# Chapter 7 Chemical Quantities or How do you measure how much? You can measure mass, volume, or you can count pieces of a substance. We measure mass in.

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Chapter 7 Chemical Quantities or

How do you measure how much? You can measure mass, volume, or you can count pieces of a substance. We measure mass in grams. We measure volume in liters. We count pieces in MOLES. No, not that kind of mole!!!

Moles Defined as the number of carbon atoms in exactly 12 grams of carbon-12. 1 mole is 6.02 x 10 23 particles. Treat it like a very large dozen. 6.02 x 10 23 is called Avogadro's number. The units of Avogadro’s number can be whatever particle you are counting. – Examples: atoms, molecules, ions, formula units, etc… – In chemistry these are called Representative Particles

What are Representative Particles? The smallest pieces of a substance. For an element it is an atom. – Unless it is diatomic For a covalent compound it is a molecule. For an ionic compound it is a formula unit. If it has a charge, it is an ion.

How do We Use Moles? Moles are used as conversion factors. This means they are used to change units. Remember, when solving using conversion factors there are 3 questions you want to ask yourself: – What unit do you want to get rid of? – Where does it go to cancel out? – What can you change it into?

Calculation question 1 How many molecules of CO 2 are the in 4.56 moles of CO 2 ? Answer: 2.75 x 10 24 molecules of CO 2

Calculation question How many moles of water is 5.87 x 10 22 molecules of water? ANSWER: 0.0975 moles of water

Calculation question How many molecules of sugar are there in 1.23 moles of C 6 H 12 O 6 ?

Measuring Moles The atomic mass unit (amu) is 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: – The mass of the average atom in amu. This mass is equivalent to the mass of 1 mole of those atoms in grams.

Gram Atomic 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.

Examples How much would 2.34 moles of carbon weigh? 28.1 grams of C How many moles of magnesium in 4.61 g of Mg? 0.190 moles of Mg

What about compounds? In 1 mole of H 2 O 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 their mass is by using the periodic table and then add them up.

Example What is the mass of one mole of CH 4 ? 1 mole of C = 12.01 g 4 mole of H x 1.01 g = 4.04g 1 mole CH 4 = 12.01 + 4.04 = 16.05g The Gram Molecular mass of CH 4 is 16.05g

Gram Molecular Mass or GMM The mass of one mole of a molecular compound. Gram Formula Mass - The mass of one mole of an ionic compound. Calculated the same way as GMM. What is the GFM of Fe 2 O 3 ? 2 moles of Fe x 55.85 g = 111.70 g 3 moles of O x 16.00 g = 48.00 g The GFM = 111.70 g + 48.00 g = 159.70g

Molar Mass The generic term for the mass of one mole. The same as gram molecular mass, gram formula mass, and gram atomic mass. This is the term we will be using in class. I do NOT weigh that much! The balance must be lying!!!

Examples Calculate the molar mass of the following and tell me what type it is (gmm, gfm, or gam). Na 2 S N 2 O 4 C Ca(NO 3 ) 2 C 6 H 12 O 6 (NH 4 ) 3 PO 4 78.05 g/mol 92.02 g/mol 12.01 g/mol 164.10 g/mol 149.12 g/mol 180.18 g/mol

Using Molar Mass Finding moles of compounds Counting pieces by weighing

Molar Mass The number of grams in 1 mole of atoms, formula units, or molecules. We can make conversion factors from these. It will allow us to change grams of a compound to moles of a compound. Or moles to grams.

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? l need to change grams to moles

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

For example How many moles is 5.69 g of NaOH? l need to change grams to moles for NaOH l 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? l need to change grams to moles for NaOH l 1mole Na = 22.99g 1 mol O = 16.00 g 1 mole of H = 1.01 g add these together to get the molar mass – use it to convert! l 1 mole NaOH = 40.00 g

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

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

Examples How many moles is 4.56 g of CO 2 ? How many grams is 9.87 moles of H 2 O? 0.104 mol CO 2 177.86 g H 2 O

Gases and the Mole Where is my air tank?? I hope it’s filled to 22.4 L

Gases Many of the chemicals we deal with are gases. They are difficult to weigh, so we’ll measure volume. We still need to know how many moles of gas we have. Two things affect the volume of a gas: – Temperature and pressure. So we have to compare at the SAME temp. and pressure.

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

Examples What is the volume of 4.59 mole of CO 2 gas at STP? How many moles is 5.67 L of O 2 at STP? What is the volume of 8.8g of CH 4 gas at STP?

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

Volume Molecules Atoms Representative Particles Mass PT Moles 6.02 x 10 23 22.4 L Count

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 combined with 4.30 g of S.

Examples Calculate the percent composition of C 2 H 4. Aluminum carbonate.

Percent to Mass Multiply % by the total mass to find the mass of that component. How much aluminum in 450 g of aluminum carbonate?

Empirical Formula From percentage to formula

The Empirical Formula The lowest whole number ratio of elements in a compound. The molecular formula is the actual ratio of elements in a compound. The two can be the same. CH 2 empirical formula C 2 H 4 molecular formula C 3 H 6 molecular formula H 2 O both

Finding Empirical Formulas Just find the lowest whole number ratio. C 6 H 12 O 6, CH 4 N 2 It is not just the ratio of atoms, it is also the ratio of moles of atoms. Calculating Empirical Formulas We can get ratio from percent composition. Assume you have 100 g. The percentages become grams. Convert grams to moles. Find lowest whole number ratio by dividing everything by the smallest moles.

Example Calculate the empirical formula of a compound composed of 38.67 % C, 16.22 % H, and 45.11 %N. Assume 100 g so: = 3.22 mole C = 16.1 mole H = 3.22 mole N

Example Continued: The smallest number of moles is 3.22 mol so divide your answers by 3.22 to get the mole ratio for the formula. The ratio is:    So the formula is: C1H5N1C1H5N1

Additional Examples: A compound is 73.9 % Hg and 26.1 % Cl. 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? HgCl 2 C4H5N2OC4H5N2O

Empirical to molecular Since the empirical formula is the lowest ratio the actual molecule would weigh the same or more. This difference in weight would be by a whole number multiple. To find this multiple: divide the actual molar mass by the the mass of one mole of the empirical formula. You will get a whole number. Multiply the subscripts of the empirical formula by this number.

Example A compound has an empirical formula of ClCH 2 and a molar mass of 98.96 g/mol. What is its molecular formula? A compound has an empirical formula of CH 2 O and a molar mass of 180.0 g/mol. What is its molecular formula? Cl 2 C 2 H 4 C 6 H 12 O 6

Percent Composition to Molecular Formula: Ibuprofen is 75.69 % C, 8.80 % H, 15.51 % O, and has a molar mass of about 207 g/mol. What is its molecular formula? C 13 H 18 O 2

Example: Caffeine is 49.48% C, 5.15% H, 28.87% N and 16.49% O. It has a molar mass of 194 g. What is its molecular formula?  C  0.4948*194g = 95.99 g C  = 8 mol C  H  0.0515*194g = 9.99 g H  = 10 mol H  N  0.2887*194g = 56.01 g N  = 4 mol N  O  0.1649*194g = 31.99 g O  = 2 mol O C 8 H 10 N 4 O 2

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