Organic Chemistry: Lab Quiz 1

Experiments 1-5

Experiment 1, oyster-shell demineralization: What was the purpose of treating crushed oyster shell with HCl?

To selectively dissolve the inorganic CaCO3 mineral, leaving the mostly insoluble organic matrix behind for isolation and testing.

Experiment 1, oyster shells: What two types of material make up the shell, and how does each contribute to its toughness?

The shell contains inorganic CaCO3 and a small organic biopolymer matrix. CaCO3 provides compressive strength; the organic matrix organizes crystal growth and provides tensile toughness.

Experiment 1, oyster shells: Write the reaction that occurs when CaCO3 reacts with HCl, and name the visible sign of this reaction.

CaCO3(s) + 2 HCl(aq) -> CaCl2(aq) + H2O(l) + CO2(g). The released CO2 causes bubbling.

Experiment 1, oyster shells: Why must HCl be added slowly and why must the reaction vessel stay unsealed?

The reaction can be vigorous and releases CO2 gas. Slow addition controls bubbling and splashing; an unsealed vessel prevents pressure buildup.

Experiment 1, oyster shells: Why was water added to the crushed shell before adding HCl?

Water moderates the acid-carbonate reaction.

Experiment 1, oyster shells: After acid treatment and filtration, what is in the filtrate and what is the residue?

The filtrate contains soluble CaCl2(aq) and possibly excess HCl. The residue is the mostly insoluble organic matrix.

Experiment 1, oyster shells: Why does filtration separate the organic matrix from the calcium-containing material after HCl treatment?

HCl converts solid CaCO3 into soluble CaCl2, while the organic matrix remains an insoluble solid.

Experiment 1, oyster shells: Why is the isolated organic residue rinsed with water and then dried before weighing or testing?

Water removes dissolved HCl and CaCl2. Drying removes solvent so the mass and qualitative tests represent the residue rather than leftover solution.

Experiment 1, oyster shells: Why might the residue be rinsed briefly with ethanol, and why should it be cooled in a desiccator before weighing?

Ethanol can speed drying because it evaporates readily. Cooling in a desiccator prevents the dry sample from absorbing atmospheric water before it is weighed.

Experiment 1, oyster shells: How can CaCO3 be re-formed from the CaCl2 filtrate?

Add Na2CO3 solution to form insoluble CaCO3(s), then filter, dry, and weigh the precipitate.

Experiment 1, oyster shells: What does the ninhydrin test detect, what is a positive result, and why is heating used?

Ninhydrin detects free primary amines and many amino acids. Purple or blue-violet is positive. Heating helps the color-producing reaction develop.

Experiment 1, oyster shells: What does the Biuret test detect, and what result indicates protein or longer peptides?

It detects peptide bonds. A violet or lavender result indicates proteins or longer peptides.

Experiment 1, oyster shells: Why were positive and negative controls used for the ninhydrin and Biuret tests?

A positive control confirms the reagent and procedure can give the expected signal; a negative water control shows that a color change is not caused by the reagent or water alone.

Experiment 1, oyster-shell demineralization: What were the roles of the beaker, stirring, filtration, and drying in the workflow?

The beaker held the shell-water-acid reaction; stirring exposed mineral surfaces to acid; filtration isolated insoluble organic residue from soluble salts; drying removed water before mass measurement and qualitative testing.

Experiment 1, oyster shells: Why is vacuum filtration preferred for isolating the organic residue?

A vacuum pulls liquid through filter paper faster than gravity filtration, leaving the insoluble organic residue on the paper.

Experiment 1, oyster shells: Why should the residue be rinsed until near-neutral by pH paper?

It verifies that most excess HCl has been removed, so remaining acid does not affect the residue's mass or later qualitative tests.

Experiment 1, oyster shells: Why should shell pieces be crushed into small chips but not fine powder?

Small pieces provide surface area for reaction. Avoiding fine powder reduces inhalation risk and makes handling and filtration easier.

Experiment 2, organic structure: How many covalent bonds does a neutral carbon normally have, and how are double and triple bonds counted?

