Question

A typical deposit of cholesterol,C27H460,in an artery has a mass of 3.90mg.how many molecules of cholesterol are present in this deposit?

Answer 1

Answer:

6.074 X 10¹⁸ molecules.

Explanation:

Molecular mass(MM) of this compound C₂₇H₄₆O

= 27*(MM of C) + 46*(MM of H) + (MM of O)

= 27*(12.0107) + 46* (1.00784) + (15.999)

= 324.2889 + 46.36064 + 15.999

=386.64854 g

The mass of a mole of any compound is called it's molar mass. 1 molar mass has 6.022 X 10²³, or Avogadro's number, C₂₇H₄₆O molecules.

If 386.64854 g of C₂₇H₄₆O has 6.022 X 10²³ molecules of  cholesterol, then

3.9mg or 0.0039g of C₂₇H₄₆O will have how many molecules?..

Using unitary method:

Number of molecules = $\frac{0.0039 * 6.022 *10^{23} }{386.64854}$

= 6.074 X 10¹⁸ molecules.