C5b-Percentage composition and empirical formula

Question 1

What are empirical formulas?

Answer 1

The simplest ratio of atoms in a compound

Question 2

How would you find the mass of chlorine in 58.5g of NaCl that has 23g of sodium?

Answer 2

Take away the known mass from the total mass (58.5 - 23= 35.5)

Question 3

132g of a compound contains 36g of carbon and 96g of oxygen. How would you find the empirical formula of this compound?

Answer 3

1) Write out symbols
C : O
2)Write out mass
C : O
36g : 96g
3) Divide by molecular mass to find moles
36 ÷ 12 = 3
96 ÷ 16 = 6
4) Simplify ratio if possible
3 : 6
1 : 2
5) Write Empirical formula
CO2

Question 4

A substance is composed of 77.8% Fe and 22.2% O. How would you find the empirical formula?

Answer 4

1) Divide by molecular mass
77.8 ÷ 56 = 1.389…
22.2 ÷ 16 = 1.387..
2) Round if possible
1.4 : 1.4
3) simplify ratio
1 : 1
4) Write empirical formula
FeO

Question 5

How would you find the percentage composition of Na in NaCl?

Answer 5

1) Find the total molecular mass
(23+35.5= 58.5)
2) Divide Na by total mass then x by 100
(23÷58.5) x 100 = 39.32%