2Mole DefinedMole = number equal to the # of carbon atoms in exactly 12 grams of pure C-12.Mole = x 1023Called Avogadro’s numberOne mole of protons = 1gOne mole of neutrons = 1gOne mole of an element = atomic mass in grams
3Molar Mass and related terms Molar mass – mass in grams of one mole of a substance– molecular weight, mass of 1 molecule in amuFormula weight, mass of 1 formula unit for an ionic compound in amuCalculate by summing the masses of the component atoms, units:molar mass – grams or grams/molemolecular wt & formula wt - amu
4Moles, mass and # particles Molar mass links the mass of a substance to the number of particles present1 mole Mg = 24.31g = x 1023 Mg atoms
5Molar Mass Related Calculations: Molar mass of a substance.Moles present in a given mass of substance.Mass of a given number of moles of a substance.Number of particles in a given mass or a given number of moles of a substance.
6What is the molar mass of glucose. The formula for glucose is C6H12O6. What is the mass of moles of glucose?
7How many glucose molecules are present in 0.023 moles of the compound? How many moles of glucose are present in 3.5 x 10-3 grams of the substance?
8Mass PercentCompounds are typically described by either their chemical formula or their percent by mass of the component elements.Mass % X = n (molar mass X) x 100%molar mass of compound
9Mass Percent Calculations Calculate the mass percent of each element in C6H12O6Assume one mole of the substance.
10Empirical and Molecular Formulas Molecular formula – ratio of atoms in a moleculeEmpirical formula – simplest ratio of elements in a moleculeGlucose:Molecular formula: C6H12O6Empirical Formula:Molecular formula = n (empirical formula)
11Mass % Empirical Formula Given mass percent data:“Calculate” mass in grams of each element in 100 g of compound.Convert each mass into moles of the element.Divide each molar answer by the smallest of the values.If the numbers obtained in step 3 are not whole numbers, multiply all by an integer so the results are whole numbersWhole numbers obtained in step ¾ are the subscripts in the empirical formula.
12Empirical Formula Molecular Formula Molar mass neededCalculate mass of one mole of the empirical formula.Molar Mass = integer (n)empirical formula weight(n)(empirical formula) = molecular formula
13Caffeine Molar mass = 194 g/mol 49.49 % C 5.19 % H 28.85 % N 16.48 % O What is the empirical and molecular formula of caffeine?
14Acetaminophen (Tylenol) Molar mass = 151 g/mol63.56 % C6.00 % H9.27 % N21.17 % OWhat is the empirical and molecular formula of acetaminophen?
15CH 3: #86Urea: Molar Mass 60 g/mol (I looked this up – not in question)1.121 g N0.161 g H0.480 g C0.640 g OWhat is the empirical and molecular formula of urea?
163.7/3.8 Chemical Reactions Writing chemical reactions Write the correct chemical formula for each reactant and product.Use a subscript after each formula to indicate the state of each substance(s) – solid(l) – liquid(g) – gas(aq) – aqueous (dissolved in water)
17Chemical equations must obey the law of conservation of matter – balancing does this. Balance the equation by adding coefficients in front of reactants and products as neededDO NOT CHANGE THE FORMULAS FOR THE COMPOUNDS
18One of my favorite chemical reactions: Mg(s) HCl(aq) MgCl2 (aq) + H2 (g)As written the reaction does not obey the law of conservation of matter – reaction needs to be balanced
19Mg(s) + 2 HCl(aq) MgCl2 (aq) + H2 (g) Now the reaction is balanced!
23Cookie example! 2 eggs + 1 bag chips 50 cookies How many cookies could you make if you had only one egg?How many cookies could you make if you had 2 bags of chips?
24Molar RatiosBalanced reactions lead to molar ratiosN H 2 NH3
25N2 (g) H2 (g) NH3 (g)If 3.5 grams of N2 to react, how many moles and how many grams of NH3 would be made?
26N2 (g) H2 (g) NH3 (g)How many grams of H2 are needed to make 37.8 grams of NH3?
272 LiOH + CO2 Li2CO3 + H2OHow many grams of LiOH are needed to react 750. grams of CO2?How many grams of Li2CO3 will be made if 750. grams of CO2 react?
28Limiting ReagentReactants are not always combined in stoichiometric quantities.Often one reactant is used up before others.This reactant is said to be the limiting reagent (or reactant.)this reactant limits how much product can be made.
29Limiting Reagent Calculations When you are given masses for each reactant you must determine which reactant is limiting.Convert grams of each reactant to moles.Use the molar ratios to determine which reactant is limiting.Base the amount of product that can be made on the limiting reagent.
30Another Approach… Convert grams of each reactant to moles. Calculate the moles (or grams) of a product that could be made from each reactant.Whichever reactant results in the smaller quantity of product is the limiting reagent.Base the amount of product made on the limiting reagent.
31N2 (g) H2 (g) 2 NH3 (g)12.5 grams of nitrogen is combined with 2.30 grams of hydrogen.Which reactant is in excess and which is limiting?How many grams of ammonia will be made?
32Percent Yield% Yield = actual yield x 100 %theoretical yield