Chemical Quantities Chemistry Tracy Bonza Sequoyah High School Chapter 11 Chemical Quantities Chemistry Tracy Bonza Sequoyah High School

How do you measure how much? You can measure mass, or volume, or you can count pieces. We measure mass in grams. We measure volume in liters. We count pieces in MOLES.

Moles Defined as the number of carbon atoms in exactly 12 grams of carbon-12. 1 mole is 6.02 x 1023 particles. Treat it like a very large dozen 6.02 x 1023 is called Avogadro's number.

Measuring Moles Remember relative atomic mass? The amu was one twelfth the mass of a carbon 12 atom. Since the mole is the number of atoms in 12 grams of carbon-12, the decimal number on the periodic table is also the mass of 1 mole of those atoms in grams.

Representative particles How many oxygen atoms in the following? CaCO3 Al2(SO4)3 How many ions in the following? CaCl2 NaOH

Molar Mass The mass of 1 mole of an element in grams. 12.01 grams of carbon has the same number of pieces as 1.008 grams of hydrogen and 55.85 grams of iron. We can write this as 12.01 g C = 1 mole We can count things by weighing them.

What is the molar mass of: Potassium Zinc Neon 39g 65.4g 20.2g What does that mean? It means that 39g of K is 1 mole of potassium How many particles of potassium is that? 6.02 x 10 23 See…….we can count particles without counting them ……….we weighed them!!!

What about compounds? in 1 mole of H2O molecules there are two moles of H atoms and 1 mole of O atoms To find the mass of one mole of a compound determine the moles of the elements they have Find out how much they would weigh add them up

What about compounds? What is the mass of one mole of CH4? 1 mole of C = 12.01 g 4 mole of H x 1.01 g = 4.04g 1 mole CH4 = 12.01 + 4.04 = 16.05g The Molar mass of CH4 is 16.05g The mass of one mole of a molecular compound.

Molar Mass The generic term for the mass of one mole. The same as gram molecular mass (for molecules/covalent compounds), gram formula mass (for formula units/ionic compounds), and gram atomic mass (for atoms). I will use the generic molar mass (sometimes I slip up and call it gram formula mass so work with me here!!!!!)

Examples Calculate the molar mass of the following and tell me what type it is. Na2S N2O4 C Ca(NO3)2 C6H12O6 (NH4)3PO4

Finding moles of compounds Counting pieces by weighing Using Molar Mass Finding moles of compounds Counting pieces by weighing

Molar Mass The number of grams of 1 mole of atoms, ions, or molecules. We can make conversion factors from these. To change grams of a compound to moles of a compound.

For example How many moles is 5.69 g of NaOH?

For example How many moles is 5.69 g of NaOH?

For example How many moles is 5.69 g of NaOH? need to change grams to moles

For example How many moles is 5.69 g of NaOH? need to change grams to moles for NaOH

For example How many moles is 5.69 g of NaOH? need to change grams to moles for NaOH 1mole Na = 22.99g 1 mol O = 16.00 g 1 mole of H = 1.01 g

For example How many moles is 5.69 g of NaOH? need to change grams to moles for NaOH 1mole Na = 22.99g 1 mol O = 16.00 g 1 mole of H = 1.01 g 1 mole NaOH = 40.00 g

For example How many moles is 5.69 g of NaOH? need to change grams to moles for NaOH 1mole Na = 22.99g 1 mol O = 16.00 g 1 mole of H = 1.01 g 1 mole NaOH = 40.00 g

For example How many moles is 5.69 g of NaOH? need to change grams to moles for NaOH 1mole Na = 22.99g 1 mol O = 16.00 g 1 mole of H = 1.01 g 1 mole NaOH = 40.00 g

Examples How much would 2.34 moles of carbon weigh, in grams? How many moles of magnesium in 24.31 g of Mg? How many moles is 4.56 g of CO2 ? How many grams is 9.87 moles of H2O?

Moles and Molecules 6.02 x 1023 =1 mole too! So we can convert from moles to molecules too! Try it: How many molecules are there in 3.6 moles of sodium hydroxide? How many moles is 3.6x 1034 molecules of gold?

3 Step Problems Converting from grams to molecules/atoms and molecules/atoms to grams How many atoms of silver are in 2.3g of silver?

