Unit 6 Section 1 – Measuring Matter, and the Mole Section 2 – Mass and Moles, Moles and Compounds, and Percent Composition of a Compound Section 3 – Empirical and Molecular Formulas

1.To understand the concept of average mass 2.To learn how counting can be done by weighing 3.To understand atomic mass and learn how it is determined 4.To understand the mole concept and Avogadro’s number 5.To learn to convert among moles, mass, and number of atoms Objectives Section 1 – Measuring Matter, and The Mole

You could measure the amount of sand in a sand sculpture by counting each grain of sand, but it would be much easier to weigh the sand. You’ll discover how chemists measure the amount of a substance using a unit called a mole, which relates the number of particles to the mass.

Counting by Weighing Objects do not need to have identical masses to be counted by weighing. – All we need to know is the average mass of the objects. To count the atoms in a sample of a given element by weighing we must know the mass of the sample and the average mass for that element.

Counting by Weighing Averaging the Mass of Similar Objects Example: What is the mass of 1000 jelly beans? 1.Not all jelly beans have the same mass. 2.Suppose we weigh 10 jelly beans and find: 3.Now we can find he average mass of a bean. 4.Finally we can multiply to find the mass of 1000 beans!

You want to pick up some candy for your little cousins. Grace likes mints and Billy likes jelly beans. You scoop out 500 g of jelly beans but You want to make sure to get the same number of candies for each cousin. How do you do quickly obtain your mints? – Jelly beans ave. mass = 5 g – Mints ave. mass = 15 g

Two samples containing different types of components, A and B, both contain the same number of components if the ratio of the sample masses is the same as the ratio of the masses of the individual components A & B

Atomic Masses: Counting Atoms by Weighing Atoms have very tiny masses so scientists made a unit to avoid using very small numbers. 1 atomic mass unit (amu) = 1.66  g The average atomic mass for an element is the weighted average of the masses of all the isotopes of an element.

What is the mass (in amu) of 50 Carbon atoms? How many sodium atoms are present in a sample with a mass of amu?

The Mole One mole of anything contains x units of that substance. – Avogadro’s number is x A sample of an element with a mass equal to that element’s average atomic mass (expressed in g) contains one mole of atoms.

The Mole

6.02 x = Avogadro’s number – The number of representative particles in one mole of a pure substance – Representative particle = Formula unit (ionic compounds) Molecule (covalent compounds) Atom

Fe = 6.02 x atoms H 2 O = 6.02 x molecules CaCl 2 = 6.02 x formula units

Conversion Factors 6.02 x particles 1 mole 6.02 x particles

How many atoms of argon are in 2.00 mol of argon How many moles are in 4.35 x molecules of dinitrogen triflouride?

How many atoms of aluminum are in 10.0 g of aluminum?

1.To understand the definition of molar mass 2.To learn to convert between moles and mass 3.To learn to calculate the mass percent of an element in a compound Objectives Section 2 – Mass and Moles, Moles and Compounds, and Percent Composition of a Compound

A compound is a collection of atoms bound together

How many H atoms are in one molecule of glucose, C 6 H 12 O 6 ? How many H atoms are in 5 moles of glucose?

Molar Mass A compound is a collection of atoms bound together. The molar mass of a compound is obtained by summing the masses of the component atoms.

Molar Mass For compounds containing ions the molar mass is obtained by summing the masses of the component ions.

Calculating molar mass What is the molar mass of barium acetate? What is the molar mass of ammonium sulfate?

What is the mass, in grams, of 4.86 mol of CaCO 3

How many moles of juglone (C 10 H 6 O 3 ) are in 1.56 g of juglone?

Bees release 1 x 10-6 g of Isopently acetate (C 7 H 14 O 2 ) when they sting, how many molecules of isopentyl acetate are released in a typical bee sting?

Molar Volume STP – Standard temperature and pressure – T = 0 o C – P = 1 atmosphere (atm)

At STP 1 mole of gas occupies a volume of 22.4L 22.4L = molar volume of a gas 22.4L of a gas contains 6.02 x particles of that gas.

What is the volume, in L, of 1.50 mol of nitrogen at STP? How many moles of hydrogen gas are in 75.4 L of hydrogen gas?

Conversion between volume, mass, and representative particles

What is the volume of 24.8 g of oxygen gas at STP?

Percent Composition of Compounds Percent composition consists of the mass percent of each element in a compound: Mass percent =

Calculating percent composition 1.Find the total molar mass of each element in the compound. 2.Find the molar mass of the entire compound. 3.Divide the total molar mass of each element by the molar mass of the compound then multiply by Check that all your percentages add up to 100

Example: C 3 F 6 1.Total mass of C = total mass of F = 2.Mass of compound C 3 F 6 = 3.% of C = % of F = 4.Check your work!

What is the mass percent of carbon in C 10 H 14 O?

1.To understand the meaning of empirical formula 2.To learn to calculate empirical formulas 3.To learn to calculate the molecular formula of a compound Objectives Section 3 – Empirical and Molecular Formulas

Empirical Formulas The empirical formula of a compound is the simplest whole number ratio of the atoms present in the compound. – What is the empirical formula of C 6 H 12 O 6 ? The empirical formula can be found from the percent composition of the compound.

Calculation of Empirical Formulas

A compound has the composition of 65.02% Pt, 9.34% N, 2.02% H, 23.63% Cl, what is its empirical formula?

When a g sample of vanadium metal is heated in air, it reacts with oxygen to reach a final mass of g. Calculate the empirical formula of this vanadium oxide

Calculation of Molecular Formulas The molecular formula is the exact formula of the molecules present in a substance. The molecular formula is always an integer multiple of the empirical formula. Molecular formula = (empirical formula) n where n is a whole number n = molar mass of compound empirical formula mass

A powder is analyzed and found to have an empirical formula of P 2 O 5. The compound has a molar mass of g/mol. what is the compounds molecular formula?