How many atoms are in a sample of 68.7 grams copper (Cu)?

Question

anonymous · Answer

63.5gm Cu contains 6.023 into 10^23 atoms

anonymous · Answer

wouldnt it be 6.51 into 10^23?

anonymous · Answer

No. $$6.023 \times 10^{23}$$ is a constant called Avogadro's number

anonymous · Answer

ya,Avogadros number is 6.022
so you would put 6.022x10^23 + 63.5/1 mol?

jfraser · Answer

no. 1 mole of Cu atoms is 6.022x10^23 atoms, and that pile will weigh 63.5g. You have a pile of copper atoms that weighs more than 63.5g. The conversions have to go:$$68.7g \space Cu * \frac{1mol \space Cu \space atoms}{63.5g \space Cu} * \frac{6.022*10^{23} \space atoms}{1 \space mol \space Cu \space atoms}$$see how all the units except for the # of atoms cancel? The molar mass is the link between the units of mass and quantity.

anonymous · Answer

with the given mass, the number of moles of Cu in the sample can be obtained:

m(Cu)=68.7g
n=m/M
n(Cu)=68.7 / 63.55
        =1.081 moles

1 mole= 6.022x10^23 atoms
so 1.081 moles = (6.022x10^23)(1.081)
                         =6.51x10^23 atoms