RAMS and Moles

Chemistry - RAMS and Moles

A Mole is a unit of measurement used to express the amount of a substance. It is equal to the number of atoms or molecules in 12g of Carbon-12 (6.023×10^23). -1 This unit of measurement is used instead of grams because one mole of any substance contains the same number of molecules, regardless of its density.

The Relative Atomic Mass of an element is the weighted average mass of the isotopes of the element. It is measured on a scale on which a Carbon – 12 atom has a mass of exactly 12 units.

Relative Formula Mass is the term used to describe the RAM of a compound.

Number of Moles = mass (g)/mass of 1 mole (g)

Percentage Mass of an   = RAM × Number of that element/RFM of compound × 100                               element in a compound

Finding the Empirical Formula of a Compound

1.     List all the elements in the compound

2.     Underneath them, write their experimental masses or percentages

3.     Divide each mass or percentage by the RAM for that particular element

4.     Turn the results into a ratio (by dividing them all by the same number)

5.     Simplify the Ratio until you have it in its simplest form

Empirical Formula Calculations involving hydrated salts

When some substances crystallize from a solution, water becomes chemically bonded to the salt. The salt is said to be hydrated.

Finding the n in BaCl2.nH2O

To find n, the number of water molecules, you have to find the ratio of BaCl2 to the number of moles of water. It’s just another empirical formula!

1.     Find out the masses of water and the other substances in the solution

2.     Divide these by the respective RFM/RAM’s

3.     Turn the results into a ratio

4.     Find the Ratio in its simplest form

Moles in a Solution

A 1M Solution contains 1 Mole per litre; a 2M Solution contains 2 Moles per Litre etc. 

Number of Moles = Volume in Litres × Moles Per Litre of Solution