Question

A compound is 40.050 % sulfur and 59.950% oxygen by mass. This compound is a gas at 35.0 C and 715 mmHg, with a density of 2.98 g/L. Is this compound acidic, basic, or amphoteric? What new compound is formed when the original compound is dissolved in water?

Answer 1

1st find the molar mass of gas using
p*V=n*R*T
p*V=(mass/molar mass)*R*T
p*molar mass=(mass/V)*R*T
p*molar mass=density*R*T
(715/760) atm * MM = 2.98 g/L * 0.0821 atm.L/mol.K * (35+273) K
MM = 80.1 g/mol

now find empirical formula of compound:
Let the total mass be 100 g

mass of S = 40.05 g
mass of O = 59.950 g

number of moles of S = 40.05/32=1.25
number of moles of O = 59.95/16= 3.75

O is 3 times S

So empirical formula= SO3

Empirical formula mass =32+3*16 = 80 g
This is same as molar mass

So the gas is SO3

it is acidic since it is oxide of non metal

SO3 + H2O ---> H2SO4
It forms sulphuric acid in water