Empirical formula and moles
By Heidi Maloy
Created 3 years ago
How to find an empirical formula using grams and moles
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Slide 1 - How to work with moles
- And find an empirical formula with mole information
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.
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?
Slide 4 - Problem # 3 on the worksheet
- 3. What mass of water would you need to have 15.0 moles of H2O?
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:
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
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.