Unit 6: The Mole

Note: Most of this unit will be solving problems, with many examples done in class on the board.

Recall:1 mol = !6.02x1023 particles

Recall:1 mol = !6.02x1023 particles1 mol = !the molar mass of an! ! ! ! ! ! atom or compound

Recall:1 mol = !6.02x1023 particles1 mol = !the molar mass*of an! ! ! ! ! ! atom or compound

Synonyms for molar mass:! - molecular mass! ! - formula mass! ! ! - formula weight

Section 7.3 i) Calculating molar massii) Mole-mass conversions

Page 230Percent composition:the percent by mass of each element in a compound.

Practice:What is the percent composition of water?

What is the percent composition of magnesium chloride?

Section 7.4 Determining Chemical Formulas

Empirical formula:the smallest whole-number ratio of atoms in a compound.

Practice:1. Determine the empirical formula of a ! compound composed of: ! ! ! ! 81.82% carbon! ! ! ! 18.18 % hydrogen

1. Determine the empirical formula of a compound composed of:

! ! ! ! 81.82% carbon! ! ! ! 18.18 % hydrogen! ! (assume a 100-gram sample!)

Note:If mole ratio is within +/-0.1 of a whole

number, round to that number.

If not, multiply by 2/2, 3/3, etc., to obtain a whole-number ratio.

2. Determine the empirical formula of a compound composed of:

! ! ! 68.4% chromium! ! ! 31.6% oxygen

3. Determine the empirical formula of a compound composed of:

! ! ! 26.6% sulfur! ! ! 53.2% oxygen! ! ! 20.2% magnesium

4. Determine the empirical formula of a compound composed of:

! ! ! 9.61g oxygen! ! ! 7.33g magnesium! ! ! 0.61g hydrogen?

4. Determine the empirical formula of a compound composed of: ! ! ! 9.61g oxygen! ! ! 7.33g magnesium! ! ! 0.61g hydrogen. ! ! ! What is its name?

Molecular formula: the actual number of atoms in a compound.

Molecular formula: the actual number of atoms in a compound…

Molecular formula: the actual number of atoms in a compound... It will be a whole-number multiple of the empirical formula (1, 2, etc…).

Practice 1:The empirical formula of a compound is: C3H4N2.

Practice 1:The empirical formula of a compound is: C3H4N2. What is its molecular formula if the molar mass has been determined to be 204.2 g/mol?

Practice 2:i. Determine the empirical formula of a compound composed of:! ! 40.29% boron! ! ! 7.51% hydrogen! ! ! ! 52.20% nitrogen

Practice 2:i. Determine the empirical formula of a compound composed of:! ! 40.29% boron! ! ! 7.51% hydrogen! ! ! ! 52.20% nitrogenii. If the molar mass of the compound is 80.51g, what its molecular formula?

Pages 231-232The Formula of a Hydrate

Hydrate: An ionic compound that has a specific number of water molecules bound within its crystal structure.

Hydrate: A compound that has a specific number of water molecules bound to its atoms.

Prefixes mono, di, tri, etc. are used to indicate the number of water molecules contained in the hydrate formula.

Examples

Heating

!! ! Hydrate ------->Anhydrate

Anhydrate: A hydrate that has had its water molecules removed.

Anhydrate: A hydrate that has had its water molecules removed.(aka “desiccant,” a drying agent that absorbs water from the air)

=See Dry Lab Practice Worksheet=