How can I calculate the empirical formula of copper sulfide?

Question

Wyatt Adkins · Accepted Answer

You need to know the mass of one reactant and the mass of the product, or the percent composition of the copper sulfide, in order to calculate the empirical formula for copper sulfide (or any compound, for that matter).

Assume for the first scenario that you are conducting a laboratory experiment in which you heat a copper and sulfur mixture to create a sample of copper sulfide.

Next, you weigh the empty crucible and discover that it weighs 2.077 g; the crucible plus copper and copper sulfide together weigh 2.289 g and 2.396 g, respectively.

Since you are aware that the mass of copper is equal to

#m_("copper") = 2.289-2.077 = 0.212# #"g"#

The mass of copper sulfide is equivalent to

#m_("copper sulfide") = 2.396-2.077 = 0.319# #"g"#

This indicates that the sulfur's mass is

#m_("sulfur") = m_("copper sulfide") - m_("copper") = 0.319-0.212 =0.107g#

The copper sulfide's copper and sulfur percentages are

#"%copper" = 0.212/(0.319)*100% = 66.5%#

#"%sulfur" = 0.107/(0.319)*100% = 33.5%#

This indicates that 66.5g of copper and 33.5g of sulfur are obtained for every 100g of copper sulfide. The mole ratio of the two elements in the formula is then obtained by dividing the percentage of each element by its molar mass.

#66.5# #"g" * ("1 mole")/("63.55 g") = 1.05# #"moles"#

#33.5# #"g" * ("1 mole")/("32.0 g") = 1.05# #"moles"#

Since the mole ratio is #1:1#, your empirical formula is

#Cu_(1)S_(1)#, or #CuS#.

Naomi Aronson · Answer

undefined The mass of copper (Cu) and sulfur (S) in the compound must be known in order to calculate the empirical formula of copper sulfide. Next, you can find the ratio of the elements in the compound by: 1. Finding the mass of copper (Cu) and sulfur (S) in the compound; 2. Dividing the mass of each element by its atomic mass to find the number of moles of each element; 3. Dividing the number of moles of each element by the smallest number of moles to obtain a simple whole-number ratio; 4. Writing the empirical formula using the whole-number ratio found in step 3. For instance, if the mass of copper is 63.5 grams and the mass of sulfur is 32.1 grams, the calculation would be as follows: 1. Cu: 63.5 g
   S: 32.1 g
2. Moles of Cu: 63.5 g / 63.5 g/mol = 1 mo