Answer:
Molecular formula = C9H6N3
Explanation:
1. We have to change grams to mol:
C:
1 mol C = 12 g
6.2276 g C ×(1mol/ 12g)= 0.519 mol C
H:
1 mol H = 1 g
1.25382 g H ×(1mol / 1g)= 1.254 mol H
N:
1 mol N = 14 g
2.4344 g N ×(1mol/14 g)= 0.174 mol N
2. Then, you have to divide by smallest number of moles, it is 0.174. You have to approximate the values to integer numbers:
C:
0.519 mol C / 0.174 = 2.983 = 3
H:
1.254 mol H/ 0.174= 1.460 = 2
N:
0.174 mol N/0.174= 1
With this numbers, we obtain the empirical formula C3H2N. Now we gonna calcualte the molecular formula with the empirical formula:
3. Find the molecular weith of empirical formula:
C3 = 12 x 3 = 36
H = 2
N = 14
C3H2N = 36 +2 +14 =52 g/mol
4. Then you have to divide the molecular formula molar mass over the empirical formula mass:
molecular formula molar mass / empirical formula molar mass
To find the molecular formula mass we have to use the ideal gas equation:
PV=nRT
Where:
P= 1023 torr
V = 1.312 ×103 mL
n = mol
R = 0.0821 atmL /molK
T = 98.7 °C
Remeber you have to use the right units for the data, so we gonna change torr to atm, and mL to L and °C to K:
P = 1.35 atm
V = 1.312 L
T = 371.85 K
And replace in the equation:
PV=nRT
1.35 atm ×1.312 L = n ×0.3821×0.0821 atmL/molK ×371.85K
1.784 atmL= n ×30.53 atmL/mol
n= 0.058 mol
And to find the molecular formula molar mass we have to divide de mol n over the grams given on the excersice 9.91582 g:
9.91582g / 0.082 mol = 170.96 g/mol
And now we can use the formula, and the result has to be approximate to a integer number:
molecular formula molar mass / empirical formula molar mass = 3.29 = 3
5. Multiply the whole number with the subscripts of the empirical formula:
C3×3H2×3N1×3 = C9H6N3
To see all the problem solve, with the mathematics explained deeply, please watch the document attached.
Molecular formula = C9H6N3
