Question about number of molecules and number of atoms

Question

It would be really appreciated if you can help me with this:

For a 2.2 x 10^-2 grams if glucose (C₆H₁₂O₆)

Find:

a) the number of molecules

b) the total number of atoms

Answer 1

Take the mass and divide by the molar mass and multiply by Avogadro's number.  This will yield the number of molecules.  To get the total number of atoms, multiply the number of molecules you just calculated by 24 atoms of glucose/molecule.  Use two significant figures for your final answers but use every digit on the way to get there.

Pay attention to the units and they should cross out.

 

If you have any questions, let me know.

Answer 2

First work out the molar mass of glucose

 

MM = 6 x 12 + 12 x 1 + 6 x 16 =  180 g

 

The number of moles of glucose is  2.2 x 10^-2 / 160 =  0.0001222 moles of glucose.

 

The number of molecules is this number multiplied by the Avogadro number 6.02 x 10²³   

 

This works out to be 7.358 x 10¹⁹  molecules  

 

Since each glucose molecule has 6 + 12 + 6 = 24 atoms,  the number of atoms is 

 

24 x 7.358 x 10¹⁹  = 1.766 x 10²¹    atoms

Answer 3

(a)

 

1.  Look up the atomic weights of C, H, and O in grams per mole (should be in your chemistry book)

2.  Add 6C + 12H + 6O to get the molecular weight

3.  Divide the given mass by the molecular weight to get number of moles

4.  Multiply number of moles by Avogadro's number (6.02 x 10²³) to get number of molecules

 

(b)

 

There are 6+12+6 atoms in one molecule, so multiply this number by the result from part (a) to get the number of atoms.