MOLES, MOLAR MASS, PERCENT COMPOSITION AND STOICHIOMETRY

Question 1

What is a mole?

Answer 1

A way to count up all of the atoms in matter
Number of things equal to the number of atoms in exactly 12g of carbon-12

1 mol = 6.022x10^23 (Avogadro’s number)

Question 2

How do you calculate molar mass?

Answer 2

1. Write the formula of the compound (use empirical formula for ionic, molecular for covalent)
2. calculate the formula/molecular mass in amu’s (Da or amu)
3. Change the units to g/mol

Molar mass is equal to the formula and molecular mass

Question 3

How do you find the percent composition of elements in a compound

Answer 3

1. Find the molar mass of all elements in the compound
2. Find the molecular mass of the entire compound (sum of molar mass)
3. Divide the components molar mass by the entire molecular mass
4. You will now have a number between 1 and 0. Multiply it by 100% to get the percent composition

Question 4

How do you use the percent composition to determine the empirical and molecular formula

Answer 4

1. Calculate the number of moles of each element within a molecule of a given mass
2. find the simplest whole number ratio of the elements (empirical formula)
3. Determine the molecular formula

Question 5

What is stoichiometry?

Answer 5

A balanced equation shows the stoichiometry between reactants and products, stoichiometric coefficient is the number before the atom, it helps to identify the mole ratio

Question 6

What is a hydrated salt?

Answer 6

Ionic compounds can have water attached to them in their crystalline structure, the formula mass needs to include the water

Question 7

Describe standard temperature and pressure

Answer 7

At 0c and 100kPa (1atm) every single gas will have 1 mole of molecules in 22.4L

At 25c and 100kPa (1atm) every single gas will have 1 mol of molecules in 24.79L

Question 8

How do you calculate:

1. moles
2. mass
3. Molar mass

Answer 8

1. n= m/M
2. m = n x M
3. M = m/n

Question 9

Define:

1. Limiting Reagent

2. Excess reagent

Answer 9

1. The reactant that gets consumed first in a chemical reaction and therefore limits how much product can be formed
2. Reactants that are not used up when the reaction is finished are called excess reagents

Question 10

What is theoretical yield and how is it calculated?

Answer 10

Theoretical yield is the max product yield expected based on masses of reactant and reaction stoichiometry

1. Determine the mole ratios between the reactants and the product
2. Use molar mass of reactant to convert grams of reactant to moles of reactant
3. Use the mole ratio between reactant and product to convert moles reactant to moles product
4. Use the molar mass of the product to convert moles product to grams of product

Question 11

What is actual yield and how is it calculated?

Answer 11

The experimentally measured amount of products that result upon completion of reaction
Actual yield is simply determined by weighing the product

Question 12

What is percentage yield and how is it calculated?

Answer 12

Percentage yield is the measure of the extent of the reaction in terms of actual vs theoretical yield

% yield = actual yield / theoretical yield x100