Carbon normally has four total bonds. A double bond counts as two bonds and a triple bond counts as three.

Experiment 2, organic structure: Compare empirical, molecular, structural, condensed structural, and line-angle formulas.

Empirical gives the simplest whole-number ratio; molecular gives the actual atom count; structural shows connectivity; condensed abbreviates connectivity; line-angle uses line ends and vertices for carbon atoms.

Experiment 2, isomerism: What is the difference between constitutional isomers and stereoisomers?

Constitutional isomers have the same molecular formula but different connectivity. Stereoisomers have the same connectivity but a different three-dimensional arrangement.

Experiment 2, isomerism: Distinguish skeletal isomerism from positional isomerism.

Skeletal isomers have different carbon skeletons or branching. Positional isomers have the same skeleton and functional group or substituent, but it is attached at a different position.

Experiment 2, geometric isomers: Why can an alkene show cis/trans isomerism, and what condition is required?

A C=C double bond cannot freely rotate. Each alkene carbon must have two different groups attached for distinct geometric isomers to exist.

Experiment 2, functional groups: What is a functional group?

A characteristic arrangement of atoms that gives an organic molecule a recognizable class of chemical behavior.

Experiment 3, IR spectroscopy: What does IR spectroscopy measure, and why can it identify functional groups?

It measures absorption of infrared radiation at different wavenumbers. Bonds vibrate at characteristic frequencies, producing recognizable absorption regions.

Experiment 3, IR spectroscopy: What is IR most useful for in this course?

Identifying functional groups and using them to help characterize an unknown compound's structure.

Experiment 4A, TLC: What are the stationary and mobile phases, and how does each function?

The stationary phase is polar silica gel on the plate. The mobile phase is the solvent that rises by capillary action and carries compounds upward.

Experiment 4A, TLC on silica: How do compound polarity and solvent polarity affect how far a spot travels?

With the same solvent, polar compounds bind silica more strongly and travel less; nonpolar compounds travel farther. A more polar solvent competes better with silica and generally moves spots farther.

Experiment 4A, TLC: What does an Rf value mean, and how is it calculated?

Rf describes relative movement on a plate: distance traveled by the compound divided by distance traveled by the solvent front. It has no units.

Experiment 4A, TLC: What does one spot versus multiple spots in a sample lane tell you?

One spot suggests one detectable component under those conditions. Multiple spots show that the sample contains multiple components.

Experiment 4A, TLC: Why should an unknown and known reference compounds be spotted on the same plate?

Their Rf values and positions can be compared under exactly the same solvent, plate, and development conditions.

Experiment 4A, TLC setup: Why must the sample spots start above the solvent level in the developing jar?

If the spots are submerged, the samples dissolve into the solvent reservoir instead of being carried upward on the plate.

Experiment 4A, TLC setup: Why should spots be small, concentrated, and applied with separate capillary tubes?

Small spots give sharper separation and more accurate Rf values. Separate capillaries prevent cross-contamination between samples.

Experiment 4A, TLC setup: Why are the baseline and solvent-front marks made in pencil rather than ink?

Ink can dissolve and travel with the solvent, creating misleading spots. Pencil graphite does not dissolve this way.

Experiment 4A, TLC setup: Why should you avoid touching the plate's front surface?

Skin oils and other organic residues contaminate the silica and can create unexpected spots.

Experiment 4A, TLC setup: Why must the plate sides not touch the walls of the developing jar?

Contact can disrupt or unevenly wick the solvent, producing a distorted solvent front and unreliable Rf values.

Experiment 4A, TLC development: What is the purpose of the capped jar and filter-paper wick?

They saturate the chamber with solvent vapor and promote more even solvent development.

Experiment 4A, TLC development: Why remove the plate at the solvent-front line and mark the solvent front immediately?

The solvent-front distance is needed to calculate Rf. If the solvent runs off or evaporates before marking, the measurement becomes unreliable.

Experiment 4A, TLC troubleshooting: Why might the bottom corners of a plate be trimmed before repeating a TLC?

