chemistry

# Empirical formula and moles

Created 3 years ago

Duration 0:11:38
201
How to find an empirical formula using grams and moles
Slide Content
Tags: chemistry
1. ### Slide 1 - How to work with moles

• And find an empirical formula with mole information
2. ### Slide 2 - Class recap leading to solving Problem 3 on the worksheet Moles and empirical formulas

• OK so in class today for those of you who were at school we looked at the relationship between moles and grams and the # of things in a mole.
3. ### Slide 3 - Dimensional Analysis

• Dimensional analysis is focused on units. You are looking for an answer in a specific unit and you use conversion factors to allow you to get to the desired unit.
• For example…how many atoms are in 10 grams of FE?
4. ### Slide 4 - Problem # 3 on the worksheet

• 3. What mass of water would you need to have 15.0 moles of H2O?
5. ### Slide 5 - OK applying this mole knowledge to empirical formulas

• An empirical formula is the simplest formula that a compound can have. Not all formulas are empirical in nature, formulas are molecular and we will get to those later.
• The subscript ratio of any empirical formula is the based on the relative mole ratio between the elements in the compound.
• Let’s look at problem # 4 to see what this means:
6. ### Slide 6 - Problem #4

• A compound was analyzed and found to contain 9.8 g of nitrogen, 0.70 g of hydrogen, and 33.6 g of oxygen. What is the empirical formula of the compound?
• Step 1 – find the # of moles of each element
• Step 2 – find the relative mole ratio
• Step 3 – write the empirical formula
7. ### Slide 7 - Recap what do I need to know to do to find and empirical formula

• 1. Find the # of moles of each element in the formula by dividing the mass of the element by its AMU.
• 2. Divide all element moles by the element with the smallest # of moles.
• 3. Round to the nearest whole number (unless the number is close to a .5)
• The relative mole ratio becomes the subscripts of your compound.