# Finding the number of electrons in a given substance

ENCgirl

## Homework Statement

I was given this problem in class and I am unable to figure it out:

A copper wire 90.0 cm long and 1.00 mm in diameter has a mass of 6.35 grams.

(a) find the number of electrons in the wire ( Copper has an atomic number of 29; that is there are 29 protons in the copper atom. Copper has an atomic mass of 63.5)

(b) There is one free electron per atom in copper. Find the number of free electrons in the wire.

Me= 9.11e-31

## The Attempt at a Solution

.00635 kg = mass of the wire

(.00635kg) ( 9.11e-31 kg)= 5.8e-33 kg

I really do not know what to do...
Thank you for your help...
K.

Apphysicist

## Homework Statement

I was given this problem in class and I am unable to figure it out:

A copper wire 90.0 cm long and 1.00 mm in diameter has a mass of 6.35 grams.

(a) find the number of electrons in the wire ( Copper has an atomic number of 29; that is there are 29 protons in the copper atom. Copper has an atomic mass of 63.5)

(b) There is one free electron per atom in copper. Find the number of free electrons in the wire.

Me= 9.11e-31

## The Attempt at a Solution

.00635 kg = mass of the wire

(.00635kg) ( 9.11e-31 kg)= 5.8e-33 kg

I really do not know what to do...
Thank you for your help...
K.

Atomic mass is 63.5...so your molar mass is 63.5 g/mol. Do you see how that helps you determine how many moles of copper you have (given your mass)? Then, what do you know about the number of moles and Avogadro's Number?

After all that, you'll know how many atoms of copper you have. Then you can just multiply by the number of electrons per atom for (a) and the number of free electrons per atom (b).

ENCgirl
Thank you sooo much! That helped a lot!