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Since 1983, pennies have been made with zinc and plated with copper. Prior to 1983, pennies were about 95% copper and 5% tin and zinc. However, from 1793-1837, pennies were pure copper. If you had a penny from 1800 that had a mass of 2.78g, how many atoms of copper would you have?

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Answer:

2.6 x 10 ²² atoms

Explanation:

6.022 x 10²³ atoms ( Avogadro´s number)  are equivalent to 1 mol, so what we need to do in this question is find how many moles of copper 2.78 g represent:

Atomic weight copper = 63.54 g/mol

mol Copper = 2.78 g / 63.54 g/mol = 0.044 mol

# atoms copper = 6.022 x 10²³ atom/mol x 0.044 mol = 2.6 x 10²²

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