FORMULA MASS, MOLECULAR MASS, & PERCENT COMPOSITION

FORMULA MASS

The total mass of an ionic compound

Sum of the masses of all atomsRemember- subscripts tell how many

of each atom is in the compound!Ex: NaCl= (1 x 22.990 amu)+ (1 x

35.453 amu)= 58.443 amu

MOLECULAR MASS

Mass of a molecular compoundProcess for calculating molecular

mass is the same as for ionic compounds

Ex: H2O= (2 x 1.008 amu) + (1 x 15.999 amu) = 18.015 amu

PRACTICE

Determine the mass of the following compounds:

CO2 MgCl2 KI BH3

PERCENT COMPOSITION

Percentage by mass of each element in a compound

Mass of element x 100 = % composition of mass of compound element

EXAMPLE

% composition of O in CO2:CO2 = (1 x 12.01 amu) + (2 x

16.00 amu)= 44.01 amu2 O atoms in CO2, which weigh a

total of 32.00 amu (16.00 x 2)32.00 amu x 100 = 72.71%

44.01 amu

PRACTICE

What is the percent composition of H in H2O?

What is the percent composition of Li in Li2O?

Chemical Equations and Reactions

What is a chemical reaction?

• process by which one or more substances are changed into one or more different substances

• Two parts: reactants and products• Described by chemical equations

– Provide symbols, identities, and amounts of each substance

Indicators that a reaction occured

• Production of heat and/or light• Production of a gas• Formation of a precipitate• Color change

Symbol Meaning

“Yields”; indicates result of reaction

Reaction is reversible

(s)A reactant or product in the solid state; also

used to indicate a precipitate

Indicates a precipitate

(l) A reactant or product in the liquid state

(aq)A reactant or product in an aqueous solution

(dissolved in water)

(g) A reactant or product in the gaseous state

Indicates a gaseous product

Δ or heat Reactants are heated

2atm Pressure at which reaction is carried out

pressurePressure at which reaction is carried outexceeds normal atmospheric pressure

0°C Temperature at which reaction is carried out

MnO2

Formula of catalyst used to alter the rate of the reaction

Type of Reaction Definition General Formula Example Equation

Synthesis(composition)

Two or more substances combine to form a new

compoundA + B AB Na(s) + Cl(g) NaCl(s)

DecompositionA reactant decomposes

to form two more products

AB A + B 2H2O(l) electricity 2H2(g) + O2(g)

Single Replacement (Single Displacement)

One element replaces another element in a

compound

A + BC AC + B (metal replacing another metal)X + BY Y + BX

(nonmetal replacing another nonmetal)

Mg(s) + 2HCl(aq) → H2(g) + MgCl2(aq)

Cl2(g) + 2KBr(aq) → 2KCl(aq) + Br2(l)

Double Replacement (Double displacment)

Ions from two compounds switch

places in an aqueous solution to form new

compounds

AB + CD AC + BD2KI(aq) + Pb(NO3)2(aq) →

PbI2(s) + 2KNO3(aq)

CombustionHydrocarbon combines

with oxygen to form carbon dioxide and

water

CxHy + O2(g) __CO2(g) + H2O(l)

C3H8 + 5O2(g) 3CO2(g) + 4H2O(l)

Turn to page 271 in Textbook

Complete problems 25,26,27,28, and 29

Due TODAY! TURN IN WITH SUB.

BELL RINGER 10 Match the equation with the type of reaction.

1. Na3PO4 + 3 KOH 3 NaOH + K3PO4

2. C6H12 + 9 O2 6 CO2 + 6 H2O

3. CaCO3 CaO + CO2

4. Pb + FeSO4 PbSO4 + Fe

5. P4 + 3 O2 2 P2O3