Moles and Stoichiometry

The Mole OBJECTIVES: Describe the mole concept Calculate the mass of a mole of any substance. Convert between moles, grams, liters, and particle number

What is a Mole 摩尔? We measure mass in grams. g We measure volume in liters. L We count pieces in MOLES. mol

The Mole Concept A Carbon-12 atom has a mass of 12amu A mole of Carbon atoms has a mass of 12 grams C

Gram Atomic Mass Equals the mass of 1 mole of an element Written on the Periodic Table 12.01 grams of C has the same number of pieces as 1.008 grams of H and 55.85 grams of iron. We can write this as 12.01 g C = 1 mole C We can count things by weighing them.

The Mole Concept Atomic Mass in grams Mole of atoms A mole of aluminum = A mole of gold = A mole of silver = A mole of boron = 27.0g 197g 108g 10.8g

The Mole Concept So, How many atoms are in a mole? Does a mole of H have the same number of atoms as a mole of He?

If a Helium atom is 4 times heavier than a Hydrogen atom, then a dozen Helium atoms is 4 times heavier than a dozen Hydrogen atoms.

And a mole of Helium atoms is 4 times heavier than a mole of Hydrogen atoms.

The number of atoms in a mole is called, So, the number of atoms in a mole is always the same The number of atoms in a mole is called, Avogadro's Number Avogadro's Number = 6.022 x 1023

Mole – Particle Conversions The mole concept allows us to count atoms, molecules, formula units and ions. 1 mole of Al = 6.022 x 1023 atoms of Al So how many atoms in 3 mol of Al?

Mole – Particle Conversions 1 mole of Al = 6.022 x 1023 atoms of Al So how many atoms in 3 mol of Al? 3 mol Al 6.022 x 1023 atoms of Al 1 mol Al = 1.8066 x 1023 atoms of Al

Conversions 1 mole of Al = 6.022 x 1023 atoms of Al So how many moles are 3.0 x 1023 atoms of Al? 3.0 x 1023 atoms Al 1 mol Al 6.022 x 1023 atoms of Al = .5 mol of Al

How many moles of Na atoms are there in 46.0g of Na? Converting into Moles How many moles of Na atoms are there in 46.0g of Na? Na has a mass of 23.0 46.0g Na 23.0g Na 1 mol Na = 2 mol Na 23.0 Step 1: Write a grid and place the given number into the upper left hand part of the grid Step 3: Place the units you need to cancel on the bottom, and multiply by the top and divide by the bottom Step 2: Look up the atomic mass on the periodic table and find out how many grams = 1mole

Mole-Mass Conversations Dimensional Analysis- converting between physical properties using ratios How many grams are in 3.5 mol CO2? How many moles are in 150g in NaBr? 3.5 mol CO2 44.0 g CO2 =154g CO2 1 mol CO2 150 g NaBr 1 mol NaBr = 1.5 mol NaBr 102.9 g NaBr

28.1 g C 1 mol Mg 8.60 x 1022 atoms Li Examples How much would 2.34 moles of carbon weigh? How many moles of magnesium is 24.31 g of Mg? How many atoms of lithium is 1.00 g of Li? 28.1 g C 1 mol Mg 8.60 x 1022 atoms Li

What about compounds? In 1 mole of H2O molecules there are 2 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 they would weigh add them up

Types of Molar Mass Gram Molecular Mass (GMM)- the total number of atoms in a molecular compound Cl2 = 2 x 35.4 g = 70.8 g CH4= Gram Formula Mass (GFM)- the total number of atoms in an ionic compound NaCl = (1 x 23.0g) + (1 x 35.4g) = 58.4g Ca(OH)2= (1 x 12.0g) + (4 x 1.0g) = 16g (1 x 40.0g) + (2 x (16.0g+1.0g))= 74g

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 3) gram atomic mass

Examples = 78.1 g = 92.0 g = 164.1 g = 180.0 g = 149.0 g Na2S N2O4 Calculate the molar mass of the following and tell what type it is: Na2S N2O4 Ca(NO3)2 C6H12O6 (NH4)3PO4 = 78.1 g = 92.0 g = 164.1 g = 180.0 g = 149.0 g

0.104 mol CO2 178 g H2O 0.425 mol CH4 Examples How many moles is 4.56 g of CO2? How many grams is 9.87 moles of H2O? How many molecules is 6.8 g of CH4? 0.104 mol CO2 178 g H2O 0.425 mol CH4

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.

Standard Temperature and Pressure 0ºC and 1 atm pressure （1个大气压，约为101.325kPa） 0oC = 32oF= 273 K 1 atm= 101.3 kPa = 760 mmHg (torr) abbreviated STP 标准状况 At STP 1 mole of gas occupies 22.4 L Called the molar volume 摩尔体积 1 mole = 22.4 L of any gas at STP

Examples What is the volume of 4.59 mole of CO2 gas at STP? How many moles is 5.67 L of O2 at STP? 22.4 L CO2 4.59 mol CO2 =103 L CO2 1 mol CO2 5.67 L O2 1 mol O2 =0.253 mol O2 22.4 L O2

Ideal Gas Law Connection between the number of particles (n) and the pressure (P), volume (V), and temperature (T) of a gas PV=nRT R= 8.31 kPa∙L/ mol∙K T= ALWAYS in Kelvin, so convert oC to K -50oC + 273 = 223K How many moles of helium are contained in a 5.00-L canister at 101 kPa and 30oC? n= PV/RT n= 101kPa x 5.00-L 8.31 kPa∙L/mol∙K x 303K n= 0.2 mol

Stoichiometry化学计量法 It starts with a balanced equation 2H2 + O2 ® 2H2O “Stoichiometry” is Greek for “Measuring Elements” It starts with a balanced equation 2H2 + O2 ® 2H2O 2 moles of hydrogen reacts with 1 mole of oxygen Forming 2 moles of water.

