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A copper salt contains #25.5%# #Cu#, #12.9%# #S#, #25.6%# #O#, and #36.0%# #"water"#...what is the empirical formula of the hydrate?

Answer 1

Wyatt Adkins

#CuSO_4*5H_2O#

We ASSUME that there are #100*g# of copper salt, and work out the molar quantities:

#Cu:# #(25.5*g)/(63.55*g*mol^-1)# #=# #0.401*mol# #Cu#.

#S:# #(12.9*g)/(32.06*g*mol^-1)# #=# #0.401*mol# #S#.

#O:# #(25.6*g)/(15.999*g*mol^-1)# #=# #1.60*mol# #O#

#H_2O:# #(36.0*g)/(18.01*g*mol^-1)# #=# #2.00*mol# #H_2O#

To get the empirical formula, we divide thru by the LOWEST molar quantity, i.e. #0.401*mol#, to give:

#CuSO_4*5H_2O#, #"copper sulfate pentahydrate"#

I've treated this water the same way I would normally treat an element, and I'm free to continue doing so as long as we can measure the actual water loss and dry the salt.

What shade of pink does this salt have?

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Answer 2

Cameron Andrews

The hydrate's empirical formula is CuSO4 · 5H2O.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.