How many molecules in 0.3g grain of salt ?

Question

How many molecules in 0.3g grain of salt ?

Answer 1

Hi Alex,

This is a simple calculation using the molecular mass of NaCl (salt) to determine the number of molecules.

There are 3 steps;

1) Calculate the molecular mass of NaCl

2) Use the molecular mass to convert g NaCl to moles NaCl

3) Use Avogadro's number to convert moles NaCl to atoms NaCl

 

1) Calculate the molecular mass of NaCl

 

NaCl consists of 1 sodium atom (Na) and one Chlorine atom (Cl).  To determine the molecular mass, we add the atomic masses of these 2 atoms together.  Their masses can be found on the periodic table.

Na = 22.99 g/mol

Cl = 35.45 g/mol

NaCl = 22.99g/mol + 35.45 g/mol = 58.44 g/mol

This tells us that 1 mole of NaCl weighs 58.44g

 

2) Use the molecular mass to convert g NaCl to moles NaCl

We know we have 0.3 g NaCl, but we need to convert that into moles.  We can do this by dividing the number of grams we have by the molecular weight we calculated above.

0.3 g NaCl / 55.44g/mol = 0.0054 moles or 5.4 x 10^-3 moles

 

3) Use Avogadro's number to convert moles NaCl to atoms NaCl

Avogadro's number is a constant that tells us that 1 mole of any substance contains 6.02X10²³ molecules.

All we need to do is multiply the number of moles we have by 6.02x10²³ to determine the number of molecules.

5.4x10^-3 x 6.02 x 10²³ = 3.25 x 10²¹ atoms NaCl