​Sometimes, the empirical formula is also the molecular formula ( ex. H₂O)

​How to calculate empirical formula from percent composition

In order to calculate the empirical formula of a compound we must first determine the relative masses of elements present- 

• The relative masses will give us what?

  •  the ratios of the elements present in the compound. 

• The ratios will give us what?

  •  the subscripts

• One way to find the relative masses in the compound is to measure the masses that react to form the compound

• Write this down: Percent to grams, grams to moles, divide by smallest, multiply til whole

​Percent to grams, grams to moles, divide by smallest, multiply til whole

​Percent to grams, grams to moles, divide by smallest, multiply til whole

​Try this one.....

​Percent composition lego activity (pg 27)

​Percent composition lego activity (pg 27)

Each group will receive 10 lego pieces

• 3 will be given to you

• 7 you may choose

• On the worksheet draw a rough picture or description of each DIFFERENT shaped piece you have (color does not matter, if the pieces are the same size and shape, they count as the same piece)

• Use the balance to get the mass of each different piece on your list

• Fill in your table with the mass and # of blocks for each different type

• Build a lego structure and calculate the molar mass of your structure 

• Next, calculate the percent composition of each different piece

• Once you have calculated percent comp for each piece you may build something else!

• If you finish earl​y, work on pages 28-29, or 24-25.