# Mass Relationships in Chemical Reactions

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Mass Relationships in Chemical Reactions
Chapter 3 Mass Relationships in Chemical Reactions

Atomic Mass What is atomic mass?
Mass of an atom in atomic mass units (AMU) 1 AMU is the mass of 1/12 of a carbon-12 atom Also called atomic weight

Relative Atomic Mass What does the relative atomic mass of an element represent? Average mass of all known existing isotopes of that element It is “unitless” Proportioned based on abundance Ex. Carbon has a mass of which is an average of all of the carbon isotopes

Isotope Proportions A certain sample of element Z contains 60% of 69Z and 40% of 71Z. What is the relative atomic mass of element Z in this sample? 𝑥=60% %(71) 𝑥= (71) 𝑥= 𝑥=69.8

Isotope Proportions Chlorine exists as two isotopes, 35Cl and 37Cl. The relative atomic mass of chlorine is Calculate the percentage abundance of each isotope.

Molar Mass and NA What unit is used to measure the number of atoms/molecules? Moles (mol) – the number of atoms in 12 grams of a carbon-12 sample 1 mole = 6.02 x 1023 Avogadro's number (NA) We use it like we would a pair (2), dozen (12), or a gross (144) to simplify our math because it is freaking huge

How Big Is A Mole? If you would distribute 1 mole of pennies among the current population of the Earth, how much would everyone get? How long would it take to spend this amount if you would spend \$1,000/day? How many people could you make from 1 mole of cells? How long is 1 mole of seconds? If we took a mole of regular 8.5 x 11 inch sheets of paper and started laying them out side by side on the planet’s surface. What percentage of the Earth would be covered?

How Big Is A Mole? Answers
\$900 million dollars 2,500,000 years 10 billion 950,000 x age of the universe (14 billion yrs) 100 % …and it would be 17 million sheets thick

Molar Mass How is molar mass different from relative atomic mass?
It is the mass of one mole of a substance Abbreviated MM Same number as atomic mass, but with different units Units: 𝑔 𝑚𝑜𝑙 IB Units: g mol-1

Molar Mass What is the molar mass (MM) of the following elements?
Lithium Plutonium Bromine 6.94 𝑔 𝑚𝑜𝑙 𝑔 𝑚𝑜𝑙 𝑔 𝑚𝑜𝑙

Molar Mass How do we determine the molar mass of a molecule?
What is the molar mass of water? Add up the molar masses of each element within the molecule H2O MM = 2(H) + 1(O) MM = 2(1.01) + 1(16.00 ) MM = 𝑔 𝑚𝑜𝑙

Molecular Vs. Molar What is the difference between atomic, molecular and molar mass? Different units for different purposes Atomic/Molecular Mass  AMU’s Molar Mass  𝑔 𝑚𝑜𝑙 Can be used interchangeably

Molar Mass What is the molar mass of each of the following species:
KBr FeCl3 Sodium Hydroxide Lead (II) Oxide 𝑔 𝑚𝑜𝑙 𝑔 𝑚𝑜𝑙 𝑔 𝑚𝑜𝑙 𝑔 𝑚𝑜𝑙

Navigating How can we navigate between mass (m), moles (n) and the number of atoms, molecules or particles? We use molar mass (MM) and Avogadro's number (NA)

Double Circles

Double Triangles m N NA n n MM mass number moles moles molar mass
Avogadro's number n moles n moles MM molar mass

Mass-Mole Conversions
How many moles in 28 grams of CO2 ? What is the mass of 5 moles of Fe2O3 ? Find the number of moles of argon in 452 g of argon. Find the grams in 1.26 x 10-4 mol of HC2H3O2. Find the mass in 2.6 mol of lithium bromide. 1 – 0.64 mol 2 – 800 g 3 – 11.3 mol 4 – g 5 – 230 g

