23 carbon atoms The number is known as Avogadro s d Number.

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2 THE MOLE (a counting unit).again! i A mole represents a set or group, much in the same way that a dozen represents a set of twelve. 1 dozen eggs = 12 eggs; 1 mol eggs = eggs 1 dozen carbon atoms = 12 carbon atoms; 1 mol carbon atoms = carbon atoms The number is known as Avogadro s d Number.

3 THE MOLE (a counting unit).again! i The number is known as Avogadro s Number. If you write out Avogadro s number, it looks like this: 602,200,000,000,000,000,000,000

4 THE MOLE (a counting unit).again! i Remember: 1 mole of atoms = atoms 1 mole of molecules = molecules 1 mole of formula units = formula units 1 mole of ions = ions

5 Atomic Mass vs. Molar Mass: Atomic mass = the mass of ONE ATOM expressed in atomic mass units (amu) Ex: Oxygen s atomic mass = amu; this is the average mass of 1 oxygen atom Molar mass = the mass of ONE MOLE of atoms, molecules, or formula units expressed in grams Ex: Oxygen s molar mass = g; this is the mass of 6.02X10 23 oxygen atoms

6 THE MOLE (a counting unit).again! i Atomic Mass vs. Molar Mass Element & Symbol Atomic Mass Average mass of 1 Atom Molar Mass Mass of 1 mole of atoms (6.02X10 23 atoms) Carbon (C) 12.0 amu 12.0 g C Helium (He) 4.00 amu 4.00 g He

7 ACIDS: You need to know these! Hydrochloric Acid= HCl Nitric i Acid = HNO 3 Sulfuric Acid = H 2SO 4 Carbonic Acid = H 2 CO 3 Phosphoric Acid=H 3 PO 4 Acetic Acid= CH 3 COOH

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9 I. CALCULATING MOLAR MASS: 1. Phosphoric acid

10 I. CALCULATING MOLAR MASS: 2. Calcium Nitrate

11 I. CALCULATING MOLAR MASS: 3. Iron (III) Carbonate

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13 II. FINDING PERCENT COMPOSITION: Percent Composition = is the percent by mass of each element in the compound. The percent composition is always the same regardless of the size of the sample. Ex: H 2 0 is ALWAYS 11.2 % hydrogen and 88.8% 8% oxygen (by mass)

14 II. FINDING PERCENT COMPOSITION: The percent composition of the elements The percent composition of the elements in a compound adds up to 100%.

15 II. FINDING PERCENT COMPOSITION: Formula Used: Molar Mass of the element in a compound Total Molar Mass of the compound X 100 Or think of it as: Part Whole X 100

16 II. FINDING PERCENT COMPOSITION: Steps: 1. Find molar mass of each element (parts) 2. Find the total molar mass of the compound (whole) 3. Part Whole X Evaluate your answer (percentages should add to approximately 100%)

17 II. FINDING PERCENT COMPOSITION: Ex: Find the percent composition of aluminum sulfate.

18 II. FINDING PERCENT COMPOSITION: NOTE: Therefore, a 100g sample of Al 2 (SO4) 3 would contain g 16 Al, g S, and g O

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20 III. CONVERSIONS BETWEEN GRAMS & MOLES KEY IDEA: It is important to know the following conversion: The molar mass of a compound or the mass an element is equal to 1 mole of that compound or element. Ex: 1 mole of carbon is equal to 12 grams of carbon! Ex: 1 mole of water is equal to 18 grams (molar mass) of water

21 III. CONVERSIONS BETWEEN GRAMS & MOLES Use a T-chart to convert from what you know to what you do not know. Use your conversion factors so units cancel out!

22 III. CONVERSIONS BETWEEN GRAMS & MOLES Ex #1: How many moles are represented by 11.5 g of magnesium hydroxide

23 III. CONVERSIONS BETWEEN GRAMS & MOLES Ex #2: How many grams of aluminum sulfide are Ex #2: How many grams of aluminum sulfide are present in 0.44 moles of aluminum sulfide?

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25 IV. CALCULATION of FORMULAS: 2 types of formulas: 1. Molecular formula (M.F.) = shows the types and numbers of atoms combined in a single molecule. Ex: C 6 H 12 O 6 (glucose) Actually has 24 atoms!

26 IV. CALCULATION of FORMULAS: 2. Empirical formula (E.F.) = a chemical formula showing the simplest whole number ratio of atoms in a compound. Ex: Reduce glucose C 6 H 12 O 6 by dividing g y g all the subscripts by 6 the empirical formula would be CH 2 O 2

27 IV. CALCULATION of FORMULAS: In the chart below, fill in the empirical formula given the molecular formula: Molecular Formula H 2 O 2 H 2 O Empirical Formula HO H 2 O 2 C 8 H 16 CH 2 C 2 H 4 CH 2

28 IV. CALCULATION of FORMULAS: Notice 2 things: 1. Some molecular formulas can t be reduced (H 2 O) 2. Several compounds can share the same E.F., but each compound has its own unique molecular formula Molecular Formula H 2 O 2 H 2 O Empirical Formula HO H 2 O 2 2 C 8 H 16 CH 2 C 2 H 4 CH 2

29 IV. CALCULATION of FORMULAS: WHY DO WE USE THE EMPIRICAL FORMULA IF IT CONTAINS LESS INFORMATION? It is easier to experimentally determine the empirical formula of a compound than the molecular formula. So the E.F. is usually found 1 st as a step towards finding the molecular formula.

