(Ch.6) Chemical Composition

Question 1

What is Molar Mass?

Answer 1

The mass of one mole of a substance.

Question 2

How does one determine the molar mass of a substance?

Answer 2

Using the same method as we use to find formula mass.

(# of atoms of 1st element)(molar mass of 1st element)+ (# of atoms of 2nd element)(molar mass of 2nd element)

Question 3

How do you convert from grams to moles?
ex. .12 mol of Pb to grams
ex. .46 g of He in moles

Answer 3

You use molar mass.
ex. .12(207.2)= 25g
ex. .46 (1/4.003)= .11 moles

Question 4

How do you convert from moles to particles?

Answer 4

You use Avogadro’s Number.

Question 5

How do you find the Mass Percent of an element in a compound?

Answer 5

MP=
mass of the element/ mass of the compound (100%)

Question 6

How do you find the Mass Percent of an element in a compound?

Answer 6

You start by finding the overall mass of the compound, then find the mass percent of the element/mass of the compound as usual.

Question 7

How do you find the Empirical Formula of a compound given the percentages/grams of the elements?

Answer 7

1. Convert the mass of each element to mols.
2. Divide the mols by the smallest mols to find the subscripts of the elements.
3. If the subscripts are not whole number, multiply them (all) by a whole number to get, well, whole number subscripts for your formula.

Question 8

How do you find the Molecular Formula of a compound given the

Answer 8

1. You divide the actual molar mass of the compound by the empirical (simplified) molar mass.
2. Then you multiply the subscripts by the given value to find the molecular (actual) equation.

n= molar mass/EF molar mass