Mole-Number Conversions
How many moles of magnesium is 3.01 x 1022 atoms of magnesium? How many molecules are there in 4.00 moles of glucose, C6H12O6? How many moles are 1.20 x 1025 atoms of phosphorous? How many atoms are in moles of zinc? How many oxygen atoms are in moles of N2O5? 1 – mol 2 – 2.41E24 molecules 3 – 19.9 mol 4 – 4.52E23 atoms 5 – 1.21E14 oxygen atoms

To the right, To the right
How many atoms are in 20.0 grams of gold? Mass  20.0 g Divide by molar mass to get to moles 0.102 moles Multiply by Avogadro's number to get to atoms 6.14E22 Au atoms

To the left, To the left Number  1.00E24 atoms
What is the mass of 1.00E24 carbon atoms? Number  1.00E24 atoms Divide by Avogadro's number to get to moles 1.66 moles Multiply by molar mass to get mass 19.9 grams

Combined Find the mass in grams of 2.00 x 1022 molecules of diatomic fluorine. Find the number of molecules in 60.0 g of dinitrogen monoxide. How many molecules are in 5 mg of aspartame, C14H18N2O5? 1 – 1.26 g

Combined Calculate the mass, in grams, of 6.69x1021 ethane (C2H6) molecules. Urea [(NH2)2CO] is used for fertilizer and many other things. Calculate the number of N,C,O and H atoms in 1.68 x 104 grams of urea. The density of water is 𝑔 𝑚𝐿 at 4°C. How many water molecules are present in 2.56 mL of water at this temperature? 4 – 0.334g 5 – 3.37E26 N atoms, 1.69E26 C atoms, 1.69E26 O atoms, 6.74E26 H atoms 6 – 8.56E22 molecules

PRELAB 1 Gum

PRELAB 1 Sugar in Chewing Gum
How can we test for the mass of sugar in chewing gum?

PRELAB 1 Sugar in Chewing Gum
In your notebook, please calculate the following with proper uncertainties, sig figs and units. Experimental mass of sugar in the gum with the correct uncertainties Percent mass of sugar in your piece of gum Percent error = 𝐸𝑥𝑝 − 𝑇𝑟𝑢𝑒 𝑇𝑟𝑢𝑒 ×100

PRELAB 1 Sugar in Chewing Gum
Compare and contrast your measured percentage of sugar, and the actual percentage from the nutrition label for the brand of gum that you used. What are some possible reasons for any differences in these values, and how you might increase the accuracy of your data collection?

PRELAB 1 Sugar in Chewing Gum
What mathematical relationship/formula did you use to determine percent by mass? Why? If you were given one molecule of sucrose, C6H12O6, what information do you think you would need to figure out the percent mass of carbon? Why?

Percent Composition What is percent composition?
What two pieces of info do we need? Relative measure of the mass of each different element present in the compound 𝑃𝑎𝑟𝑡 𝑊ℎ𝑜𝑙𝑒 x 100 Mass of the element and the compound

Percent Composition How do we calculate it?
Calculate the mass of the compound Calculate the mass of each element 𝑚 𝑒𝑙𝑒𝑚𝑒𝑛𝑡 𝑚 𝑐𝑜𝑚𝑝𝑜𝑢𝑛𝑑 × 100

Percent Composition What is the percent mass of hydrogen in water?
2 hydrogens 2(1.01) = 2.02 g/mol Water is H2O 18.02 g/mol 2.02/18.02 x100 = 11.2% (tenths place)

Percent Composition Calculate the percent composition of oxygen in sodium sulfate. Na2SO4  g/mol 4 oxygens 4(16.00) = g/mol (64.00/142.04) x 100 = 45.1%

Percent Composition Tartrazine, or yellow dye # 5, is commonly found in many foods. Its molecular formula is C16H9N4Na3O9S2 . What is the percent composition of Carbon and Sulfur? The molar mass of Tartrazine is g/mol.

