What is the molar mass of the alloy?alloy is 25% copper, 50% selenium, 18%indium and 7% galium.?

Question

What is the molar mass of the alloy?alloy is 25% copper, 50% selenium, 18%indium and 7% galium.?

Answer 1

Technically, alloys are not compounds, so the term molar mass should not be used.  That said, the mass = the sum of the atomic weight of each element times its percentage mass

Answer 2

You can not get the molar mass from this information.  What you can determine is the empirical formula, so you will get a "reduced" molar mass.

The alloy will have a composition

Cu(w)Se(x)In(y)Ga(z)

where w,x,y,z are the unknown stoichiometric amounts.  Setting z=1 and the empirical formula becomes is:

Cu(a)Se(b)In(c)Ga

We have these known values:

Cu: 0.25     63.54 g/mol

Se: 0.50     78.96 g/mol

In:   0.18     114.8 g/mol

Ga: 0.07    69.72

The molar mass is a*Cu + b*Se + c*In + Ga so let T equal the molar mass:

T= 63.54a + 78.96b + 114.8c + 69.72

For each element, the percent by mass in the alloy is proportional to the amount of that element in the empirical formula:

For copper, %Cu = 63.54a / T * 100, or

     (0.25)(T) = 63.54(a) or

     (0.25)(63.54a + 78.96b + 114.8c + 69.72) = 63.54a

Solve for a:

     a = 0.41514(b) + 0.60358(c) + 0.36656

            

It now becomes a massive excercise in mathematical substitution, by moving on to the next element:

For Se, %Se= 78.96b/ T * 100, or

     (0.50)(T) = 78.96(b) or

     (0.50)(63.54a + 78.96b + 114.8c + 69.72) = 78.96(b)

     Subsitute the value we got for (a) and then solve for (b):

     b = 2.9078c + 1.76596 and substituting b:

     a = 1.8107c + 1.09969

For In, %In= 114.8c/ T * 100, or

     (0.18)(T) = 114.8(c) or

     (0.18)(63.54a + 78.96b + 114.8c + 69.72) = 114.8(c)

     Substitute in a and b (both are now in terms of c) and solve for c to get:

     c = 1.56167  Solving for a and b

     b =  6.30699

     a = 3.92744

     d = 1.00000

Calculating molar mass:

T = 996 g/mole

This is not the actual molar mass, because we do not know what the true values are for w,x,y,z.  We only know the molar mass is some multiple of 996.  Why?

Consider a compounds diacetone and Crown Ether (12-Crown-4:

Diacetone:  C6H12O2

12-Crown-4 : C12H24O4

Both have the exact same percentages by mass of carbon, oxygen, and hydrogen, but they are two different compounds with two different molar masses.  However, they both have the same emperical formula:

C3H8O which has a "reduced" molar mass of 60.094.  Diacetone and 12-Crown-4 therefore have molar masses in multiples of 60.094:

Diacetone: 120.188

12-Crown-4 : 240.376

So, you need to know the structure of the alloy in order to determine the actual molar mass; and this is only useful if the alloy is homogenous.

Answer 3

Here's an online molar mass calculator

http://www.webqc.org/mmcalc.php

Downloadable software - for offline work

http://www.programowaniepc.pl/en/program...