Unit B – Analytical Stoichiometry Lundquist -- 2015

Unit B.1 Gravimetric analysis

Mass Spectrometer

Lots of Arguing <1850 the mass of atoms was based on Hydrogen H = 1 atomic mass unit 1850-1956 used Oxygen O = 16 amu Making H 1 16 of O Small problem (1919) isotopes (O with a mass of 17 & 18) Made 2 different systems (O and 1 16 O) 1961 based off 6 12 𝐶 Was already a base in physics for masses More stable isotope 1 amu = 1 12 mass of 1 6 12 𝐶 nucleus

6 12 𝐶 6 13 𝐶 Carbon-13 Carbon-12 Carbon with a mass of 13 6 protons 7 neutrons Carbon-12 Carbon with a mass of 12 6 protons 6 neutrons

Average Atomic Mass Number of protons (+) charge in the nucleus Number of e- if neutral Average atomic mass Isotopes (heavier/lighter atoms) Weighted average

Average Atomic Mass 𝐴𝑣𝑒𝑟𝑎𝑔𝑒.𝐴𝑡𝑜𝑚𝑖𝑐.𝑀𝑎𝑠𝑠=( 𝑚 1 % 1 )+( 𝑚 2 % 2 )+( 𝑚 3 % 3 )... Mass of isotope Percent abundance as a decimal

ADVANCED PROBLEM A sample of argon contains 2 isotopes 39 𝐴𝑟 and 40 𝐴𝑟 , given the average atomic mass of argon what is the percent abundance of each isotope?

B.1 Note Quiz Questions 1.

The mole Number of carbon atoms in exactly 12.0 g of 12 𝐶 6.022 x 1023

Molar Mass (Formula Weight) The mass of 6.022 x 1023 ___________ of a substance Atoms if an element (Au, C, Hg) Molecules compounds (C6H12O6, CO2, H2O) Polyatomic elementals (O2, S8, P4) Formula units if a salt (CaO2, NaCl, MgSO4)

B.1 Note Quiz Questions 2. 3. 4. 5.

Percent Composition Percent by Mass Mass percent What part of a substance’s matter is a particular element Molar mass including subscripts

Percent by Mass What is the percent by mass of each element in ethanol (C2H5OH)

B.1 Note Quiz Questions 6. 7. a. b. c. d.

When in doubt, burn it.

Formulas Empirical Formula Molecular Formula Simplest ratio of each element For ionic compounds (salts) there is only empirical formulas Actual number of each element present For molecular compounds (all non-metals)

B.1 Note Quiz Questions 8. a. b. c. d.

The Poem By Mrs. Freeman Percent to mass Mass to mole Divide by small Multiple till whole

Example A white powder is analyzed and found to contain 43.64% P and 56.36% O by mass. The compound has a molar mass of 283.88 g/mol. What are the compound’s empirical and molecular formulas?

B.1 Note Quiz Questions 9. 10.

Problem A compound is composed of carbon, nitrogen, and hydrogen. When 0.1156 g of this compound is reacted with oxygen, 0.1638 g of carbon dioxide, and 0.1676 g of water are collected. Determine the empirical formula of the compound.

Problem (continued) A compound is composed of carbon, nitrogen, and hydrogen. When 0.1156 g of this compound is reacted with oxygen, 0.1638 g of carbon dioxide, and 0.1676 g of water are collected. Determine the empirical formula of the compound. If the molar mass of the is 31 𝑔 𝑚𝑜𝑙 what is the molecular formula?

Hydrates Also known as dot waters CoCl2 & CoCl2.6H2O Water molecules can fit between the ions of a salt Anhydrous – no water Hydrate – water is present Can pull out the water with heat

Hydrates A calcium chloride hydrate has a mass of 4.72 g, after heating for several minutes the mass of the anhydrate is found to be 3.56 g. Determine the formula of the hydrate.

Unit B.2 Stoichiometry (5 Note quiz questions – short w/ lots of practice)

Stoichiometry 2 parts for this unit Analytical / gravimetric stoichiometry Determine the formula from data Solids & gas stoichiometry Stoichiometry Determine the amount of products produced Determine the amount of reactants needed Do you have enough of both? LOTS of ways of doing it FIND ONE THAT WORKS FOR YOU! ALL MUST HAVE A BALENCED EQUATION

Balancing S8 + H2 → H2S Do an atom inventory Subscripts apply to what is INFRONT of them H2O Mg(NO3)2 Coefficients apply to what is BEHIND them 2 H2O 6Mg(NO3)2 S8 + H2 → H2S

Balancing Change ONLY the coefficients to INCREASE numbers of each element so that the Rxts = Prod. S8 + H2 → H2S

