Respuesta :
Answer : The empirical formula for kevlar is, [tex]C_7H_5NO[/tex]
Solution : Given,
If percentage are given then we are taking total mass is 100 grams.
So, the mass of each element is equal to the percentage given.
Mass of C = 70.58 g
Mass of H = 4.23 g
Mass of N = 11.76 g
Mass of O = 13.43 g
Molar mass of C = 12 g/mole
Molar mass of H = 1 g/mole
Molar mass of N = 14 g/mole
Molar mass of O = 16 g/mole
Step 1 : convert given masses into moles.
Moles of C = [tex]\frac{\text{ given mass of C}}{\text{ molar mass of C}}= \frac{70.58g}{12g/mole}=5.88moles[/tex]
Moles of H = [tex]\frac{\text{ given mass of H}}{\text{ molar mass of H}}= \frac{4.23g}{1g/mole}=4.23moles[/tex]
Moles of N = [tex]\frac{\text{ given mass of N}}{\text{ molar mass of N}}= \frac{11.76g}{14g/mole}=0.84moles[/tex]
Moles of O = [tex]\frac{\text{ given mass of O}}{\text{ molar mass of O}}= \frac{13.43g}{16g/mole}=0.84moles[/tex]
Step 2 : For the mole ratio, divide each value of moles by the smallest number of moles calculated.
For C = [tex]\frac{5.88}{0.84}=7[/tex]
For H = [tex]\frac{4.23}{0.84}=5.03\approx 5[/tex]
For N = [tex]\frac{0.84}{0.84}=1[/tex]
For O = [tex]\frac{0.84}{0.84}=1[/tex]
The ratio of C : H : N : O = 7 : 5 : 1 : 1
The mole ratio of the element is represented by subscripts in empirical formula.
The Empirical formula = [tex]C_7H_5N_1O_1[/tex] = [tex]C_7H_5NO[/tex]
Therefore, the empirical formula for kevlar is, [tex]C_7H_5NO[/tex]