Trimming can help the solvent enter the plate more evenly if the original solvent front was uneven.

Experiment 4A, TLC visualization: Why are plates viewed under 254 nm UV light, and what types of molecules show best?

UV-active compounds quench the fluorescent plate background and appear dark. Compounds with substantial pi-bond conjugation often show well.

Experiment 4A, TLC: Give two advantages and one limitation of TLC.

It is fast, inexpensive, simple, and works with many nonvolatile solids or liquids. Its major limitation is that it is mainly qualitative, not a reliable measure of quantity.

Experiment 4A, ink TLC: What was the point of separating inks with methanol?

To show that an ink can contain multiple dyes and that the dyes' movement reflects their differing interactions with silica and the polar methanol solvent.

Experiment 4B, TLC stains: Why would you use a chemical stain after spotting a TLC plate rather than only UV light?

A chemical stain can reveal a functional group or a compound that is not sufficiently UV-active to see under the UV lamp.

Experiment 4B, TLC stains: What does ninhydrin detect and what step develops the visible result?

Ninhydrin detects amines. After spraying it on the plate, heating with a heat gun develops the colored product.

Experiment 4B, TLC stains: Why did the ninhydrin procedure not require eluting the plate in a solvent jar?

The goal was to test the functional groups of the already spotted compounds at their original locations, not to separate them first.

Experiment 4B, TLC stains: How can ninhydrin make fingerprints visible?

Fingerprints leave organic residues, including amino-containing compounds, that react with ninhydrin and reveal the ridge pattern after development.

Experiment 4C, Solubility I: What do miscible and immiscible mean?

Miscible liquids mix into a single phase; immiscible liquids do not mix and form separate phases or layers.

Experiment 4C, Solubility I: How do polarity and hydrocarbon-chain length generally affect a molecule's solubility in water?

Greater polarity and ability to interact with water generally increase solubility. A longer nonpolar hydrocarbon chain generally decreases solubility.

Experiment 4C, Solubility I: Why were equal water volumes used and samples observed both before and after stirring?

Equal water volumes make comparisons fair. Observing before and after stirring distinguishes a liquid that truly dissolves from one that remains a separate layer or suspension despite mixing.

Experiment 4C, Solubility I: What were the roles of the graduated cylinder, test tubes, dropper bottles, and test-tube rack?

The graduated cylinder measured a consistent water volume; each test tube held one water-compound mixture; droppers added comparable amounts of liquids; the rack kept tubes upright and organized for comparison.

Experiment 4C, Solubility I: What was the purpose of adding repeated 20-drop portions up to a maximum of 100 drops in the chain-length comparison?

To find the approximate amount needed to reach the solubility limit for each compound while using the same water volume.

Experiment 4C, Solubility I: Why were heptane- and toluene-containing solutions placed in organic waste?

They are organic solvents and are not safe for sink disposal.

Experiment 5A, steam distillation: What was the purpose of the experiment?

To isolate a volatile, water-insoluble essential oil from plant or spice material by steam distillation.

Experiment 5A, steam distillation setup: What are the roles of the blender, powder funnel, and round-bottom flask?

The blender makes a water-containing plant slurry; the powder funnel transfers the slurry with less loss; the round-bottom flask holds the slurry while it is heated and distilled.

Experiment 5A, steam distillation setup: What are the roles of the heat source, distillation head or Claisen adapter, condenser, and receiver?

The heat source produces vapor; the Claisen adapter directs vapor into the apparatus; the condenser cools vapor back to liquid; the receiver collects the liquid distillate.

Experiment 5A, steam distillation setup: Why is the condenser essential?

It removes heat from the vapor so volatile water and essential-oil components condense into a liquid that can be collected.

Experiment 5A, steam distillation setup: Why was a 50 mL graduated cylinder used as the receiver?

It collects the distillate and lets you monitor the collected volume while also holding ice and NaBr for separation.

Experiment 5A, steam distillation: Why were the temperatures of the first and last drops of distillate recorded?

