Acompound containing 74.0% carbon, 8.7% hydrogen and 17.3% nitrogen. determine the
empirical formula.
if the compound above has a molar mass of 162.1g/mol. determine the molecular formula of the compound

The empirical formula is C5H7N ; the molecular formula is C10H14N2

Explanation:

in 100% compound we have 74.0 % Carbon ( Molar mass = 12g/mole), 8.7% hydrogen ( Molar mass = 1.01 g/mole) and 17.3% Nitrogen (Molar mass = 14.01 g/mole).

Carbon: 74g / 12 = 6.1667

Hydrogen: 8.7/ 1 = 8.7

Nitrogen: 17.3/ 14. = 1.236

⇒1.236 is the smallest so we divide everything through by 1.236

C: 6.1667 / 1.236 =  4.99 ≈ 5

H: 8.7 /1.236 = 7

N: 1.236 / 1.236 = 1

The empirical formula = C5H7N

To find the molecular formula, calculate the molar mass of the empirical formula first.

C= 12g/mole

H=1g/mole

N=14g/ mole

5*12 + 7*1 + 14 = 81

In this case, 81 g/mol. Compare this to the molar mass given in the problem (162 g/mol). The molecular molar mass is twice the empirical molar mass (162/81 = 2), so the subscripts for the molecular formula should be twice that of the empirical formula

The molecular formula = C10H14N2 ( which is Nicotine)

1. for the first question, we must find the mass of the anhydrous salt, mgso₄. the molar mass for mgso₄·7h₂o is 246.47 g/mol, while that of mgso₄ is 120.37 g/mol.7.834 g mgso₄·7h₂o * 1 mol mgso₄·7h₂o/246.47 g * 1 mol mgso₄/1 mol mgso₄·7h₂o * 20.37 g mgso₄/mol = 0.647 g mgso₄

2. mass of water = mass of sample - mass of anhydrous salemass of water = 7.834 - 0.647 = 7.19 gpercent water in hydrate = 7.19/7.834 * 100 = 91.74%