# chem

posted by on .

i had posted this question about a week ago and had gotten help from bobpursley(thank you so much btw) but i was showed how to do it using an equationa and now when im studying for the test i realize i need to be able to make a conversion factor to solve it. so heres the problem:

Silver chloride, often used in silver plating, contains 75.27% Ag. Calculate the mass of silver chloride in grams required to make 4.7 g of silver plating.

the equation bob showed me before was
7527*x=4.7g
solve for x

Im just looking how to solve it using a conversion factor. I tried to make one but i didn't know what to do. thanks

• chem - ,

mols Ag needed = grams/molar mass = 4.7/107.9 = 0.04356
moles AgCl = moles Ag x (1 mole AgCl/1 mole Ag) = 1 mole AgCl
g AgCl = moles x (143.34/1 mole) = 0.04356*(143.32) =6.24 grams AgCl.

Note 0.7527*x = 4.7
s = 6.24 grams.

You can string those above into one line and cancel a lot of terms and end up with a conversion factor that is very convenient (its called a chemical factor BUT most profs don't teach it anymore--I used it a great deal when I was a student). It's done this way. We will let MM stand for molar mass.
(g Ag/MM Ag) x (1 mol AgCl/1 mol Ag) x (MM AgCl/1 mol AgCl) =
g Ag x (MM AgCl/MM Ag) = 4.7*(143.32/107.9) = 6.24 g.
You can convert grams of one thing to grams of anything else by using the appropriate chemical factor. In this case, the CF is (143.32/107.9) which is just the ratio of the molar mass of what you want to convert to divided by the molar mass of the starting material.

For example, to convert 2.5 g Mg to grams of Mg2P2O7, we write
2.5 x (molar mass Mg2P2O7/2*molar mass Mg) = 2.5 x (222.55/48.61) = ??. Note I multiplied the Mg by 2 in order to convert to the same number of moles of the metal.

Convert 3.0 g As to As2O5 would be
3.0 x (molar mass As2O4/2*molar mass As) = ??

• chem - ,

thanks!!!