They document the temperature range over which distillation occurred and help characterize how the mixture distilled.

Experiment 5A, steam distillation: What is a natural product and what is an essential oil?

A natural product is a compound made by a plant or animal. An essential oil is a volatile mixture of characteristic plant compounds responsible for fragrance or flavor.

Experiment 5A, steam distillation: Why can limonene be distilled below 100 C even though pure limonene boils near 178 C?

Water and limonene are immiscible and each contributes its own vapor pressure. Their combined vapor pressure reaches atmospheric pressure at a lower temperature than either pure liquid's normal boiling point.

Experiment 5A, steam distillation: State the pressure relationship that explains the lower boiling temperature.

Ptotal = Pwater + Pwater-insoluble compound. This is an application of Dalton's law of partial pressures.

Experiment 5A, steam distillation: Why is the lower distillation temperature especially helpful for essential oils?

It reduces the chance that heat-sensitive natural products will thermally decompose.

Experiment 5A, steam distillation: Why were the plant materials ground, torn, or blended with water before heating?

Breaking up the plant material increases surface area and helps release essential oil into the water-containing slurry.

Experiment 5A, steam distillation: What is the purpose of ice in the receiving cylinder?

It cools the distillate and limits loss of volatile essential-oil components.

Experiment 5A, steam distillation: Why was NaBr added to the distillate?

NaBr salts out the oil: it makes the water layer more polar and denser, reducing the organic oil's water solubility and improving layer separation.

Experiment 5A, steam distillation: Which layer was collected as the essential oil, and why was the vial pre-tared?

The top oil layer was collected. A pre-tared vial lets you determine oil mass by subtracting the empty vial mass.

Experiment 5A, steam distillation safety: What should you do if the slurry foams toward the condenser, and why?

Move the heat source away to reduce heating and prevent slurry from entering and contaminating the condenser.

Experiment 5A, steam distillation safety: Why should the apparatus cool before you disassemble it?

Hot glass can burn you and can break more easily if handled or temperature-shocked.

Experiment 5A, terpenes: What are terpenes and terpenoids?

Terpenes are natural compounds assembled from five-carbon isoprene units. Terpenoids are terpene-related compounds that also contain oxygen.

Experiment 5A, carvone enantiomers: Why can R- and S-carvone have different smells even though they have the same formula and connectivity?

They have different three-dimensional shapes, so they interact differently with chiral odor receptors.

Experiment 5B, Solubility II: How does temperature affect the solubility of salicylic acid in water in the demonstration?

Heating increases its solubility. As the hot solution cools slowly, dissolved salicylic acid may crystallize back out.

Experiment 5B, Solubility II: What was the point of treating salicylic acid with base?

The base deprotonates the carboxylic acid to form an ionic salicylate salt, which is much more water-soluble.

Experiment 5B, Solubility II: Write the acid-base equation for salicylic acid reacting with NaOH.

Salicylic acid + NaOH -> sodium salicylate + H2O. The carboxylic-acid proton is transferred to hydroxide, leaving a negatively charged carboxylate paired with Na+.

Experiment 5B, Solubility II: What happens if HCl is added to an aqueous sodium-salicylate solution?

HCl protonates salicylate back to neutral salicylic acid, which is much less water-soluble and can precipitate as a white solid.

Experiment 5B, Solubility II: Write the reaction of diisopropylamine with HCl.

(i-Pr)2NH + HCl -> (i-Pr)2NH2+ Cl-. The neutral amine accepts H+ to become an ionic ammonium salt.

Experiment 5B, Solubility II: Why were NaOH, NH4OH, and NaHCO3 compared with salicylic acid?

They are bases of different strengths. Each can deprotonate acidic salicylic acid to some extent, letting the demonstration connect acid-base chemistry to ionization and water solubility.

Experiment 5B, Solubility II: In the temperature demonstration, what are the roles of the hot-water bath and boiling stick?

The hot-water bath heats the salicylic-acid mixture more gently and evenly. The boiling stick promotes smooth boiling and reduces bumping.

