Find the number of ibuprofen molecules in a tablet containing 200.0 mg of ibuprofen (c13h18o2). express the amount to four significant figures.

First let us calculate for the molar mass of ibuprofen:

Molar mass = 13 * 12 g/mol + 18 * 1 g/mol + 2 * 16 g/mol

Molar mass = 206 g/mol = 206 mg / mmol

Calculating for the number of moles:

moles = 200 mg / (206 mg / mmol)

moles = 0.971 mmol = 9.71 x 10^-4 moles

Using the Avogadros number, we calculate the number of molecules of ibuprofen:

Molecules = 9.71 x 10^-4 moles * (6.022 x 10^23 molecules / moles)

Molecules = 5.85 x 10^20 molecules

c- cold periods in earth's history during which glaciers covered much of the surface.

explanation: