# Charge on a penny

## Homework Statement

A 3.0-g copper penny has a positive charge of 67 mC.
What fraction of its electrons has it lost?

## Homework Equations

I don't think im donig this right. i need guidance

## The Attempt at a Solution

i take 3.0 grams * 63.5amu * 6.022 * 10^23 * 29 (electrons) = 3.3*10 ^ 27

67 * 10^-6C / 1.6 * 10 ^ -19C = 4.2 * 10^14

3.3*10 ^ 27/4.2 * 10^14 = WRONG ANSWER. HELP!!!

LowlyPion
Homework Helper

## Homework Statement

A 3.0-g copper penny has a positive charge of 67 mC.
What fraction of its electrons has it lost?

## Homework Equations

I don't think im donig this right. i need guidance

## The Attempt at a Solution

i take 3.0 grams * 63.5amu * 6.022 * 10^23 * 29 (electrons) = 3.3*10 ^ 27

67 * 10^-6C / 1.6 * 10 ^ -19C = 4.2 * 10^14

3.3*10 ^ 27/4.2 * 10^14 = WRONG ANSWER. HELP!!!

A mole of copper atoms will weigh 63.54 grams. 3 grams is what portion of the mole? Then you can go wild with Avogadro and all the orbiting electrons.

ok. would this be correct?

3.0 grams / 63.5amu * 6.022 * 10^23 * 29 (electrons) = 8.2 *10^23

67 * 10^-6C / 1.6 * 10 ^ -19C = 4.2 * 10^14

(4.2 * 10^14)/(8.2 * 10^23) = 5.1*10^-10

Is this correct?

LowlyPion
Homework Helper
ok. would this be correct?

3.0 grams / 63.5amu * 6.022 * 10^23 * 29 (electrons) = 8.2 *10^23

67 * 10^-6C / 1.6 * 10 ^ -19C = 4.2 * 10^14

(4.2 * 10^14)/(8.2 * 10^23) = 5.1*10^-10

Is this correct?

That looks more better as far as your method. I didn't check your math.