Chemistry Equations

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Seton Hall University
Analytical Chemistry I (CHEM-2215)
Fall 2023
Midterm exam.
(Each answer should be explained in a clear and concise fashion. Please type)
1.
Technician was tasked to prepare 10 mL solution of sodium oxalate in water with 500
ppm approximate concentration. He chooses 50 mL flask (flask weight is 45.000g) and
decided to make this solution in one step using analytical balances with certified accuracy
of 0.05%. He weighed 10.000 g of water in the selected flask and added the necessary
amount of Na2C2O4. He needs to report an exact resulting concentration. How many
significant figures he can report? Carefully explain your thoughts. (What was the weight
of sodium oxalate?)
5 significant figures. An answer is no more precise that the least precise number
used to get the answer.
The weight of the flask (45.000 g) is given to three decimal places. The analytical
balance has a certified accuracy of 0.05%, which means the measurements are
accurate to within 0.05% of the reading. This implies an uncertainty in the weight
measurement.
Weight of water added = 10.000 g Weight of flask = 45.000 g
Now, let’s find the least precise number used to get the answer. In this case, it’s the
weight of the flask, which has an uncertainty of 0.05% of 45.000 g.
Uncertainty in weight of flask = (0.05/100) * 45.000 g = 0.0225 g
So, the weight of the flask can be reported as 45.000 ± 0.023 g.
Now, let’s find the weight of sodium oxalate added. The total weight of the solution
is the …
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