# C4 - Quantitative Chemistry

• Quantitative Chemistry
• The Mole
• the name given to the amount of a substance
• Avogadro's constant = 6.02 x 10'23
• Moles =   mass (g) / Mr
• the mole of an atom or compound is the RAM in grams
• Limiting Reactants
• reactants that get used up first and cause the reaction to stop
• the amount of the product depends on the limiting reactant
• the mass of a product can be calculated by using the mass of a limiting reactant and the balanced symbol equation
• 1) write balanced equation
• 2) work out Mr of the reactant and product you want
• 3) work out moles
• 4) use the number of moles to fin the mass
• Relative Formula Mass
• Compounds have a relative formula mass (RAM / Mr)
• It is the sum of all atomic masses of the atoms in the compound
• %mass of an element in a compound= (At x no atoms in element / Mr of compound ) x100
• The Mole and Equations
• moles can be used to calculate the mass in reactions
• mass=    moles x Mr
• the big numbers in symbol equation tell you the amount of moles for each reactant and product
• if there is not a big number then the mole is 1
• if you have the masses of the reactants and products you can work out the balanced symbol equation
• 1) mass/RAM for each substance to find moles
• 2) Mole / smallest mole in reaction
• 3) make them all whole numbers if any are decimals
• 4) write out the balanced equation using the whole numbers neatly
• Conservation of Mass
• in a closed chemical reaction the mass of the products is equal to the mass of the reactants
• atoms cannot be created or destroyed
• this is the reason we balance equations
• if the mass changes in an open chemical reaction a gas is usually release, causing it to seem like the mass has decreased or increased
• Concentration of solutions
• concentration = mass of solute (g) / volume of solvent (dm3)
• it is a measure of how crowded thing are