Question

1)

Which of the following is NOT valid reasoning for these results: A student begins with 5.00 g of an unknown mixture and recovers 2.91 g of copper sulfate and 2.58 g of salicylic acid? (Check all that apply.)

	One or more of the fractions was not fully dried
	The mass of the filter paper was not subtracted from the mass of the crystals
	The reaction spontaneously created more mass

2) What is the percent recovery of the sample if a student dissolves 1.00 g of a mixture of salicylic acid and copper sulfate and recovers 0.62 g and 0.32 g, respectively?

3) What is the percent copper sulfate in a mixture, if 3.21 g of copper sulfate was isolated from a 7.00 g mixture?

4) What percentage of the mixture is salicylic acid if 3.48 g of the acid was isolated from 12.1 g of the mixture?

Answer 1

1.

Answer b) Mass of filter paper was not subtracted from the mass of crystals.

In option a) if one or more of the fraction were not fully dried then total mass of crystals < 5 g

But, 2.91 + 2.58 > 5 g. Hence, not possible.

In options c) Mass is conserved in any process. Hence, not possible.

2.

% recovery = Total mass of crystals obtained / Sample mass * 100

Total mass of crystals obtained = 0.62 g + 0.32 g = 0.94 g

Sample mass = 1 g

% recovery = 0.94 / 1 * 100 = 94 %

3.

Assuming 100 % recovery,

% Copper sulfate = Mass of copper sulfate / Mass of mixture * 100

=3.21 / 7 * 100 = 45.86 %

4.

Assuming 100 % recovery,

% Salicylic acid = Mass of salicylic acid / Mass of mixture * 100

=3.48 /12.1 * 100 = 28.76 %