The Mole and Mass

• Created by: India.02
• Created on: 27-04-19 11:53
• The Mole and Mass
• Relative Formula Mass - Mr
• Percentage mass of an element in a compound
• To calculate the total Mr of a compound, you can just add the Mr's from each atom in the molecular formula
• The Mole
• 6.02 x 10*23 - Avogadro's Constant
• One mole of any substance is the amount of that substance that contains an Avogadro number of particles - so 6.02 x 10*23 particles
• One mole of atoms or molecules of any substance will have a mass in grams that is equal to the relative formula mass of the substance
• This means that 12g of carbon or 44g of CO2 all contain the same number of particles - one mole or 6.02 x 10*23 atoms or molecules
• Carbon has an Ar of 12 - one mole of carbon weighs 12g
• Number of Moles
• Conservation of Mass
• During a reaction, no atoms are destroyed or created - this means that there are the same number and types of atoms on each side of a reaction equation
• Adding the relative formula masses of the substances on each side of a balanced symbol equation allows you to see that all mass is conserved - Mr of reactants = Mr of products
• Change in Mass
• Explanation 1 - increase in mass is probably because one of the reactants is a gas that's found in air and all products are solids, liquids or aqueous
• Before the reaction, the gas is in the air and it isn't part of the reaction vessel - the gas then reacts to form part of the product  and it becomes contained in the reaction vessel - total mass increases
• Explanation 2 - decrease in mass is probably because one of the products is a gas and all the reactants are solids, liquids or aqueous
• Before the reaction, all reactants are contained in the reaction vessel - if the vessel isn't enclosed, the gas can escape as it is formed - no longer contained so you can't account for it's mass - total mass decreases
• Gas will expand to fill the container it is in - if the reaction vessel isn't sealed, the gas will expand out of the vessel and escapes