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**Chapter 10 Chemical Quantities**

Hingham High School Mr. Clune

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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.

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**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.

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**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)

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**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

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**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.

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**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.

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**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

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**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

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**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

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**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

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**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

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

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**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

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**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

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**What about compounds? The Molar Mass of CH4 is 16.05g**

this is the mass of one mole of a molecular compound.

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**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 =

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**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

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**Moles to Mass Conversions**

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

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**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

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**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

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**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

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**How many moles is 7.78 x 1024 formula units of MgCl2?**

6.02 x 1023molecules 7.78 x 1024molecules X = 12.92 moles

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**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

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**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

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

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**Practice Problems Worksheet**

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

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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.

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

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**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.

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For example How many moles is 5.69 g of NaOH?

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For example How many moles is 5.69 g of NaOH?

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**For example How many moles is 5.69 g of NaOH?**

need to change grams to moles

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**For example How many moles is 5.69 g of NaOH?**

need to change grams to moles for NaOH

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**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

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**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

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**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

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**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

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**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.

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**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

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

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**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

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**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

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**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

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**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

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

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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.

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

Find the density of CH4 at STP.

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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?

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**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.

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**Section 10.3 Percent Composition and Chemical Formulas**

OBJECTIVES: Calculate the percent composition of a substance from its chemical formula or experimental data.

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**Section 10.3 Percent Composition and Chemical Formulas**

OBJECTIVES: Derive the empirical formula and the molecular formula of a compound from experimental data.

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**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.

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**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

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**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

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**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.

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**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

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**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

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**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

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**Show all work in Notebook!!!!**

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

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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.

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**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

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**Calculating Empirical**

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

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**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.

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**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.

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**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

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

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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

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**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

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**Ratio of P:O P2O5 Find ratio of moles. 1.41 mol of P 3.52 mol of O**

= P2O5 Empirical Formula

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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.

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

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**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 =

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**Ratio of C:H:N:O 4:5:2:1 C4H5N2O Find ratio of moles.**

Empirical Formula

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**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?

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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?

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

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**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

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**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

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**Compare to the molar mass of the molecular formula.**

49.48g for CH2Cl Empirical Formula 98.96g for Molecular Formula C2H4Cl2

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

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

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