Chapter 6 Chemical composition

6.1 The Mole SI unit, measures the amount of substance 602,213,670,000,000,000,000,000 A mole of pennies would be $6,022,136,700,000,000,000,000 six sextillion, twenty-two quintillion, one hundred thirty-six quadrillion, seven hundred trillion dollars 6.022 x 1023

6.02 x 1023 = 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

1 mole Fe = 6.02 x 1023 atoms I mole H2O = 6.02 x 1023 molecules 1 mole CaCl2 = 6.02 x 1023 formula units

How many atoms of argon are in 2.00 mol of argon How many moles are in 4.35 x 1024 molecules of dinitrogen triflouride?

Counting by weighing Atoms are too small to count individually so we count them by weighing 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.

Objects do not need to have identical masses to be counted by weighing as long as the average mass of the object is known For the purposes of counting, objects behave as though they were all identical

You want to pick up some candy for your little cousins 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 10-24 g Remember: 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 1172.49 amu?

Molar mass Mass of one mole of a substance g/mol A sample of an element with a mass equal to that element’s average atomic mass (expressed in g) contains 6.02 x 1023 atoms.

Mass of atoms is found on the periodic table K = Mass of compounds must be calculated H20 CO2

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 CaCO3

How many moles of juglone (C10H6O3) are in 1.56 g of juglone?

Bees release 1 x 10-6 g of Isopently acetate (C7H14O2) 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 oC 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 1023 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 The map shows the conversion factors needed to convert among volume, mass, and number of particles. Interpreting Diagrams How many conversion factors are needed to convert from the mass of a gas to the volume of a gas at STP?

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

Percent Composition The percent by mass of all the elements in a compound Mass % =

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

What is the percent composition of each element in Ca(NO3)2?

6.2 Empirical and Molecular formulas Empirical formula = the simplest whole number ratio of the atoms present in the compound. What is the empirical formula for the following: H2O2 C12H4Cl4O2 H2SO4

Empirical formula can be found from the percent composition of the compound

A compound has the composition of 65. 02% Pt, 9. 34% N, 2. 02% H, 23 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 0.3546 g sample of vanadium metal is heated in air, it reacts with oxygen to reach a final mass of 0.6330 g. Calculate the empirical formula of this vanadium oxide

Molecular formula = the actual formula of a compound giving the number and type of each atom in the compound. 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 P2O5 A powder is analyzed and found to have an empirical formula of P2O5. The compound has a molar mass of 283.88 g/mol. what is the compound’s molecular formula?

A compound consists of 65. 45% C, 5. 492% H, and 29 A compound consists of 65.45% C, 5.492% H, and 29.06% O by mass, and has a molar mass of 110 g/mol. Determine the empirical formula and the molecular formula.