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?

Answer : The molecular formula of a compound is,

Solution :

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 = 80.78 g

Mass of H = 13.56 g

Mass of O = 5.66 g

Molar mass of C = 12 g/mole

Molar mass of H = 1 g/mole

Molar mass of O = 16 g/mole

Step 1 : convert given masses into moles.

Moles of C =

Moles of H =

Moles of O =

Step 2 : For the mole ratio, divide each value of moles by the smallest number of moles calculated.

For C =

For H =

For O =

The ratio of C : H : O = 19 : 38 : 1

The mole ratio of the element is represented by subscripts in empirical formula.

The Empirical formula =

The empirical formula weight = 19(12) + 38(1) + 1(16) = 282 gram/eq

Now we have to calculate the molar mass of pheromone.

Formula used :  

where,

= change in freezing point

= freezing point of solution =

= freezing point of benzene =

i = Van't Hoff factor = 1  (for non-electrolyte)

= freezing point constant for benzene =

m = molality

Now put all the given values in this formula, we get

Now we have to calculate the molecular formula of the compound.

Formula used :

Molecular formula =

Therefore, the molecular of the compound is,

the answer is b because, investigating whether another species of moth also drinks tears might be interesting, but it would not directly explain why this species of moth does.

to explain why this species of moth drinks tears, the scientist could ask: "what nutrients that moths need are in elephant tears? "

the scientist could experiment with moth repellent or oter ways to keep the moths away, but that would not answer his original question.