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31 IV. CALCULATION of FORMULAS: Steps to finding an EMPIRICAL FORMULA: 1. The amount of each element should be listed in grams. If analysis of the compound is in percent, convert to grams: assume a 100 g sample of the compound. 2. Convert grams of EACH element to moles (T-chart). 3. Divide moles of each element by the smallest number of moles. 4. Round each answer from 3 to the nearest whole number and write the empirical formula using these numbers as subscripts.

32 EMPIRICAL FORMULAS: Ex #1: What is the empirical formula for a compound if a sample contains 0.9g of calcium and 1.6g of chlorine?

33 EMPIRICAL FORMULAS: Ex # 2: What is the empirical formula for a compound that is 40% C, 6.71% H, and 53.3% O?

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35 Steps to finding a MOLECULAR FORMULA: 1. If it is not given, determine the empirical formula of the compound. (Follow all steps necessary to determine an empirical formula) 2. Calculate molar mass of the empirical formula. 3.Divide the molar mass of the compound by the molar mass determined from the empirical formula. 4 Round the answer to 3 to the nearest whole 4.Round the answer to 3 to the nearest whole number and multiply all subscripts in the empirical formula by this number.

36 MOLECULAR FORMULAS: Ex #1: What is the molecular formula of a substance that has an empirical formula of AgCO 2 and a molar mass of 304g/mol?

37 MOLECULAR FORMULAS: Ex #2: An unknown compound contains 85.64% carbon and 14.36% hydrogen. It has a molar mass of g/mol. Find its molecular formula.

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39 V. HYDRATES: Suppose an ionic substance is dissolved in water. The water can be evaporated to leave the solid ionic compound. SOME ionic compounds, however, will form solid crystals that incorporate water molecules (where the water molecules are weakly attracted to the ions in the crystal structure).

40 V. HYDRATES: Hydrate = an ionic compound containing water molecules incorporated into its solid crystal structure In other words, a hydrate is a collection of anions (negative ions), cations (positive ions), and water molecules

41 V. HYDRATES: Anhydrous salt = the ionic compound that remains after the water has been removed (usually by heating) from the hydrate Note: salt = ionic compound (usually an ionic compound that does not contain OH ions)

42 V. HYDRATES: The heating of a hydrate to produce an anhydrous salt can be illustrated as follows: hydrate + heat anhydrous salt + water

43 V. HYDRATES: Prefixes are used as coefficients in the following manner in the chemical formulas for hydrates. The chemical formula for magnesium sulfate heptahydrate is MgSO 4 7 H 2 O 7 moles of H 2 O are associated with every 1 mole of MgSO 4.

44 V. HYDRATES: The chemical formula for barium hydroxide octahydrate is Ba(OH) 2 8 H 2 O 8 moles of H 2 O are associated with every 1 2 y mole of Ba(OH) 2.

45 V. HYDRATES: What is the name of the following hydrate, FePO 4 4H 2 O? Iron III phosphate tetrahydrate

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47 V V. HYDRATES: MOLAR MASS OF HYDRATES: When determining the molar mass of a hydrate, the molar mass of the associated water must be included.

48 V V. HYDRATES: MOLAR MASS OF HYDRATES: EX #1: Calculate the molar mass of calcium sulfate dihydrate.

49 V. HYDRATES: % Composition PERCENT COMPOSITION of HYDRATES: Steps: 1. Find molar mass of water. 2. Find the molar mass of the salt. 3. Add the mass of the water and the salt in order to get the total mass of the hydrate. Mass of Water (part) Mass of Hydrate (whole) X 100

50 V. HYDRATES: % Composition Ex: What percentage of water is found in sodium sulfide nonahydrate? hd t?

51 V. HYDRATES: Empirical Formula Steps: 1. Identify what you know and what you do not know. 2. All amounts should be listed in grams. If analysis is in percent, convert to grams: assume a 100 g sample. 3. Convert grams of anhydrous salt to moles. 4. Convert grams of water to moles. 5. Divide moles by the smallest number of moles. 6. Round each answer from 5 to the nearest whole number and these numbers become the COEFFICIENTS for the salt and water.

52 V. HYDRATES: Empirical i Formula Ex: Suppose a hydrate contains g barium iodide and 0.887g Ex: Suppose a hydrate contains g barium iodide and 0.887g water. Determine the formula of the hydrate.