What is the pH of the following concentrations?

• 1.0 E -9• 2.4 E -3• 6.7 E -7• 4.4 E -5

– Classify each as Acid or Base

Stoichiometry

I didn’t know there would be math in Chemistry class!

Avogadro’s Number

• Suppose you have a sample of an element and the mass of the sample is equal to the atomic mass of the element– AKA: Avogadro’s Number (6.02 x 1023)

• Avogadro’s number of particles is called a mole of particles

Def: Mole- SI base unit used to measure the amount of a substance and is based off the number if particles in 12g of Carbon-12

What it is used to convert to

Examples

• Moles to Number of Particles– Find the number of molecules that are in 2.25

moles of Bromine (Br2)?

– Calculate the number of molecules in 15.7 mol CO2

– Calculate the number of molecules in 0.0544 mol of H2O

– Calculate the number of moles in 9.22 x 1023 atom Fe

Mass to moles examples

• Molar mass= Grams/1 mol• Calculate the mass of 6.89 mole Sb• A chemist needs 0.07 mol Se for a reaction. What mass

of Se should the chemist use?• A sample of S has a mass of 223g. How many moles of

S are in the sample?

Examples- Mass to No. of Particles

• Calculate the number of atoms in 2.00g of platinum.– gmolatoms

• How many sulfur atoms are in a metric ton (1 E 6 g) of sulfur– g mol atoms

• How many grams of Hg are in 1.19 E 23 atoms of Hg– Atoms mol grams

Avogadro’s Principle

- equal volumes of gases at the same temperature and pressure, contain equal numbers of particles

- molar volume – 1 mole of any gas at STP occupies 22.4 L

STP – standard temperature pressure is:0.00 ºC1.0 atm of pressure

1 mole 22.4 L22.4 L 1 mole

* Conversion factors for relating moles to volume

OR

Molarity (M)

the number of moles of solute dissolved per liter of solution

M = moles of solute L of solution

Measure mass of solute

(convert it to moles)

Use a volumetric flask to bring it to 1.0 L of solution

Percent Composition

- percent by mass of any element in a compound

mass of element x 100 = percent composition mass of compound

What is the percent composition of water?

H2O

% H = 2.016 g H X 100 = 11.2 % H 18.016 g H2O

% O = 15.99 g 0 X 100 = 88.8 % O 18.016 g H2O

What is Stoichiometry

• Def: the study of quantitative relationships between amount of reactants used and products formed by a chemical reaction

• Based on the Law of Conservation of Mass

– Remember… What goes in to a reaction must come out!

2Na + Cl2 2NaCl

• Use what you know about the LCM to answer the following– How much sodium is needed to produce a certain

amount of table salt?– How much chlorine is needed to produce a certain

amount of table salt?– Given a certain amount of sodium or chlorine,

how much table sale can be produced?

4NH3 + 5 O2 4NO + 6H2O

• Coefficients represent both the numbers of particle and the numbers of moles interacting in the chemical reaction.

• 4 molecules NH3 + 5 molecules O2 4 molecules NO + 6 molecules H2O

OR• 4 moles NH3 + 5 molesO2 4 moles NO + 6

moles H2O

4NH3 + 5 O2 4NO + 6H2O

• Use this to find the mass of each reactant and product.4 mol NH3 (17.03g / 1 mol NH3) = 68.12 g NH3

– Molar Mass

• Do this for the remaining reactants and products– Add the masses for the reactants and compare

that to the masses of the products

Practice ProblemsFind the molar mass of each. Remember to balance first!

• H2O2 O2 + H2O

• H2CO3 H2O + CO2

• HCl + O2 H2O + Cl2

Stoichiometric Calculations

• Mole-to-mole• Mole-to-mass• Mass-to-mass

Mole-to-mole

• How can you determine the number of moles of table salt (NaCl) produced from 0.02 moles of chlorine (Cl2)?

2Na + Cl2 2NaCl• Use the mole ratio to convert the known

number of moles of chlorine to the number of moles of table salt.

0.02 mol Cl2 (2 mol NaCl / 1 mol Cl2) = 0.04 mol NaCl

Try this…

• A piece of Magnesium burns in the presents of oxygen, forming magnesium oxide (MgO). How many moles of oxygen are needed to produce 12 moles of magnesium oxide.

Mole to mass

• The following reaction occurs in plant photosynthesis.6CO2 + 6H2O C6H12O6 + 6 O2

How many grams of glucose are produced when 24 moles of carbon dioxide react in excess water?

• mol CO2 mol C6H12O2

24 mol CO2 (1 mol C6H12O2 / 6 mol CO2) = 4 mol C6H12O2

• mol C6H12O2 gram C6H12O2

4 mol C6H12O2 (180.18 g C6H12O2/ 1 mol C6H12O2) = 721 g C6H12O2

Try this…

• Calculate the mass of NaCl produced when 5.50 mol of Na reacts in excess Cl2.

Mass to mass

How many grams of NaOH are needed to completely reacts with 50.0 g of Sulfuric acid to form Sodium Sulfate and water

2NaOH + H2SO4 Na2SO4 + 2H2OGrams of H2SO4 moles of NaOH

50g H2SO4 (1 mol H2SO4 / 98.09g H2SO4) (2 mol NaOH / 1 mol H2SO4)

= 1.02 mol NaOHMoles NaOH grams of NaOH

1.02 mol NaOH (40g NaOH / 1 mol NaOH)= 40.8 g NaOH

Try this…

• If 40g of Mg reacts with excess HCl, how many grams of MgCl2 are produced?

Mg + 2HCl MgCl2 + H2

Grams Mg moles MgCl2

40g Mg (1 mol Mg / 24.305 g Mg) (1 mol MgCl2 / 1 mol Mg)

=1.65 mol MgCl2

Moles MgCl2 grams MgCl2

1.65 mol MgCl2 (95.211 g MgCl2 / 1 mol MgCl2)

=157.1 g MgCl2