Question

A sample of a chemical substance was decomposed in the laboratory and found to have 29.00g C, 12.17g H, and 33.83g N.

a)Find the molecular formula of this compound if the Formula mass is 62.12 g/mole.
b)Determine how many H atoms would be in a 2.70g sample of this compound.

Answer 1

Given:

Given: Observed mass of C = 29.0 g

Observed mass of H = 12.17 g

Observed mass of N = 33.83

Formula mass = 62.12 g/mol

Molecular formula calculation:

To calculate molecular formula we need the empirical formula.

Empirical formula calculation:

We use given mass to get number of moles, since empirical formula is the simplest mole ratio.

mol C = (29.00 g )/ (12.011 g /mol ) = 2.414 mol C

mol H = (12.17 g )/ (1.0079 g/mol ) = 12.07 mol H

mol N = (33.83 g ) / ( 14.007 g/ mol) = 2.42 mol N

To get simplest mole ratio we divide each moles of atom by smallest number of mole

Smallest mole = 2.414 so we divide each by this number

Number of C = 2.414 / 2.414 = 1

Number H = 12.07 / 2.414 = 5

Number of N = 2.42/2.414 = 1

This gives us empirical formula in that C= 1, H = 5 and N = 1

So formula is CH5N

We know molecular formula = n * empirical formula

n = molecular formula mass/ empirical formula mass

we know molecular formula / formula mass = 62.12 g/mol
empirical formula = Molar mass of C + 5 * molar mass of H + Molar mass of N

= 12.011 g /mol + 5 * 1.0079 + 14.007g/mol

= 61.0575 g/mol

n = Formula mass/ empirical formula mass

= 62.12 g per mol / 61.0575 g per mol

= 1.017

= 1

Molecular formula = n * empirical formula

= 1 * CH5N

Molecular formula = CH5N

b)Determine how many H atoms would be in a 2.70g sample of this compound.

We know the molar mass of compound = 62.12 g/mol. We use that to get moles of compund in 2.70 g.

Number of moles in 2.70 g sample = 2.70 g * 62.12 g per mol = 0.04346 mol compound.

We know each mol of compound there is 1 mol of H so for 0.04346 mol Compound number mol Of H

= 0.04346 mol Compound * 1 mol H / 1 mol Compound = 0.04346 mol H

We know the relation 1 mol H = 6.02 E 23 atoms of H

Let's use this to get number of H atom

Number H atom = 0.04346 mol H * 6.02E23 H atm / 1 mol H

= 2.62E22 H atom.