1.4.4 - Empirical and Molecular Formulas

Question 1

what is a molecular formula?

Answer 1

a chemical formula showing the actual number of atoms of each element present in a compound

Question 2

What is a empirical formula?

Answer 2

a molecular formula expressed in its simplest ratio

Question 3

How do you change a molecular formula into an empirical formula?

Answer 3

reduce the subscripts by finding lowest common multiple

Question 4

What is the difference between molecular and empirical formulas for ionic compounds?

Answer 4

nothing (already reduced)

Question 5

In essence, what does the empirical formula tell us?

Answer 5

the ratio of elements in a compound

Question 6

how do you solve a problem where percentages of elements are given for a compound and you have to find the empirical formula of the compound?

Answer 6

1. assume 100g sample and state each percentage to grams
2. determine # of moles of each element in 100g sample
3. set up a mole ratio and reduce to lowest whole # by dividing each value by the smallest of the values
4. state empirical formula with the whole numbers as the subscripts for each element

Question 7

What do you do when finding empirical formula and you divide each value by the smallest value and one of the resulting values is close to 0.5?

Answer 7

multiply everything by 2

Question 8

What do you do when finding empirical formula and you divide each value by the smallest value and one of the resulting values is close to 1/3?

Answer 8

multiply each value by 3

Question 9

What is the percent composition of an element?

Answer 9

How much of the mass of the compound is contributed by each element

Question 10

How do you find the theoretical percent compositions of elements in a compound?

Answer 10

find the total molar mass of the element and divide by the total molar mass of the compound, then multiply by 100%