Tips CuNO3 + Al → Al(NO3)3 + Cu H2SO4 + NaOH → H2O + Na2SO4 Keep polyatomic ions together! If water and hydroxide (OH-) are present write water as HOH CuNO3 + Al → Al(NO3)3 + Cu H2SO4 + NaOH → H2O + Na2SO4

Tips Save anything elemental for last S8 + O2 → SO3

Tips If stuck double EVERYTHING C8H18 +O2 → CO2 + H2O

KNOW

Balancing Chemical Equations

THIS IS A SKILL You will get better with PRACTICE GO ONLINE Find practice in your packet FRQ 1982 Do the handout

SAMPLE PROBLEM 1 C3H8 + 5 O2 → 3 CO2 + 4 H2O C3H8 + O2 → CO2 + H2O Calculate the mass of oxygen that will react completely with 96.1 grams of propane Write a reaction Balance it 1 C3H8 + 5 O2 → 3 CO2 + 4 H2O C3H8 + O2 → CO2 + H2O

B.2 Note Quiz Questions 1. 2. 3.

SAMPLE PROBLEM 1 C3H8 + 5 O2 → 3 CO2 + 4 H2O C3H8 + O2 → CO2 + H2O Calculate the mass of oxygen that will react completely with 96.1 grams of propane 3. Determine number of moles 4. Determine number of moles of product 1 C3H8 + 5 O2 → 3 CO2 + 4 H2O C3H8 + O2 → CO2 + H2O

1.) Dimensional analysis Calculate the mass of oxygen that will react completely with 96.1 grams of propane 1.) Dimensional analysis START WITH A PLAN […] moles A to moles B […] The plan becomes the top of you chart, previous units become your bottom

1.) Dimensional Analysis C3H8 + 5 O2  3 CO2 + 4 H2O

Calculate the mass of oxygen that will react completely with 96 Calculate the mass of oxygen that will react completely with 96.1 grams of propane 2.) mole map

2.) mole map C3H8 + 5 O2  3 CO2 + 4 H2O

3.) Round about C3H8 + 5 O2  3 CO2 + 4 H2O Find moles Place moles under BALANCED equation Going up divide, moving down multiply C3H8 + 5 O2  3 CO2 + 4 H2O Calculate the mass of oxygen that will react completely with 96.1 grams of propane

4.) Renee’s Table  Equation C3H8 5 O2 3 CO2 4 H2O Moles Conversion Calculate the mass of oxygen that will react completely with 96.1 grams of propane 4.) Renee’s Table MAGIC Equation C3H8 5 O2  3 CO2 4 H2O Moles Conversion Given/wanted

B.2 Note Quiz Questions 4. 5.

Unit B.3 Limiting Reagents/Reactants

Limiting Reagents What limits how many hot dogs everyone can have?

Limiting Reagents The reactant that is consumed first, limiting the amount of product that can be formed Required you to do the problem twice (maybe thrice) Determine the amount of product that each reactant can form

Practice

B.3 Note Quiz Questions 1. 3. 2.

Yields Theoretical Yield Experimental Yield The amount of reactant/product from the stoichiometry math Expectation The amount of reactant/product from an EXPERIMENT Reality

Why Typically because of human error Products are not dry Loss from splatter/spills Residue in transfers Imperfect conditions

%𝑦𝑖𝑒𝑙𝑑= exp𝑒𝑟𝑖𝑚𝑒𝑛𝑡𝑎𝑙 𝑠𝑡𝑜𝑖𝑐ℎ𝑖𝑜𝑚𝑒𝑡𝑟𝑦 ×100 Percent Yield %𝑦𝑖𝑒𝑙𝑑= exp𝑒𝑟𝑖𝑚𝑒𝑛𝑡𝑎𝑙 𝑠𝑡𝑜𝑖𝑐ℎ𝑖𝑜𝑚𝑒𝑡𝑟𝑦 ×100 How much you produced In a perfect world = 100% (it’s never 100% -- reality sucks)

Practice 2AgCl + Cu  CuCl2 + 2Ag A student performs the reaction above with 0.932g Cu, if 2.98g Ag is captured, what is his percent yield? Another student captured 3.4 g of Ag, what is her percent yield?

B.3 Note Quiz Questions 4. If a student carries out the reaction of benzene with nitric acid seen to the left, and from 7.8g of benzene obtained a 33% yield what mass of water did they produce? a. 0.3g b. 0.6g c. 1.2g d. 1.8g 5.

Lab Next Period, Test after that Quiz Write a balanced equation Determine the moles of product from quantities of a gas Determine the LR Percent by mass Excess of remaining Predict change due to error Lab Determination of the formula of a hydrate BEFORE LAB: Do prelab Watch lab procedure