Orgo I Lab Final Exam & Lab Practical Review PDF

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Summary

Review of all topics that were to be covered on the Orgo I lab exam. Includes questions, answers and explanations. Pictures and diagrams taken from lab PowerPoints to assist with understanding. Some answers may be incorrect - but most are the exact same as what was on the actual final. ...

Description

Lab Exam Review I. II. III.

I.

Practical = 50 points Written = 100 points Bonus Quiz (optional) - Will replace two lowest quiz grades

PRACTICAL A. Analyze an Unknown 1. Given an unknown - Given a table of standards, their MP & solubility - Must analyze unknown using the given standards. 2. You must - Take the MP of your unknown & narrow down possible standards it may match - Test the solubility of your unknown in water, acetone and hexane - figure out if your unknown is - Soluble (completely dissolves) - insoluble (none of it dissolves) - partially soluble (some of it dissolves) - May need to test unknown in both hot and cold water, acetone and hexane like in 1st lab 3. Compare unknown to standards - Pick 3 standards from the table that you’ve narrowed down - Run a TLC plate - 3 spots with 3 standards + 1 spot with unknown - reference spot not needed - Develop your TLC plate in the developing chamber given (containing methylene chloride) - Mark the solvent front 1 inch from the top - Look at it under UV and calculate your Rf values - Report your unknown

R

f

of compound =

distance compound traveled from origin solvent front

Some Things to Remember: -

General rule of solubility - “like dissolves like” Methylene chloride is moderately polar (not too much or too little, which makes it the best separation solvent) Least to greatest polarity: Hexane < Acetone < Water

Left to right: soluble, insoluble, partially soluble

B. Setup of Fractional Distillation 1. Fractional distillation will be set up at the front - Come up and identify 5 or more things wrong with the setup - Some things that may be wrong are: - Hickman head cap left off - Missing aluminum block on the hot plate - Glassware put together in wrong order - Make sure thermometer is placed in the correct place - Water goes in the bottom and out the top

Order of setup: Hot plate > Aluminum block > Round bottom flask > Fractional column > Hickman head > Water condenser Thermometer stops at bottom of Hickman head Fractional setup should be wrapped in foil for better insulation Make sure O-ring and black caps are between glassware

II.

-

Written Exam A. T/F Questions TLC plates are always best developed in MeCl2 False It is impossible to differentiate stereoisomers of 2,3 dibromosuccinic acid using IR spectroscopy True

-

IR spectroscopy helps to distinguish enantiomers False

-

IR is commonly linked to a chirality detector False

-

One functional group gives only 1 peak in IR False

-

A reflux ring (not o-ring) is used between pieces of glassware for a better real False

-

A typical SN2 reaction happens in 2 steps False

-

A typical SN1 reaction happens in 2 steps True

-

When recrystallizing trans-stilbene 100% recovery is ideal False

-

The injection port in GC is heated True

-

TLC plates are always best to develop in methylene chloride False

.

Extra T/F Questions that *may* be asked (taken from quizzes) -

A racemic mixture has optical activity False

-

Bromination of maleic acid forms meso 2,3-dibromosuccinic acid False

-

Bromination of fumaric acid forms racemic 2,3 dibromosuccinic acid

False -

You should always seal your distillation system completely to prevent loss of product through evaporation False

-

When mixing water with methylene chloride, methylene chloride will be on top False

-

When an aqueous layer and an organic layer are present in a mix, the organic layer is always at the bottom False

-

When performing recrystallization, cooling the solvent too fast traps impurities True B. Multiple Choice & Open Ended Questions

MC - How does Refractive Index work? Measured by bending of light and change in velocity is measured by refractive index RI MC- Distillation Separation of 2 chemicals by BP MC - What is the best way to separate mixture of 2 organic mixtures with boiling points more than 40 degrees apart Simple distillation OPEN - Simple vs. Fractional Simple - fast but not good with close BPs (have to be at least 40 degrees apart) Fractional - good for close BPs, but slower due to fractional column OPEN - Na2SO4 magnesium sulphate A drying agent; in common w/ other drying agents that are made of anhydrous, inorganic salts OPEN - Reflux; definition & setup

-

Reflux: Gently boil to prevent solvent from being lost due to evaporation during heating Know the purpose of water condenser Reflux technique used to prevent loss by heating Setup drawing (may need to draw/label on exam)

OPEN - What is transfer of solute from one solvent to another? Extraction

OPEN - What do IR peaks correspond to? Molecular vibrations OPEN - A carcinogen: Cause cancer MC - Pick which lab safety rule is incorrect Only store bookbags on benches to keep it out of the way in case of chemical spills OPEN- During extraction, what is the purpose of venting? To release excess pressure MC - In extraction, constant K is Distribution coefficient OPEN - During extraction, how do you determine which layer is organic or aqueous? Add a drop of water to see which layer it goes into. Water belongs in the aqueous layer. MC - Which is not true of IR? It works on all compounds/samples (true- not all samples can be analyzed w/ IR) MC - What is true of IR? It is fast Used on solids, liquids Measures molecular vibrations Cannot distinguish between enantiomers and diastereomers MC - Which is true with GC? GC peaks correspond to retention times MC - What are drying tubes used for? Used to control/absorb odor and moisture MC - What is the purpose of recrystallization To purify samples

