 # Chapter 10 Chemical Quantities

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Chapter 10 Chemical Quantities
Hingham High School Mr. Clune

What is a Mole? 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 (abbreviated: mol)
Defined as the number of carbon atoms in exactly 12 grams of carbon-12. 1 mole is 6.02 x particles. Treat it like a very large dozen 6.02 x is called Avogadro’s number.

Representative particles
The smallest pieces of a substance. For a molecular compound: it is the molecule. For an ionic compound: it is the formula unit (ions). For an element: it is the atom. Remember the 7 diatomic elements (made of molecules)

Types of questions 5 17 3 2 5 How many oxygen atoms in the following?
CaCO3 Al2(SO4)3 How many ions in the following? CaCl2 NaOH 5 17 3 2 5

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.

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

X = 28.10g Examples How much would 2.34 moles of carbon weigh?
1 mole of C is 12.01g or 12.01 g/mole 2.34 mole X g mole = 28.10g

X = Examples How many moles of magnesium is 24.31 g of Mg?
1 mole of Mg is 24.31g or 24.31 g/mole 1 mole 24.31 g 24.31g X = 1 mole

8.67x1022atoms Examples How many atoms of lithium is 1.00 g of Li?
6.94g/mole 6.02x1023 atoms mole 1.00g 1 mole 6.94g 6.02x1023 atoms mole X X 8.67x1022atoms

13.6g How much would 3.45 x 1022 atoms of U weigh? 238.03g/mole
6.02x1023atm 3.45x1022atm 238.03g mole X X 13.6g

What about compounds? 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? H2O 1 mole of H2O molecules has two moles of H atoms and 1 mole of O atoms

H2O What about compounds? H:2 moles X 1.08g/mole = 2.16g
O:1 mole X 16.00g/mole= g + 1 mole of H20 = g

What is the mass of one mole of CH4?
What about compounds? What is the mass of one mole of CH4? 1 mole of C x g = 12.02g 4 mole of H x g = g + 1 mole CH4 = 16.05g

What about compounds? The Molar Mass of CH4 is 16.05g
this is the mass of one mole of a molecular compound.

Moles to Mass Conversions
How many grams of Na are there in 1.23 moles? 1. How many grams of Na are there in 1 mole? 22.99g/mol 2. How many grams of Na are there in 1.23 moles? 1.23 mol g mol X 28.28g =

Moles to Mass Conversions
How many grams of C6H12O6 are there in 0.56 moles? 1. How many grams of C6H12O6 are there in 1 mole? C: 6 x 12.01g = g H: 12 x 1.01g = g O: 6 x 16.00g = g + 180.18g/mol

Moles to Mass Conversions
2. How many grams of C6H12O6 are there in 0.56 moles? 0.56mol g mol X 28.28g =

Representative Particles
Moles How many moles of water is 5.87 x molecules? 1 mole 6.02 x 1023molecules 5.87 x 1022molecules X = 0.098 moles or 9.8 x 10-2 moles

How many molecules of CO2 are there in 4.56 moles of CO2 ?
6.02 x 1023molecules 1 mol 4.56 mol = X 2.75 x 1024 molecules

How many atoms of carbon are there in 1.23 moles of C6H12O6 ?
6.02 x 1023molecules 1 mol 1.23 mol = X 7.40 x 1023molecule 6 atoms of C 1 molecule X = 4.44 x 1024 atoms of C

How many moles is 7.78 x 1024 formula units of MgCl2?
6.02 x 1023molecules 7.78 x 1024molecules X = 12.92 moles

5.00 moles What is the weight of 3.01 x 1024 molecules of NaOH?
1. Find the number of moles. 1 mole 6.02 x 1023molecules 3.01 x 1024molecules X = 5.00 moles

2. Find the mass of one mole
of NaOH. Na : 1 x = 22.99g O : 1 x = 16.00g H : 1 x = g + 40.07g

3. Find the mass of 5 moles of NaOH. 40.07g 1 mol 200.35g 5 mol = X

Practice Problems Worksheet
Homework 10-1 Practice Problems Worksheet 1-16 Due: 01/10/05

Molar Mass Molar mass is the generic term for the mass of one mole of any substance (in grams) The same as: 1) gram molecular mass, 2) gram formula mass, and 3) gram atomic mass- just a much broader term.

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

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 = 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 = g 1 mole of H = 1.01 g 1 mole NaOH = 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 = g 1 mole of H = 1.01 g 1 mole NaOH = 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 = g 1 mole of H = 1.01 g 1 mole NaOH = g

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 We need to compare them at the same temperature 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 1 mole = 22.4 L of any gas at STP

Examples What is the volume of 4.59 mole of CO2 gas at STP? 4.59 mol 22.4 L 1 mol X = L

How many moles is 5.67 L of O2 at STP?
Examples How many moles is L of O2 at STP? 5.67 L 1 mol 22.4 L X = 0.25 mol

0.55 mol What is the volume of 8.8 g of CH4 gas at STP?
1. Find the molar mass of CH4. C: 1 X = 12.01g H: 4 X = g + 16.05g 2. Find the number of moles. 8.8g 1 mol 16.05g = 0.55 mol X

What is the volume of 8.8 g of CH4 gas at STP?
3. Find the volume of CH4. 22.4 L 1 mol 0.55 mol X = 12.32 L

Mole Volume Mass Particle 22.4L 1 mol 22.4L 1 mol molar mass
6.02X1023part. 1 mol Mole molar mass 1 mol 6.02X1023part. 1 mol 1 mol molar mass Mass Particle

Homework Finish worksheet. Due: 1/11/05 Quiz on Conversions

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, then the mass is the molar mass (from 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 1 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 g/L? 2.86 g/L?

