**USING PERCENTAGE COMPOSITION FOR IDENTIFICATION OF AN UNKNOWN**

In next week’s lab, you will use a version of this week’s procedure to identify an unknown copper compound by determining how much copper it contains. You will calculate the weight percentage of copper in several different compounds, experimentally determine the weight percentage of copper in your unknown, and decide what your compound is.

Remember that weight percentage is the weight of what you are interested in divided by the total weight, and then multiplied by 100. Here is a simplified example, calculating the weight percentage of hydrogen in water:

MW of H_{2}O = [(2 mol H/1 mol H_{2}O) X (1.0 g/1 mol H)] + [(1 mol O/1 mol H_{2}O) X (16 g/1 mol O)]

= 18 g/1 mol H_{2}O

% H in H_{2}O = {[(2 mol H/1 mol H_{2}O) X (1.0 g H/1 mol H)]/[18 g H_{2}O/1 mol H_{2}O)]} X 100

= 11%

Now calculate the weight percentage of copper in the copper sulfate pentahydrate we worked with this week. The molecular formula is CuSO_{4}^{.}5 H_{2}O. To simplify the calculations, use 64 g/mol as the atomic weight for copper and 32 g/mol as the atomic weight for sulfur. Show your work below.

A student receives 1.03 g of an unknown copper compound. After performing all laboratory operations carefully and correctly, he recovers 0.67 g of copper. Could the unknown compound be copper sulfate pentahydrate? Calculate the weight percentage of copper in the unknown to find out. Show your work below and decide what your answer is.

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