MC - Hexane and toluene have BP difference of 40 C to separate them you use to separate? simple

OPEN - Where does each type of waste go? Chemical

Waste Container

Hexane

Organic

Dichloromethane

Halogenated

Sulfuric Acid

Acid

2-Chlorobutane

Halogenated

95 Ethanol

Organic

OPEN - Circle what these solvents are miscible with:

Chemical

Miscible With

Pentane

Dichloromethane

Hexane

Water

Ethanol

Aqueous Solutions

Methylene Chloride (MeCl2)

Dichloromethane

Hexane

Acetone

Ethanol

Aqueous Solutions

OPEN - IR stands for Infrared spectroscopy OPEN - What are standards used for in TLC? They are used as a reference/comparison and to identify compound presence OPEN - General rule of solubility: Like dissolves like OPEN - TLC stands for: Thin Layer Chromatography

MC - How does the water jacket condenser work? Water goes in through the bottom and out through the top

OPEN - GC stands for Gas Chromatography OPEN - What are halogens? Group 17 - fluorine, chlorine, bromine, iodine OPEN - Give one reason for broad beaks around 3300-3600 on IR spectroscopy OH or hydroxyl group presence (water or alcohol) Ketone at 1700 (if asked) OPEN - What is the difference between crystallization and precipitation? Crystallization is slow and selective Precipitation is fast and non-selective OPEN - Simple vs. Fractional distillation Simple - Good for BP 40 degrees or higher apart; faster. Fractional - Good for closer BP, but takes longer. OPEN - Know the GC setup Be able to label: carrier gas, sample injector, column, column oven, detector and waste

Know that the injection port, which is heated, is where the syringe is sticking out OPEN - How many moles of camphor when it is reduced with the amount of moles of NaBH4 given? 4 moles; 4:1:4 ratio One mole borohydride; 4 moles camphor for 4 moles product

OPEN - Order butane, acetone, methanol, and acetic acid in increasing polarity

Butane, acetone, methanol, acetic acid OPEN - Name and draw 3 vibrational modes

Easiest: Asymmetric, symmetric, scissoring OPEN - SN1 & SN2 SN1 is 2 steps SN2 is 1 step OPEN - Major IR peaks you saw in this class:

O-H, C=O, C-O, C-Br

OPEN - Mechanism for Nucleophilic Substitution 2-methyl-2-butanol > 2-chloro-2-methylbutane (SN1) 1-butanol > 1-bromobutane (SN2) First step is protonation to make OH good leaving group OPEN - Will be given an IR, have to compare it to reference spectrums of camphor and isoborneol Notice ketone peak for camphor, hydroxyl for isoborneol If the IR still has both peaks that mean didn’t fully reduce camphor OPEN - Can HPLC detect Chirality? It can but only if a chiral detector is attached MC - All true about IR except: What is true: separate components, identify chemicals, relatively fast What is false: destroys samples, can be used with solids, liquids, or gases (OPEN) Bonus Question for Extra Credit Based Acid- Base Extraction lab Have a neutral (naphthalene) , basic (ethyl 4-aminobenzoate), and acidic (benzoic acid) What was the purpose of extraction? To separate the mix and extract each compound on it’s own Dissolve all in MeCl2, so all in organic layer Add base (NaOH) >> acidic (becomes Na benzoate) Goes to aqueous layer as salt Separate the two layers, the acid is isolated Neutral + basic composition still in organic layer Add acid (HCl) >> basic compound goes to aqueous layer Becomes a basic salt Neutral compound remains in organic layer Products: neutral (naphthalene) , basic (ethyl 4-aminobenzoate), and acidic (benzoic acid) EXTRA - Thin Layer Chromatography (TLC) Two phases; a stationary phase (TLC plate) and a mobile phase (solvent) EXTRA - Miscibility Miscible (mixes together) & immiscible (can’t mix, ex: water/oil) Layer forms if immiscible EXTRA - Chromatography

HPLC - High Performance Liquid Chromatography GC - gas chromatography Both used for separation EXTRA - Distillation Separation of 2 chemicals by BP

C. Calculations 1. Volume/Volume When the solute is a liquid, sometimes it is convenient to express its concentration in volume/volume percent. v/v % = volume  of solute (mL) x 100 % total volume of solution (mL) Ex: Wine has 12 mL of ethanol per 100 mL of solution. Wine would have how much v/v %? = 12  mL  * 100 % 100 mL = 0.12 * 100 % = 12 % ethanol How many mL of acetic acid should be added to 350 mL water to create 30 % v/v solution? v/v % = volume  of solute (mL) x 100 % total volume of solution (mL) 30 % = 

x

mL

350 mL 350 mL * 30 % = 

x

mL 

*

350 mL

350 mL 105 mL = x 105 mL of acetic acid should be added. 2. Distribution Coefficient (K) Ratio where solvents are immiscible, will be given K, mL water, total amount of caffeine Multiple extractions better; more is extracted K = 4.6, 52 mg caffeine, 2 mL water, 2 mL MeCl2

