Chapter 7: Mole Concept and Stoichometry

How are measurements made in chemistry?

Mole

A term used to describe a quantity

Mole formula

molar mass

mass of 1 moles of a substance

molar mass formula

adding the atomic mass of each element in a compound

moles to number of particles formula

stoichiometric ratio

Ratio of reactants and products in a chemical reaction

Steps for mole calcs with equations

1. Balance equation

2. Determine number of moles known

3. Use mole ratio

4. Work out moles of unknown

5. Calculate desired value from the question.

Percentage Composition

percentage (by mass) of an element present in a compound.

Steps for percentage ccomposition

1. Write out formula of a compound

2. Work out molar mass

3. Calculate mass of element specified.

4. Calculate percentage mass

Empirical formula

simplest whole number ratio of the elements contained in a compund

Steps to find Empirical Formula

1. Write the symbol of each element

2. Write the percentage composition and convert to a mass in 100g sample.

3. Convert masses to moles

4. Divide by the smallest number obtained

5. Write the empirical formula.

Limiting Reagent

The substance that is used up first in a chemical reaction OR the reactant that is completely consumed if the reaction goes to completion. Determines the amount of product produced and it is the reagent with the least number of moles.

Excess Reagent

The substance that is left over in a chemical reaction OR the reactant that has a proportion unreacted if the reaction goes to completion.

Limiting reagent steps

1. Balance equation

2. Calculate the number of moles of both reactants

3. Compare the stoichiometric and actual mole ratio

4. Determine the limiting reagent

5. Write the relationship between the limiting reagents and UNKNOWN

6. Calculate number of moles of UKNOWN

7. Convert moles to what the question asks.