Chemistry Help Forum Calculate the Mass Fractions of Gold and Copper
 User Name Save? Password

 Thread Tools Display Modes
 Oct 2nd 2013, 05:41 PM #1 AK16 Junior Member   Join Date: Oct 2013 Posts: 1 Calculate the Mass Fractions of Gold and Copper A 9.40g wedding band is made up of gold and copper, and has a 4.382x10^22 atoms. Calculate the mass fractions of gold and copper in this 18-carat gold alloy. I have gotten this far: 1) (Au) = gold = x (Cu) = copper = y 9.40g = x + y 2) Ntotal = 4.382x10^22 4.382x10^22 = N(Au) + N(Cu) 3) Divide by Avogadro Number 4.382x10^22/6.022x10^23 = N(Au)/Na + N(Cu)/Na 7.277x10^-2 mol = n(Au) + n(Cu) 4) Find Masses using mol amount 7.277 x 10^-2 mol = m(Au)/M(Au) + m(Cu)/M(Cu) 7.277 x 10^-2 mol = x/(196.97g/mol) + (9.40g-x)/(63.55g/mol) 5) solve for x This is where I am stuck, how do I solve for X?
Oct 2nd 2013, 06:26 PM   #2
bjhopper
Senior Member

Join Date: May 2010
Posts: 491
 Originally Posted by AK16 A 9.40g wedding band is made up of gold and copper, and has a 4.382x10^22 atoms. Calculate the mass fractions of gold and copper in this 18-carat gold alloy. I have gotten this far: 1) (Au) = gold = x (Cu) = copper = y 9.40g = x + y 2) Ntotal = 4.382x10^22 4.382x10^22 = N(Au) + N(C 3) Divide by Avogadro Number 4.382x10^22/6.022x10^23 = N(Au)/Na + N(Cu)/Na 7.277x10^-2 mol = n(Au) + n(Cu) 4) Find Masses using mol amount 7.277 x 10^-2 mol = m(Au)/M(Au) + m(Cu)/M(Cu) 7.277 x 10^-2 mol = x/(196.97g/mol) + (9.40g-x)/(63.55g/mol) 5) solve for x This is where I am stuck, how do I solve for X?

An 18 caret gold alloy contains 75% gold by weight

 Thread Tools Display Modes Linear Mode