Empirical and Molecular Formulas Chapter 10: Section 4

Balance the Following Compounds Ca Br Mg S Li N K S B O B (O H) Al O B I Sr F H (P O 4 )

Khan Academy Molecular and Empirical Formulas Salman Khan

Percent Composition Percent composition explains to you, how much of an element, by mass, makes up a compound.

Percent Composition If you have 100 g of a compound which contains 55 g of element “X” and 45 g of element “Y”, to find the percent by mass you use the following formula: Percent by mass = [mass of element / mass of compound] * 100

Percent Composition [55 g / 100 g] * 100 = 55 % for element X [45 g / 100 g] * 100 = 45 % for element Y

Percent Composition Water Hydrogen mass = g Oxygen mass = g Molar mass = g % Hydrogen % H = [2.016 g / g] * 100 % H = % O = [ g / g] * 100 % O =

Percent Composition Na (H C O 3 ) Na = g H = g C = g O = g Na (H C O 3 ) = g % Na = [22.99 g / g] * 100 % H = [1.008 g / g] * 100 % C = [12.01 g / g] * 100 % O = [48.00 g / g] * 100

Percent Composition % Na = % % H = % % C = % % O = % Total = 100% The total is slightly off due to round off error.

Balance the Following Compounds Answers Ca Br 2 Mg S Li 3 N K 2 S B 2 O 3 B (O H) 3 Al 2 O 3 B I 3 Sr F 2 H 3 (P O 4 )

Percent Composition Find the percent by mass for each of the following: 1. H Cl 2. H (N O 3 ) 3. S 2 (S O 4 ) 4. H 3 (P O 4 ) 5. Sodium Carbonate 6. Iron (III) Bromide 7. Aluminum Oxide Evaluate each answer… Your total should be 100% (or very close)

H Cl H g Cl g H Cl g H% = [1.008 g / g] * 100 H% = 2.84 Cl% = [ g / g] * 100 Cl% = = %

H (N O 3 ) H g N g O g Total = g H% = [1.008 / ] * 100 H% = 1.60 N% = [ / ] * 100 N% = O% = [ / ] * 100 O% = Total =

S 2 (S O 4 ) S g O g S 2 (S O 4 ) S% = [ / ] * 100 S% = O% = [ / ] * 100 O% = Total =

H 3 (P O 4 ) H g P g O g H 3 (P O 4 ) H% = [3.024 / ] * 100 H% = 3.09 P% = [ / ] * 100 P% = O% = [ / ] * 100 O% = Total =

Sodium Carbonate Na 2 (C O 3 ) Na g C g O g Na 2 (C O 3 ) Na% = [ / ] * 100 Na% = C% = [ / ] * 100 C% = O% = [ / ] * 100 O% = Total =

Iron (III) Bromide Fe Br 3 Fe g Br g Fe Br g Fe% = [55.87 / ] * 100 Fe% = Br% = [ / ] * 100 Br% = Total =

Aluminum Oxide Al 2 O 3