Mass:≈ 1.66 × 10 −27 to 4.52 × 10 −25 kg  The mole is a measure of the amount of a substance.  Abbreviated mol  Amount of substance which contains.

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Presentation transcript:

Mass:≈ 1.66 × 10 −27 to 4.52 × 10 −25 kg

 The mole is a measure of the amount of a substance.  Abbreviated mol  Amount of substance which contains as many particles as there are atoms in exactly 12 g of 12 C.  Avogadro’s number = 6.02 x 10 23

A mole of dollars was created at the time the earth was formed, approximately 4.5 billion years ago. It was given away at the rate of exactly 1 million dollars per second since that time. Did the money run out?

Mole conversions: To calculate the number of atoms (molecules, formula units in a given number of moles, multiply by Avogadro’s number. To calculate the number of moles in a given number of atoms (molecules, formula units) divide by Avogadro’s number.

 Mathematically defined as the mass of the substance divided by its molar mass.  Molar mass = the sum of the weights of each of the atoms in the compound. Ex. NaCl = = g  Determine the molar mass of: CO 2, NH 3, sodium sulfate, barium chloride.

How Big Is A Mole? If someone had a mole of pennies and wanted to buy kite string at a million dollars/in 2, they would have enough string to loop around the earth 3 million times and go from the earth to the moon 25000X.

Calculate the number of moles in the following: 5.46 g calcium nitrate 3.99 g aluminum hydroxide 15.5 g magnesium phosphide

 Percentage Composition  Empirical Formulas  Molecular Formulas

 The percentage by mass contributed by each element in the substance.  Often used to verify the purity of a compound.  Uses formula weights from the periodic table if the formula is known.

% elem. = total weight of element formula weight of compound x 100% Calculate the percentage composition of sucrose (C 12 H 22 O 11 ): %C = (12) (12.01) %O = (11) (16) %H = (22) (1.01)

For each of the following, find the percentage composition from the analysis determined by experiment. 1.A g sample contains 3.83 g Fe and g Br. 2. A 9.14 g sample contains 4.77 g C, 1.19 g H, and 3.18 g O.

Calculate the percentage composition from the formula of the compound. Sodium iodide Calcium oxalate Aluminum Sulfate

 Indicates the relative number of atoms of each element in a compound.  It is the smallest whole number ratio of the atoms in a formula.  Gives the subscripts for the formula.

Empirical Formulas are determined from experimental results. A compound contains 40.92% C, 4.58% H, and 54.50% O. What is the empirical formula of the compound? 1.Assume a 100 gram sample so that the percentages become grams. 2. Convert the grams to moles.

3. Divide by the smallest number. 4. You may not round values that are >.2 or <.9. Multiply by some factor to make the decimal a whole number.

The formulas derived from percentage composition are always empirical formulas. The molecular formula represents the actual number of atoms in a formula. It is always a multiple of the empirical formula. CH 4 is an empirical formula; C 2 H 8 is a molecular formula. The two are related by their molar masses. CH 4 = g/mol C 2 H 8 = g/mol 32.10/16.05 = 2

The two tells you to multiply the empirical formula’s subscripts by 2. Mesitylene has an empirical formula of C 3 H 4. The molecular mass for this compound is 121 g. Determine the molecular formula for mesitylene.

Ethylene glycol, used in antifreeze, is composed of 38.7% C, 9.7% H and 51.6%O. The molar mass of ethylene glycol is 62.1 g/mol. What is the molecular formula for the compound?

Mini-Review: Empirical Formulas Some crystals have water molecules as part of their lattice; these are called hydrates. CuSO 4. 5H 2 O Analyzing these compounds requires driving off the water that is present and weighing the “anhydrous” or dry salt produced.

A 5.00 g sample of a hydrate of barium chloride is heated. The remaining salt is found to weigh 4.26 g. Determine the empirical formula of this hydrate.