17. 0.56/0.56 points l Previous Answers Chang11 12 EOCP057. My Notes Ask Your Te

Question

17. 0.56/0.56 points l Previous Answers Chang11 12 EOCP057. My Notes Ask Your Teacher Pheromones are compounds secreted by the females of many insect species to attract males. One of these compounds contains 80.78 percent C, 13.56 percent H, and 5.66 percent o. A solution of 1.00 g of this pheromone in 8.50 g of benzene freezes at 3.37°C. What is the molecular formula of the compound? Help chem Pad Greek v H38o Correct. What is the molar mass of the compound? (The normal freezing point of pure benzene is 5.50°C.) 282.5 g/mo Supporting Materials i Supplemental Data Periodic Table Constants and Factors

Explanation / Answer

number of moles of C = mass/molar mass

= 80.78 / 12

= 6.73 moles

Number of moles of H = 13.56 / 1 = 13.56 moles

Number of moles of O = 5.66 / 16 = 0.35 moles

So the ratio of number of moles of C , H & O = 6.73 : 13.56 : 0.35

= ( 6.73/0.35) : (13.56/0.35) : (0.35/0.35)

= 19 : 39 : 1

So emperical formula is C19H39O

Emperical mass is = ( 19x12) + ( 39x1) + 16 = 283

--------------------------------------------------------

We know that T f = Kf x m
Where

T f = depression in freezing point

        = freezing point of pure solvent – freezing point of solution

        =5.50 - 3.37

= 2.13 oC

K f = depression in freezing constant = 5.12 oC/m

m = molality of the solution

    = ( mass / Molar mass ) / weight of the solvent in Kg

= ( 1 / M ) / (8.50x10-3)

= 117.6/M

Plug the values we get 2.13 = 5.12x (117.6/M)

M = 282.8 g/mol

~ 283 g/mol

So n = molar mass / emperical mass = 283 / 283 = 1

So molecular formula is C19H39O

Related Questions

Navigate

• Browse (All)
• Browse 1
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.