Working in Reverse If we start with %’s, what can that possibly lead us to? Working the formula in reverse and using mole ratios, we can get the empirical and possibly the molecular formula

Determination of the Empirical Formula
How do we determine it? Assume that you have 100% of the element and set equal to mass Divide each element by its molar mass Divide each by the smallest amount of moles If numbers aren’t close to whole, multiply all of them by a coefficient

Butane’s Empirical Formula
Butane is made up of only carbon and hydrogen. If hydrogen makes up 17.34% of butane’s mass and carbon the remaining 82.66%, what is the empirical formula of butane? C2H5 What is the molecular formula for butane if its molecular mass is g/mol? Multiply each subscript by 2 C4H10

Determine the Empirical Formula
Determine the empirical formula of a compound having the following percent composition by mass… K: 24.75% Mn: 34.77% O: % Empirical Formula: KMnO4 What is the molecular formula if its molecular mass is g/mol? ANSWER: KMnO4 (potassium permanganate)

Chemical Reactions and Equations
What is the difference between a chemical reaction and equation? A chemical reaction is the process of making a new substance(s) Ex. Iron oxidizing A chemical equation is a symbolic representation of the reaction 4Fe + 3O2 → 2Fe2O3

Chemical Reactions and Equations
How do we read a chemical equation? 4Fe(s) + 3O2(g) → 2Fe2O3(s) Reactants (left) Products (right) → Goes in one direction ↔ Reversible reaction Coefficients represent the mole ratios Notations (s, l, g, aq) represent phases/states Conservation of mass Balanced

Chemical Reactions and Equations
What is a balanced equation? The number of atoms on the left has to equal the number on the right Use coefficients to balance them Unbalanced: CH4 + O2 → CO2 + H2O Balanced:

Chemical Reactions and Equations
How do we balance the equations? KClO3 → KCl + O2 2KClO3 → 2KCl + 3O2 Al + O2 → Al2O3 4Al + 3O2 → 2Al2O3 C2H6 + O2 → CO2 + H2O 2C2H6 + 7O2 → 4CO2 + 6H2O 223 432 2746

Chemical Reactions and Equations
Balance the following chemical equations: K2CO3 + HCl  KCl + H2O + CO2 K2CO3 + 2HCl  2KCl + H2O + CO2 CaCO3 + HNO3  Ca(NO3)2 + H2O + CO2 CaCO3 + 2HNO3  Ca(NO3)2 + H2O + CO2 Pb(NO3)2 + NaI  PbI2 + NaNO3 Pb(NO3)2 + 2NaI  PbI2 + 2NaNO3 Al2(SO4)3 + NaOH  Al(OH)3 + Na2SO4 Al2(SO4)3 + 6NaOH  2Al(OH)3 + 3Na2SO4 12211 12111 1212 1623

Amounts of Reactants and Products
What is stoichiometry? The study of any numerical observation within a chemical reaction Using the mole method to determine how much reactant is needed (or product created) based on the number of moles

Amounts of Reactants and Products
What can be said about the reaction: H2 + O2 → H2O Reactants: Hydrogen and Oxygen Products: Water Unbalanced Balanced: 2H2 + O2→2H2O Proportion: 2 moles of hydrogen and 1 mole of oxygen create 2 moles of water

Amounts of Reactants and Products
How many moles of water should be formed with 8 moles of oxygen? What happens when our measurements are not in moles? 1:2 Ratio 8 moles of oxygen is equivalent to 16 moles of water Convert them into moles before starting using molar mass

Amounts of Reactants and Products

Amounts of Reactants and Products
I have the formula: Mg + HCl → MgCl2 + H2 What is the mass of MgCl2 that is formed when 20.0 g of HCl reacts with Mg? Balance it Mg + 2HCl → MgCl2 + H2 Convert into moles (20.0 g)/(36.45 g/mol) = mol HCl Use the mole ratio method 2:1 ratio → mol MgCl2 Convert back into mass 0.275 mol MgCl2 → 26.2 g

