Question #0c5e8

First change percent to mass. If there was 100 grams of the sample, there would be 100 grams.

So 87.4 % nitrogen would be 87.4 grams of nitrogen.

To find the moles of nitrogen divide the mass of 87.4 grams by the molar mass of nitrogen 14 grams/ mole This gives

# 87.4/ 14 = 6.24# moles nitrogen.

100 grams - 87.4 grams = 12.6 grams this would be the mass of Hydrogen. To find the moles of Hydrogen divide the mass of 12.6 by the molar mass of hydrogen.

# 12.6/1 = 12.6 # moles of hydrogen

To find the ratio of Nitrogen to Hydrogen in the empirical formula divide the moles of Hydrogen by the moles of Nitrogen

# 12.6/6.24 = 2.0 Hydrogen atoms: 1.0 Nitrogen atoms.

# N_1H_2# This is not the molecular formula because the empirical formula is not balanced # N^(-3) + 2 xx H^(+1) = +1 #

It would be helpful if the mass was given for the gas. Calculating the new volume using the combined gas law looks like this.

# (V_1 xx P_1)/T_1 = V_2 xx P_2/T_2#

#V_1 = 1 liters#
#P_1 = 710# torr
#T_1 = 373 ^oK#
# V_2 = unkown#
#P_2 = 760#torr
#T_2 = 273^oC#

# 1 xx 710/373 = V_2 xx 760/273 # gives

V_2 = .68 liters.

So the new density at STP is .997 grams/.68 liters. which reduces to

1.47 grams / l liter changing this to the molar volume at STP gives

1.47 x 22.4 = 32.8 grams per mole. Dividing the grams per mole by the grams per empirical formula of #NH_2# or 16 grams gives

# 32.8 /16 = 2 emperical formulas or 2 xx N H_2# =# N_2H_4#