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Fundamentals

The number of particles in a sample of any substance is related to the mass of the substance. The relationship between these two quantities is made through Avogadro's number and the molar mass of the substance.
 

There are four tables for this difficulty level. Each table has the same basic structure with simply different numerical values. Here is one of the versions:
 

Version 1:

Express your understanding of the conversions between particles, moles, and mass by completing the following table.
 


 

How to Think About This Situation

Help for Wizard Difficulty Level

To complete this table, you will have to calculate the molar mass of each substance and then perform four different types of conversions.

 

Molar Mass Calculations

The molar mass values are entered into the second column of the table. You need to know the substances formula to determine the molar mass; this is given in the first column of the table. The molar mass is calculated by determining the number of atoms of each element in the formula and multiplying this number by the atomic mass of that element. So for the substance NH3, the molar mass is ...
N: 1 x 14.0 g/mol
H: 3 x 1.0 g/mol

which totals 17.0 g/mol.


 

Particle .. Moles .. Mass Conversions

The four different types of conversions are ...
 
  • Particles to Moles Conversion (Rows A and B)
  • Moles to Grams Conversion (Rows A, B, C, and E)
  • Moles to Particles Conversion (Rows C, D and E)
  • Grams to Moles Conversion (Row D)

Each one of these conversions is performed differently. They are described separately in the space below.  

 

Particles to Moles Conversion (Rows A and B)

In Rows A and B the number of particles is given and you must calculate the number of moles of the substance. You must use Avogadro's number to perform this calculation. Avogadro's number is 6.02 x 1023.  This number indicates the number of particles that are in 1 mole. In other words, 6.02 x 1023 particles = 1 mole. This information can be used to form a conversion factor capable of converting from the given number of particles to a number of moles. Here's an example calculation for determining the number of moles of NH3 that is equivalent to 7.51 x 1023 particles of NH3:



 

Moles to Grams Conversion (Rows A, B, C, and E)

In Rows A, B, C and E you will have to determine the mass of the substance in grams. You must know the number of moles and the molar mass of the substance in order to calculate the mass of the substance. The molar mass is calculated in the second column (see above). In Rows C and E the number of moles is explicitly stated. In Rows A and B you will have to first calculate the number of moles from the stated number of particles (see section above). Once you know the number of moles, you will have to use the molar mass to convert the number of moles to the grams of the substance. The molar mass indicates the mass of 1 mole. So if a substance like H2O has a molar mass of 18.0 g/mol, then each mole of H2O has a mass of 18.0 g. You can form a conversion factor from this information and use it to calculate the mass in grams. Here's an example calculation for determining the mass (in grams) of 2.37 moles of NH3  (the molar mass of NH3 is 17.0 g/mol.):





 

Moles to Particle Conversion (Rows C, D and E)

In Rows C, D and E you will have to determine the number of particles. This can only be calculated from the knowledge of the number of moles of a substance. The number of moles is explicitly stated in Rows C and E. But in Row D you will have to first calculate the number of moles from the stated value of the mass of the substance (this is explained in the section below). Once the number of moles is known, the number particles can be calculated using Avogadro's number - 6.02 x 1023.  This number indicates the number of particles that are in 1 mole. In other words, 6.02 x 1023 particles = 1 mole. This information can be used to form a conversion factor capable of converting from the number of moles to a number of particles. Here's an example calculation for determining the number of particles of NH3 that is equivalent to 3.17 moles of NH3:



 

Grams to Moles Conversion (Row D)

In Rows D you will have to determine the number of moles from the mass of the substance in grams. You must know the molar mass of the substance in order to calculate the number of moles. The molar mass is calculated in the second column (see above). The molar mass indicates the mass of 1 mole. So if a substance like H2O has a molar mass of 18.0 g/mol, then each mole of H2O has a mass of 18.0 g. You can form a conversion factor from this information and use it to calculate the number of moles of that substance. Here's an example calculation for determining the number of moles that is equivalent to 48.6 grams of NH3  (the molar mass of NH3 is 17.0 g/mol):





 

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