Amounts of Reactants and Products
What mass of silver nitrate as a solution in water would need to be added to 5.0 g of sodium chloride to ensure a complete precipitation of the chloride? AgNO3(aq)+ NaCl (aq)  AgCl(s) + NaNO3(aq) 15 g

Amounts of Reactants and Products
What mass of barium sulfate would be produced from 10.0 g of barium chloride in the following reaction? BaCl2 + H2SO4  BaSO4 + HCl Balanced: BaCl2 + H2SO4  BaSO4 + 2HCl 11.2 g

Amounts of Reactants and Products
What volume of ammonia gas would be needed to produce 40. g of ammonium nitrate in the following reaction. NH3 (g) + HNO3 (aq)  NH4NO3 (aq)

Amounts of Reactants and Products
In a fermentation reaction, glucose is converted to alcohol and carbon dioxide according to the following equation. What mass of alcohol and carbon dioxide would be produced from 10. g of glucose? C6H12O6  C2H5OH + CO2 Balanced: C6H12O6  2C2H5OH + 2CO2

Reaction Yield What is the difference between theoretical and actual yield? What is its purpose? Theoretical is the predicted amount of product via stoichiometry Actual is how much product you obtained experimentally To determine the efficiency of the procedure and/or experiment

Reaction Yield What is the % yield of CO2 if you started with g of O2 obtained g of CO2? CO + O2  CO2 Balanced: 2CO + O2 → 2CO2

Limiting Reagent What is a limiting reagent?
The reactant that is depleted first during a reaction is limiting Prevents a reaction from achieving 100% yield Any reactants remaining after the reaction completes are called excess reagents i.e. anything in excess cannot be a limiting reagent

Limiting Reagent 124 g of aluminum react with 601 g of iron (III) oxide. Calculate the mass of Al2O3 formed. Al + Fe2O3 → Al2O3 + Fe 2Al + Fe2O3 → Al2O3 + 2Fe Balance! Determine the number of moles of each reactant. Divide by the molar coefficient to determine the limiting reagent Use that number of moles to determine the amount produced using proper stoichiometry

Limiting Reagent Table
Reaction 2Al Fe2O3 Al2O3 2Fe Molar Mass (g/mol) Initial Mass (g) Initial Moles (mol) Limiting Reagent (mol) Final Moles (mol) Final Mass (g)

Limiting Reagent Table
Reaction 2Al Fe2O3 Al2O3 2Fe Molar Mass (g/mol) 26.98 159.70 101.96 55.85 Initial Mass (g) 124 601 Initial Moles (mol) Limiting Reagent (mol) Final Moles (mol) Final Mass (g)

Limiting Reagent Table
Reaction 2Al Fe2O3 Al2O3 2Fe Molar Mass (g/mol) 26.98 159.70 101.96 55.85 Initial Mass (g) 124 601 Initial Moles (mol) 4.60 3.76 Limiting Reagent (mol) Final Moles (mol) Final Mass (g)

Limiting Reagent Table
Reaction 2Al Fe2O3 Al2O3 2Fe Molar Mass (g/mol) 26.98 159.70 101.96 55.85 Initial Mass (g) 124 601 Initial Moles (mol) 4.60 3.76 Limiting Reagent (mol) 2.30 Final Moles (mol) Final Mass (g)

Limiting Reagent Table
Reaction 2Al Fe2O3 Al2O3 2Fe Molar Mass (g/mol) 26.98 159.70 101.96 55.85 Initial Mass (g) 124 601 Initial Moles (mol) 4.60 3.76 Limiting Reagent (mol) 2.30 Final Moles (mol) Final Mass (g) 367 235 257 Note: The mass of reactants equals the approximate mass of the products

Limiting Reagent How much chlorine is produced in the following reaction when g of manganese (IV) oxide reacts with 48.2 g of hydrochloric acid? MnO2 + 4HCl → MnCl2 + Cl2 + 2H2O Reaction MnO2 4HCl MnCl2 Cl2 2H2O Molar Mass (g/mol) Initial Mass (g) Initial Moles (mol) Limiting Reagent (mol) Final Moles (mol) Final Mass (g)