Examples How many molecules in 6.8 g of CH4? 49 molecules of C6H12O6 weighs how much? How many atoms of lithium in 1.00 g of Li? How much would 3.45 x 1022 atoms of U weigh?

Gases and the Mole

Gases Many of the chemicals we deal with are gases. They are difficult to weigh. Need to know how many moles of gas we have. Two things effect the volume of a gas Temperature and pressure Compare at the same temp. and pressure.

Standard Temperature and Pressure 0ºC and 1 atm pressure abbreviated STP At STP 1 mole of gas occupies 22.4 L Called the molar volume Avogadro’s Hypothesis - at the same temperature and pressure equal volumes of gas have the same number of particles.

Examples What is the volume of 4.59 mole of CO2 gas at STP? How many moles is 5.67 L of O2 at STP? What is the volume of 8.8g of CH4 gas at STP?

Density of a gas D = m /V for a gas the units will be g / L We can determine the density of any gas at STP if we know its formula. To find the density we need the mass and the volume. If you assume you have 1 mole than the mass is the molar mass (PT) At STP the volume is 22.4 L.

Examples Find the density of CO2 at STP. Find the density of CH4 at STP.

The other way Given the density, we can find the molar mass of the gas. Again, pretend you have a mole at STP, so V = 22.4 L. m = D x V m is the mass of 1 mole, since you have 22.4 L of the stuff. What is the molar mass of a gas with a density of 1.964 g/L? 2.86 g/L?

All the things we can change

We have learned how to change moles to grams moles to atoms moles to formula units moles to molecules moles to liters molecules to atoms formula units to atoms formula units to ions

Mass Moles

Mass ?g Moles

Mass Volume ?g Moles

Mass Volume 22.4 L ?g Moles

Mass Volume 22.4 L ?g Moles Representative Particles

Mass Volume 22.4 L ?g Moles 6.02 x 1023 Representative Particles

Mass Volume 22.4 L ?g Moles 6.02 x 1023 Representative Particles Atoms

Mass Volume Moles 6.02 x 1023 Representative Particles molecules Atoms ?g Moles 6.02 x 1023 Representative Particles molecules Atoms

Percent Composition Like all percents Part x 100 % whole Find the mass of each component, divide by the total mass.

Example Calculate the percent composition of a compound that is 29.0 g of Ag with 4.30 g of S.

Getting it from the formula If we know the formula, assume you have 1 mole. Then you know the pieces and the whole.

Examples Calculate the percent composition of C2H4? Aluminum carbonate.

From percentage to formula Empirical Formula From percentage to formula

The Empirical Formula The lowest whole number ratio of elements in a compound. The molecular formula the actual ration of elements in a compound. The two can be the same. CH2 empirical formula C2H4 molecular formula C3H6 molecular formula H2O both

Calculating Empirical Just find the lowest whole number ratio C6H12O6 CH4N It is not just the ratio of atoms, it is also the ratio of moles of atoms. In 1 mole of CO2 there is 1 mole of carbon and 2 moles of oxygen. In one molecule of CO2 there is 1 atom of C and 2 atoms of O.

Calculating Empirical Means we can get ratio from percent composition. Assume you have a 100 g. The percentages become grams. Can turn grams to moles. Find lowest whole number ratio by dividing by the smallest.

Example Calculate the empirical formula of a compound composed of 38.67 % C, 16.22 % H, and 45.11 %N. Assume 100 g so 38.67 g C x 1mol C = 3.220 mole C 12.01 gC 16.22 g H x 1mol H = 16.09 mole H 1.01 gH 45.11 g N x 1mol N = 3.219 mole N 14.01 gN

Example The ratio is 3.220 mol C = 1 mol C 3.219 molN 1 mol N The ratio is 16.09 mol H = 5 mol H 3.219 molN 1 mol N C1H5N1 A compound is 43.64 % P and 56.36 % O. What is the empirical formula? Caffeine is 49.48% C, 5.15% H, 28.87% N and 16.49% O. What is its empirical formula?

Empirical to molecular Since the empirical formula is the lowest ratio the actual molecule would weigh more. By a whole number multiple. Divide the actual molar mass by the the mass of one mole of the empirical formula. Caffeine has a molar mass of 194 g. what is its molecular mass?

Example A compound is known to be composed of 71.65 % Cl, 24.27% C and 4.07% H. Its molar mas is known (from gas density) is known to be 98.96 g. What is its molecular formula?