0
You visited us 0 times! Enjoying our articles? Unlock Full Access!
Question

Pheromones are compounds secreted by the females of many insect species to attract males. One of these compounds contains $$80.78\%\ C, 13.36\%\ H$$, and $$5.66\%\ O$$. A solution of $$1.0\ g$$ fo this substance in $$8.50\ cc$$ of benzene freezes at $$3.37^{o}C$$. What are the molecular weight and molecular formula of the compound?

$$(\text{f.p. of} \ C_{6}H_{6}=5.5^{o}C,\ K_{f}(C_{6}H_{6})=5.12^{o}C/m)$$

Solution
Verified by Toppr

Elements $$\%$$ by wt $$\%$$ by wt/ At wt $$=X_t$$ $$\dfrac{X_{t}}{X_{min}}$$
$$C$$ $$80.78$$ $$80.78/12=6.73$$ $$6.75/0.3475=19$$
$$H$$ $$13.36$$ $$13.36/1=13.36$$ $$13.36/0.3475=38$$
$$O$$ $$5.56$$ $$5.56/16=0.3475$$ $$0.3475/0.3475=1$$

$$\therefore$$ Empirical formula of the compound $$=C_{19}H_{38}O$$

Empirical wt $$19\times 12+38+16=282$$

Also, $$\triangle T_{f}=K_{f}\times m$$

$$(5.5-3.37)=5.12\times \dfrac{1\ g}{M.W.\times 8.5\times 1.0028}\times 1000$$

$$(d_{benzene}=1.0028\ g/cc)$$

$$\therefore M.w=\dfrac{5.12\times 1000}{8.5\times 1.0028\times 2.13}=282$$

$$\therefore$$ So $$M.F.=(C_{19}H_{38}O)_{1}=\left(\because n=\dfrac{M.w}{E.w}=\dfrac{282}{282}=1\right)$$

$$M.F=C_{19}H_{38}O$$

Was this answer helpful?
0
Similar Questions
Q1
Pheromones are compounds secreted by the females of many insect species to attract males. One of these compounds contains $$80.78\%\ C, 13.36\%\ H$$, and $$5.66\%\ O$$. A solution of $$1.0\ g$$ fo this substance in $$8.50\ cc$$ of benzene freezes at $$3.37^{o}C$$. What are the molecular weight and molecular formula of the compound?

$$(\text{f.p. of} \ C_{6}H_{6}=5.5^{o}C,\ K_{f}(C_{6}H_{6})=5.12^{o}C/m)$$
View Solution
Q2
Phermones are compounds secreted by the females of many insect species to attract males. One of these compounds contains 80.78% C, 13.56% H, and 5.66% O. A solution of 1.0 g of this substance in 8.50 g of benzene freezes at 3.37oC. What are the molecular weight and molecular formula of the compound?
(f.p of C6H6=5.5oC, kf(C6H6)=5.12oC/m)
View Solution
Q3
The freezing point of a solution containing 2.40 g of a compound in 60.0 g of benzene is 0.10oC lower than that of pure benzene. What is the molecular weight of the compound?
[K is 5.12oC/m for benzene]

View Solution
Q4
C6H6 freezes at 5.5oC. At what temperature will a solution of 10.44g ofC4H10 in 200 g of C6H6 freeze?
Kf(C6H6)=5.12oC/m

View Solution
Q5

In a compound C, H and N atoms are present in 9:1:3.5 by weight. Molecular weight of compound is 108. What is the molecular formula of the compound?

View Solution