Summary These four items are all equal: a) 1 mole
b) molar mass (in grams) c) 6.02 x 1023 representative particles d) 22.4 L at STP Thus, we can make conversion factors from them.

Section 10.3 Percent Composition and Chemical Formulas
OBJECTIVES: Calculate the percent composition of a substance from its chemical formula or experimental data.

Section 10.3 Percent Composition and Chemical Formulas
OBJECTIVES: Derive the empirical formula and the molecular formula of a compound from experimental data.

Calculating Percent Composition of a Compound
Like all percent problems: Part X 100% whole Find the mass of each component, Then divide by the total mass.

1. Calculate the total mass.
Example Calculate the percent composition of a compound that is g of Ag with 4.30 g of S. 1. Calculate the total mass. Ag + S = 29.00g g = 33.30g

2. Calculate % of each element.
Example 2. Calculate % of each element. 29.00g 33.3g X 100% = 87% Ag 4.30g 33.3g X 100% = 13% S

Getting it from the formula
If we know the formula, assume you have 1 mole. Then you know the mass of the pieces and the whole. Find the Molar Mass.

Calculate the percent composition of C2H4.
Examples Calculate the percent composition of C2H4. C: 2 x 12.0 = 24.0g H: 4 x = g + Total Mass = 28.0g

2. Calculate % of each element.
Example 2. Calculate % of each element. 24.0g 28.0g X 100% = 86% C 4.0g 28.0g X 100% = 14% H

C: 0.85g X .75 =0.64g O: 0.85g X .25 =0.21g Examples
If a substance which has a mass of 0.85g is 75% C and 25% 0, how much of each substance is there? C: 0.85g X .75 =0.64g O: 0.85g X .25 =0.21g

Show all work in Notebook!!!!
Homework Worksheet 10-3 1-9 Show all work in Notebook!!!! Due: 2/01/06 Quiz: 2/2/06

The Empirical Formula The lowest whole number ratio of elements in a compound. The molecular formula = the actual ratio of elements in a compound. The two can be the same.

CH2 is an empirical formula C2H4 is a molecular formula
The Empirical Formula CH2 is an empirical formula C2H4 is a molecular formula C3H6 is a molecular formula H2O is both empirical & molecular

Calculating Empirical
Just find the lowest whole number ratio C6H12O6 CH4N - CH2O - CH4N

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

Calculate the empirical formula of a compound composed of 38
Calculate the empirical formula of a compound composed of % C, % H, and %N. Assume 100 g so: C: 38.67g x 1mol = 3.22 mol C 12.0g H g x 1mol = mol H g N: 45.11g x 1mol = 3.22 mol N g

The Smallest number is 3.22mol. Divide each mole value by 3.22mol.

The ratio of C:N 3.22 mol C = 1 mol C 3.22 mol N mol N The ratio H:N 16.09 mol H = 5 mol H 3.22 mol N mol N C1H5N1

A compound is 43.64 % P and 56.36 % O. What is the empirical formula?
Assume 100g & find moles. P: 43.64g 1mol 30.97g X = 1.41 mol O: 56.36g 1mol 16.00g X = 3.52 mol

Ratio of P:O P2O5 Find ratio of moles. 1.41 mol of P 3.52 mol of O
= P2O5 Empirical Formula

Example Caffeine is 49.48% C, 5.15% H, 28.87% N and 16.49% O. What is its empirical formula? Assume 100g & find moles.

C: H: N: O: 49.48g 1mol 12.0g X = 4.12 mol 5.15g 1mol 1.0g X =

Ratio of C:H:N:O Find ratio of moles. 4.12 mol of C 1.03 mol of O
= 5.10 mol of H 1.03 mol of O 5 of H 1 of O = 2.06 mol of N 1.03 mol of O 2 of N 1 of O =

Ratio of C:H:N:O 4:5:2:1 C4H5N2O Find ratio of moles.
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 empirical formula mass. Caffeine has a molar mass of 194 g. what is its molecular formula?

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

Cl: C: H: Assume 100g & find moles. 71.65g 1mol 35.45g X = 2.02 mol

Ratio of Cl:C:H CH2Cl Find ratio of moles. 2.02 mol of Cl
= 4.03 mol of H 2 of H 1 of C = 2.02 mol of C CH2Cl Empirical Formula

Find the mass of the empirical formula.
CH2Cl C: 1 X g = g H: 2 X g = g Cl: 1 X g = g + 49.48g

Compare to the molar mass of the molecular formula.
49.48g for CH2Cl Empirical Formula 98.96g for Molecular Formula C2H4Cl2

Homework Worksheet 10-3 10 – 25 Due: 2/2/06 Quiz: 2/2/06

Homework Worksheet 10-3 Finish Due: 1/18/05 Test: 1/18/05