Stoichiometry The coefficients tell us how many moles of each substance. Not Grams! For example: 2H2 + O2 ® 2H2O 2 g of H2 + 1 g of O2 = 2 g of H2O 3 g of reactants can’t make only 2 g of products

Mass of a Product 2H2 + O2 ® 2H2O 2 moles H2 2.02 g H2 = 4.04 g H2 The Law of Conservation of Mass applies Convert the moles to grams and the equation does work. 2H2 + O2 ® 2H2O 2 moles H2 2.02 g H2 = 4.04 g H2 1 mole H2 1 mole O2 32.00 g O2 = 32.00 g O2 1 mole O2 36.04 g H2+O2

Mass of a Product 2H2 + O2 ® 2H2O 2H2 + O2 ® 2H2O 18.02 g H2O 2 moles H2O 18.02 g H2O 36.04 g H2O = 1 mole H2O 2H2 + O2 ® 2H2O 36.04 g H2 + O2 = 36.04 g H2O

2Na + Cl2  2NaCl 2Na (s) + Cl2(g) 2NaCl (s) How many grams of sodium are needed to react with .071g of chlorine gas? 2Na (s) + Cl2(g) 2NaCl (s) Mole Ratio 2 1 2 Mass Ratio 23 x 2= 46 35.5 x 2 x 1= 71 58.5 x 2= 117 1 mol Cl2 2 mol Na 0.071 g Cl2 46 g Na 71 g Cl2 1 mol Cl2 2 mol Na = 0.046 g Na

Chemical Yield The amount of product made in a chemical reaction. There are three types: 1.Theoretical yield 理论产量 - the amount of Product that should be made (from calculations) 2. Actual yield 实际产量- the amount of Product formed in the laboratory (always given)

Chemical Yield 3. Percent yield – a percentage/ratio between the actual yield and the theoretical yield. % Yield = % yield tells us how “efficient” a reaction is. % yield can not be bigger than 100 %. Actual Yield x 100 Theoretical Yield

Example 11.8 g NaCl x 100 13.6 g NaCl Answer = 86.7 % According to your calculations the theoretical yield for the production of NaCl is 13.6 grams. In the laboratory your actual yield is 11.8 grams of NaCl. What is the percent yield? 11.8 g NaCl x 100 13.6 g NaCl Answer = 86.7 %

Calculating Percent Composition质量分数of a Compound Like all percent problems: Part whole Find the mass of each component, then divide by the total mass. x 100 %

Calculating Percent Composition质量分数of a Compound Find the mass percent for the elements in Sodium hydrogen carbonate: NaHCO3 -molar mass is 84 g/mol -mass of: Na= 23g H= 1g C= 12g O= 3 x 16= 48g %C = (12g/84g) x 100= 14.3% %Na = (23g/84g) x 100= 27.4% %H = (1g/84g) x 100= 1.2% %O = (48g/84g) x 100= 57.1%

The Empirical Formula 经验式 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. CH2 is an empirical formula C2H4 is a molecular formula C3H6 is a molecular formula H2O is both empirical & molecular

Calculating Empirical Just find the lowest whole number ratio C6H12O6 CH4N 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.

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 mole value

Example Calculate the empirical formula of a compound composed of 38.67 % C, 16.22 % H, and 45.11 %N. Assume 100 g so 38.67 g C x 1mol C = 3.220 mole C 12.01 g C 16.22 g H x 1mol H = 16.09 mole H 1.01 g H 45.11 g N x 1mol N = 3.219 mole N 14.01 g N

Example The ratio is 3.220 mol C = 1 mol C 3.219 mol N 1 mol N The ratio is 16.09 mol H = 5 mol H 3.219 mol N 1 mol N = C1H5N1 = CH5N Caffeine is 49.48% C, 5.15% H, 28.87% N and 16.49% O. What is its empirical formula?

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? C4H5ON2 = 97.11g Ratio= 194g/ 97.11g = 2 2(C4H5ON2) = C8H10O2N4; molecular formula

Example A compound is known to be composed of 71.65 % Cl, 24.27% C and 4.07% H. Its molar mass is known (from gas density) to be 98.96 g. What is its molecular formula?

Final Exam What is matter? Compounds; elements; substances vs. mixtures (Homogeneous and Heterogeneous) Atomic symbols; Naming compounds Periodic table trends: Electronegativity, Atomic Radius, Ion Size, etc… Reaction energy; exothermic vs. endothermic; activation energy Solvents, solutes, and solutions Balancing Equations Valence electrons Structure of an Atom; Molecular structures Alpha, Beta, and Gamma Decay Group names: Halogens, transition metals, alkali metals, etc… Properties of metals, non-metals, metalloids, and semiconductors

Final Exam Lewis Dot Structures Types of reactions Orbitals and sub-orbitals Ionic vs. Covalent bonding Temperature and Kinetic motion Equilibrium and shifting the direction of reactions Calculate: Density Wavelength and Frequency Atomic Mass Half life Radioactive decay Moles; Mass percent, Percent yield, Mass-Mole conversions