# How to Calculate the Number of Molecules in a Given Amount of Substance

## What is the formula to calculate the number of molecules in a given amount of substance?

How do you determine the number of molecules in a specific mass of a compound like in the example of 322 grams of Cu(NO3)2?

## Formula for Calculating Number of Molecules

To calculate the number of molecules in a given amount of substance, you can use the formula:

N = (m / M) x NA

Where:

N = Number of molecules

m = Mass of the substance in grams

M = Molar mass of the substance in grams per mole

NA = Avogadro's number (6.02 x 10^23)

## Calculating the Number of Molecules in 322 grams of Cu(NO3)2

In the given example of 322 grams of Cu(NO3)2:

The molar mass of Cu(NO3)2 is calculated as follows:

Cu = 1*63g = 63g

N = 2*14g = 28g

O = 6*16g = 96g

Total molar mass = 187g/mol

Using the formula N = (m / M) x NA:

N = (322g / 187g/mol) x 6.02 x 10^23

N = 3.92 x 10^23 molecules

Therefore, there are approximately 3.92 x 10^23 molecules in 322 grams of Cu(NO3)2.