt (instructor): 35.88% (converted to decimal = 0.3588)
Mass of sand (your measurement): 3.17g
Mass of salt (your measurement): 1.35g

Expected mass of sand = % composition of sand (instructor) x mass of sand (your measurement)
Expected mass of sand = 0.6412 x 3.17g = 2.03g

Expected mass of salt = % composition of salt (instructor) x mass of salt (your measurement)
Expected mass of salt = 0.3588 x 1.35g = 0.484g

Based on your calculation, the expected mass of salt and sand in your sample should be 2.03g and 0.484g, respectively. So, your calculations here are correct.

Question #4: Calculate the % error of your measurements of sand and salt based on expected and observed masses.

To calculate the % error, you need to use the formula:

% error = (expected mass - measured mass) / expected mass x 100%

Given:
Expected mass of sand: 2.03g
Measured mass of sand: 3.17g

% error of sand = (2.03g - 3.17g) / 2.03g x 100% = -55.17%

Expected mass of salt: 0.484g
Measured mass of salt: 1.35g

% error of salt = (0.484g - 1.35g) / 0.484g x 100% = -179.75%

Based on your calculations, you obtained negative percentages for the % error. This can happen when the expected mass is higher than the measured mass. However, it's important to note that negative % errors usually indicate that the measured values are higher than the expected values, which suggests that there might have been some error in the measurement process.

Overall, it seems like there might have been some mistakes in your calculations for the % composition in question #1. Please double-check your calculations, and if you find any errors, correct them and recalculate the subsequent questions.