Limiting Reagent How much chlorine is produced in the following reaction when g of manganese (IV) oxide reacts with 48.2 g of hydrochloric acid? MnO2 + 4HCl → MnCl2 + Cl2 + 2H2O Reaction MnO2 4HCl MnCl2 Cl2 2H2O Molar Mass (g/mol) 86.93 36.46 125.83 70.90 18.02 Initial Mass (g) 47.25 48.2 Initial Moles (mol) Limiting Reagent (mol) Final Moles (mol) Final Mass (g)

Limiting Reagent How much chlorine is produced in the following reaction when g of manganese (IV) oxide reacts with 48.2 g of hydrochloric acid? MnO2 + 4HCl → MnCl2 + Cl2 + 2H2O Reaction MnO2 4HCl MnCl2 Cl2 2H2O Molar Mass (g/mol) 86.93 36.46 125.83 70.90 18.02 Initial Mass (g) 47.25 48.2 Initial Moles (mol) 0.5435 1.32 Limiting Reagent (mol) Final Moles (mol) Final Mass (g)

Limiting Reagent How much chlorine is produced in the following reaction when g of manganese (IV) oxide reacts with 48.2 g of hydrochloric acid? MnO2 + 4HCl → MnCl2 + Cl2 + 2H2O Reaction MnO2 4HCl MnCl2 Cl2 2H2O Molar Mass (g/mol) 86.93 36.46 125.83 70.90 18.02 Initial Mass (g) 47.25 48.2 Initial Moles (mol) 0.5435 1.32 Limiting Reagent (mol) 0.330 Final Moles (mol) Final Mass (g)

Limiting Reagent How much chlorine is produced in the following reaction when g of manganese (IV) oxide reacts with 48.2 g of hydrochloric acid? MnO2 + 4HCl → MnCl2 + Cl2 + 2H2O Reaction MnO2 4HCl MnCl2 Cl2 2H2O Molar Mass (g/mol) 86.93 36.46 125.83 70.90 18.02 Initial Mass (g) 47.25 48.2 Initial Moles (mol) 0.5435 1.32 Limiting Reagent (mol) 0.330 Final Moles (mol) 0.660 Final Mass (g)

Limiting Reagent How much chlorine is produced in the following reaction when g of manganese (IV) oxide reacts with 48.2 g of hydrochloric acid? MnO2 + 4HCl → MnCl2 + Cl2 + 2H2O Reaction MnO2 4HCl MnCl2 Cl2 2H2O Molar Mass (g/mol) 86.93 36.46 125.83 70.90 18.02 Initial Mass (g) 47.25 48.2 Initial Moles (mol) 0.5435 1.32 Limiting Reagent (mol) 0.330 Final Moles (mol) 0.660 Final Mass (g) 28.7 48.1 41.5 23.4 11.9

Excess Reagent If you started with g, how much manganese (IV) oxide is left in excess after the reaction is completed? 47.25 – 28.7 = 18.6 g of MgO2 excess Reaction MnO2 4HCl MnCl2 Cl2 2H2O Molar Mass (g/mol) 86.93 36.46 125.83 70.90 18.02 Initial Mass (g) 47.25 48.2 Initial Moles (mol) 0.5435 1.32 Limiting Reagent (mol) 0.330 Final Moles (mol) 0.660 Final Mass (g) 28.7 48.1 41.5 23.4 11.9

Limiting Reagent 0.709 g LR – ozone mol excess

Limiting Reagent Practice Problem – pg. 93 NH3 1124 g 319 g

Limiting Reagent Practice Problem – pg. 95 8.93 x 10^6 89%

Limiting Reagent Practice Problem – pg. 96 863 g 93%

Reaction Yield 7.05 g 93%