Solute in organic phase/solute in aqueous phase Will have to calculate how much caffeine in each layer K = solute  in organic phase = solubility  in MeCl2 solute in aqueous phase

solubility in water

K > 1 - solute prefers organic K < 1 - solute prefers aqueous 3. Percent Yield: Limiting Reagent, Theoretical Yield and Percent Yield Calculations -

Convert everything to moles (will be given liquid so use density = m/v to find mass) Whichever has less amount of moles is limiting reagent Is it 1:1 mole ratio? Multiply limiting reagent w/ molecular weight for theoretical yield Percent yield = (weight of product/ theoretical yield) x 100 %

Example: Will be given a different problem on the exam 30g of C3H8 burns in the air to produce 70g of CO2. Calculate theoretical and percent yield of CO2. 30 g C3H8 x 1 mol C3H8

x 3 mol CO2 

44 g C3H8

1 mol C3H8

x

44  g CO2 

= 90 g CO2 (TY)

1 mol CO2

Percent yield = 70  g CO2  x 100 % = 77.78 % 90 g CO2 4. Percent Recovery A student obtains 1.5 g of final product from an initial amount of 2 g. Calculate percent recovery. Percent Recovery = amount  of final product x 100 % amount of original material Percent Recovery = 1.5  grams x 100 % 2.0 grams = 0.75 grams x 100 % = 75 %

Bonus Quizzes Unsaturation lab KMnO4/Potassium permanganate used to test for: Double bonds, triple bonds, carbonyl Lucas test is cloudy for what alcohol? Secondary and tertiary Addition Reaction/ Lab 9 Endo is bottom side attack Exo is top side attack Borneol and isoborneol are diastereomers Draw the meso 2,3 dibromobutane compound

Major functional groups expected to see on IR of 2,3 dibromobutane C=O C-Br C-O O-H OH is poor leaving group, so first protonation by H+ First step in substitution with alcohols is protonation to make OH good leaving group 2-methyl-2-butanol undergoes SN1 > 2-chloro-2-methylbutane 1-butanol - SN2 > 1-bromobutane Why do we use GC in nucleophilic substitution lab? Qualitative - what compound it is Quantitative - tells how much of that compound is present

How do maleic and fumaric acid differ? Stereoisomers One cis & one trans HPLC & GC Used for separation Why is forerun discarded? Impurities What is reflux? Heat w/ gentle boil K2 Column lab Ferrocene eluted first in hexane b/c non-polar Acetone added to elute acetylferrocene Will be given a percent composition problem 30 mg final ferrocene 20 mg final acetylferrocene Initially 50 mg product Percent Composition = part x 100 % whole = 30   x 100 % = 60 % ferrocene 50 = 20   x 100 % = 40 % acetylferrocene 50 Which is the best solvent to use for TLC? The one w/ most difference in Rf values Polarity Trans-stilbene (least polar) 9-fluorenone (moderately polar) Benzoic acid (most polar) Reference spots on TLC used for: Control, make sure it doesn’t react, have a standard to compare to Caffeine dissolves/more miscible with MeCl2 and not water

Extraction Add acid to regenerate insoluble acidic compound If basic is present in organic layer, add acid BONUS QUIZ 1. Potassium Permangate test screens what ALL OF THE ABOVE 2. What is meant by endo attack – bottom 3. Borneol and isoborneol related – diastereomers  4. Draw structure of meso 2,3 dibromosuccinic acid –

5. Lucas test gives cloudy result in what? Secondary and Tertiary. B AND D 6. Major function groups in IR of 2,3, dibromosuccinic acidC=O ➢ C-Br ➢ C-O ➢ O-H 7. What is the first step of the nucleophilic substitution of 1 butanol or 2 methyl – Protonation of H+ 8. 1-butanol – Sn2 2-methyl – Sn1 9. Why use GC as an Analytical technique – qualitative; identify the compound, quantitative; how much of the compound

10. How are fumaric and maleic acid different – stereoisomers, diastereomers 11. General purpose of HPLC – Separation 12. What does reflux – gently  boiling/bubbling heat. 13. Distillation why is forerun discarded – impurities 14. Which eluted first ferrocene or Acytle ferrocene - ferrocene because it was the same polarity as the first mobile phase (hexane) then used Acetone to push out the other one 15. Calculate percent composition ferrocene and acytle ferrocene 30/50 20/60 16. Which TLC result are point to the best solvent – Methylene ChlorideDifferent Rf values 17. Label Trans stilbene(least), 9-flourone(moderate polarity), benzoic acid(most) by polarity 18. Reason for using a reference – all the above 19. What do you add to an acid compound to reform it back to its water insoluble form – moreAcid 20. When a basic compound is present in the organic layer what must be added before extracting can occur – add Acid 21. Caffeine is more soluble in water or methylene Chloride....