Question

1. the molecule borazine has an empirical formula of bh₃n. what is the molecular formula if the molecular weight is 80.5 g/mol?
2. in an experiment, a student burned a metal to create a metal oxide.

mass of empty crucible: 21.45
mass of crucible + metal: 23.76
mass of crucible + metal oxide: 26.35

a. what is the mass of the metal?
b. what is the mass of oxygen that is combined with the metal?
c. calculate the empirical formula for the metal oxide if the metal is lithium.

Explanation:

Step1: Calculate the mass of the metal

Mass of metal = Mass of crucible + metal - Mass of empty crucible
$23.76 - 21.45=2.31\space g$

Step2: Calculate the mass of oxygen

Mass of oxygen = Mass of crucible + metal oxide - Mass of crucible + metal
$26.35 - 23.76 = 2.59\space g$

Step3: Calculate the moles of lithium and oxygen

Molar mass of Li = $6.94\space g/mol$, moles of Li=$\frac{2.31}{6.94}\approx0.333\space mol$
Molar mass of O = $16.00\space g/mol$, moles of O=$\frac{2.59}{16.00}\approx0.162\space mol$

Step4: Find the ratio of Li to O

Divide moles of Li and O by the smaller number (0.162)
Ratio of Li: $\frac{0.333}{0.162}\approx2$
Ratio of O: $\frac{0.162}{0.162} = 1$

Answer:

a. The mass of the metal is $2.31\space g$.
b. The mass of oxygen combined with the metal is $2.59\space g$.
c. The empirical formula for the metal oxide (if the metal is lithium) is $Li_2O$.