CHEM 5013 Applied Chemical Principles Chapters Three and Four (Mole Concepts) Professor Bensley Alfred State College

Chapter Objectives Explain the concept of a mole in your own words. Interpret chemical equations in terms of both moles and molecules. Interconvert between mass, number of molecules, and number of moles. Determine a chemical formula from elemental analysis (i.e., from % compositions).

Chapter Objectives Define the concentration of a solution and calculate the molarity of solutions from appropriate data. Calculate the molarity of solutions prepared by dilution or calculate the quantities needed to carry out a dilution to prepare a solution of a specified concentration. Calculate the amount of product expected from a chemical reaction, given the amounts of reactants used.

Chapter Objectives Calculate the amounts of reactants needed in a chemical reaction to produce a specified amount of product. Identify a limiting reagent and calculate the amount of product formed from a nonstoichiometric mixture of reactants. Calculate the percentage yield of a chemical reaction.

Molecular Weight Remember atomic weight? Molecular Weight – Expressed in amu Example: H2O

Formula Weight Formula weight: Formula weight (FW) covers both ionic and molecular compounds NaCl: FW =

Examples Calculate the formula weight of the following compounds to 3 sig figs: Calcium hydroxide Methylamine CH3NH2

The Mole A mole is: A. B. C. D.

A chemical mass unit, defined to be 6.022 x 1023 molecules, atoms, or some other unit.

The Mole You have one car. How many engines do you have? How many wheels do you have? You have 1 dozen cars. How many dozens of engines do you have? How many dozens of wheels do you have? You have 1 mole of cars. (1 Chemist’s Dozen) How many moles of engines do you have? How many moles of wheels do you have? 12 x 6.02 x 1023 x

The Mole You have one molecule of CCl4. How many Carbon atoms do you have? How many Chlorine atoms do you have? You have 1 dozen molecules of CCl4. How many dozen Carbon atoms do you have? How many dozen Chlorine atoms do you have? You have 1 mole of CCl4. (Chemist’s Dozen) How many moles of Carbon atoms do you have? How many moles of Chlorine atoms do you have? 12 x 6.02 x 1023 X

The Mole Example: One mole of Na2CO3 contains how many moles of Sodium ions? How many actual sodium ions? How many moles of carbonate ions? How many actual carbonate ions? Think of it as (CO3)1

The Mole 1 Mole of Oxygen atoms (O) contains how many O atoms? But 1 mole of Oxygen molecules (O2) contains how many O atoms?

Molar Mass Molar mass: What is molar mass of carbon-12? How many grams in one mole? Molar mass in grams per mole is numerically equal to the formula weight in amu.

Examples How many molecules of HNO3 are present in 2.5 moles HNO3? What is the mass in grams of one nitric acid molecule, HNO3?

Mole Calculations Two VERY important mole calculations: How much does a given number of moles of a substance weigh? (convert moles to grams) Also, how many moles are in a given mass of a substance? (convert grams to moles)

Mole Calculations A sample of nitric acid contains 0.253 mol HNO3. How many grams is this? A mixture for an acid used on a construction project calls for 25 grams of Sulfuric Acid (H2SO4) to be used. How many moles of sulfuric acid is this?

Mole Calculations The formulation for a test batch of structural steel contains 0.05% Silicon by mass. This calculates out to 1.0x10-6 gram for your formulation. How many atoms of Silicon were added to the batch to produce the correct steel formulation?

Determining Chemical Formulas Percent composition of a compound = Mass percentage: # grams of A in 100 g of the whole thing mass of A in the whole Mass %A = 100 x mass of the whole

Example Lead(II) chromate, PbCrO4 is used as a paint pigment (yellow). What is the percentage composition of lead(II) chromate?

Example The chemical name of table sugar is sucrose, C12H22O11. How many grams of carbon (C) are there in 61.8 grams of sucrose?

Determining Chemical Formulas Empirical formula: Example: H2O2

Example Sodium pyrophosphate is used in detergent preparations. The mass percentages of the elements in this compound are 34.6% Na, 23.3% P, 42.1% O. What is the empirical formula of sodium pyrophosphate?

Molecular Formula from Empirical Formula Need 2 things to determine MF: Molecular weight = n x empirical formula weight So, n = molecular weight empirical formula weight

Example Hexamethylene is one of the materials used to produce a type of nylon. Elemental analysis of the substance gives 62.1% C, 13.8% H and 24.1% N. Its molecular weight is 116 amu. What is its molecular formula?

Stoichiometry Definition: Based on:

Stoichiometry N2 (g) + 3H2 (g)  2NH3 (g) H2 molecules to produce N2 molecules react with H2 molecules to produce NH3 molecules of N2 reacts with of H2 to produce of NH3

Stoichiometry N2 (g) + 3H2 (g)  2NH3 (g) Because moles can be converted to grams, can also say: How many grams of nitrogen will react with 6.0 grams of hydrogen?

balanced chemical equation!!! Stoichiometry The number of moles involved in a reaction is proportional to the coefficients in the balanced chemical equation!!!

Example How many moles of NH3 could we obtain from 3 moles of H2? How many moles of NH3 could we obtain from 4.8 mol H2?

Stoichiometry N2 (g) + 3H2 (g)  2NH3 (g) Can also calculate problems involving masses of reactants or products N2 (g) + 3H2 (g)  2NH3 (g) How much hydrogen (in kg) is needed to yield 907 kg of ammonia?

Flow Chart for ANY Stoichiometry Problem Grams of A X Conversion Factor: grams A to mol A Flow Chart for ANY Stoichiometry Problem X Conversion Factor: mol A to mol B X Conversion Factor: mol B to grams B Grams of B

Example How many grams of HCl are required to react with 5.00 grams of manganese dioxide according to the equation?

Limiting Reagent What happens when we don’t exactly follow the recipe? What happens when the L.R. is used up? So what determines the number of moles (amount) of product that we can obtain in a reaction?

Limiting Reagent 100 seats and 300 tires. How many bicycles can you make? 1 seat + 2 tires  1 bicycle The are the limiting reagent

Limiting Reagent If 0.30 mol Zn is added to hydrochloric acid containing 0.52 mol HCl, how many moles of H2 are produced?

Limiting Reagent Urea, CH4N2O, is used as a nitrogen fertilizer. It is manufactured from ammonia and carbon dioxide. 2NH3 + CO2  CH4N2O + H2O 10.0g NH3 and 10.0g CO2 are reacted together. What is the maximum quantity (in grams) of urea than can be obtained?

Theoretical Yield Theoretical yield: Percentage yield:

Working with Solutions Molar concentration or Molarity Moles of solute Liters of solution Molarity (M) =

Molarity 0.200 M (0.200 molar) solution of HCl is how many moles of HCl dissolved in 1 liter of water? How many grams of HCl dissolved in 1 liter of water? Example: You place a 1.53 gram sample of potassium dichromate, K2Cr2O7, into a 50.0 mL volumetric flask and add water to bring the solution up to the mark on the neck of the flask. What is the molarity of the solution?

Example A solution of sulfuric acid (H2SO4) has a concentration of 0.154 M. How many moles of sulfuric acid are contained in a 500 mL bottle of the solution? How many grams of sulfuric acid are in the 500 mL solution?

Diluting Solutions You have a 10 M solution of HCl. Suppose however, you want a 1 M solution. How do we make this 1 M solution of HCl? Dilution formula derivation

Diluting Solutions A stock solution of concentrated hydrochloric acid is 12.1M. How much of this stock solution is needed to prepare 1.00 L of an aqueous solution, which is 0.25M HCl?