Experiment 5B, Solubility II: What happens when an amine such as diisopropylamine is treated with acid?

The amine is protonated to form an ionic ammonium salt, which is more water-soluble than the neutral amine.

Experiment 5B, Solubility II: Why does acid-base ionization often increase an organic compound's water solubility?

It converts a neutral covalent molecule into ions, which have strong ion-dipole interactions with polar water.

Experiment 5B, Solubility II: At what pH is a carboxylic acid more soluble, and at what pH is an amine more soluble?

A carboxylic acid is more soluble at basic pH because it is deprotonated. An amine is more soluble at acidic pH because it is protonated.

Lab safety, TLC: Why must you not look directly at the short-wave UV lamp?

Short-wave UV radiation can damage your eyes.

IR spectroscopy lecture: What is spectroscopy, and what does absorption spectroscopy measure?

Spectroscopy is a technique used to help determine a compound's structure. Absorption spectroscopy measures how much light a sample absorbs as a function of wavelength.

IR spectroscopy lecture: What does an IR spectrometer probe, and what structural information does this give?

It probes molecular bond vibrations. The resulting absorption frequencies help identify functional groups.

IR spectroscopy lecture: Why is IR described as largely nondestructive?

It usually consumes or destroys little to no sample while measuring its absorption spectrum.

IR spectroscopy lecture: What is frequency, what is wavelength, and how are they related?

Frequency is the number of wave cycles passing a fixed point per second; wavelength is the distance between successive peaks or troughs. They are inversely proportional.

IR spectroscopy lecture: What causes atoms connected by a bond to vibrate after the bond is stretched or compressed?

The bond acts like a spring: a restoring force pulls atoms back toward their equilibrium bond length after stretching or compression.

IR spectroscopy lecture: What are stretching and bending vibrations?

Stretching changes bond length; bending changes the angle between bonds. Both can produce IR absorptions when they interact with IR radiation.

IR spectroscopy lecture: How do atomic mass and bond strength affect an absorption frequency?

Increasing atomic mass lowers the frequency. Increasing bond strength raises the frequency because a stronger bond is harder to stretch.

IR spectroscopy lecture: Why does a stronger carbon-carbon bond absorb at a higher frequency?

A stronger bond is stiffer and requires more energy to stretch, so its vibration occurs at a higher frequency.

IR spectroscopy lecture: How does conjugation affect the IR stretching frequency of a bond such as C=O?

Conjugation lowers the stretching frequency because resonance reduces the bond's effective bond order and makes it less stiff.

IR spectroscopy lecture: What is the fingerprint region, and why is it useful?

The fingerprint region is roughly 600-1400 cm^-1. It contains many complex absorptions that make a molecule's overall spectrum highly distinctive.

IR spectroscopy lecture: Where is the functional-group region, and how is it used?

About 1600-3500 cm^-1. Absorptions there are often characteristic of particular functional groups and are used for initial identification.

IR spectroscopy lecture: Why do enantiomers have the same ordinary IR spectrum?

Enantiomers have the same bonds and vibrational energies in an achiral IR measurement, so they give the same IR absorptions.

IR spectroscopy lecture: How does hybridization affect C-H stretch frequency?

More s character makes the C-H bond stronger, so C-H stretching frequency follows sp > sp2 > sp3.

IR spectroscopy lecture: What is a reliable order for analyzing an unfamiliar IR spectrum?

First look outside the fingerprint region for unusual functional-group peaks. Identify strong diagnostic features such as O-H, N-H, C=O, C=C, or aldehydic C-H, then use the full spectrum and structure constraints together.

IR spectroscopy lecture: What are IR's main strengths and limitations for structure determination?

IR usually identifies which functional groups are present or absent, but IR alone rarely determines an entire structure because some signals are ambiguous. Matching a known sample's spectrum can confirm identity.

IR spectroscopy lecture: What is meant by sigma-bond and pi-bond stretching in IR?

They are bond-stretching vibrations. Sigma bonds such as C-H give characteristic stretches, while pi bonds such as C=C and C=O often provide especially useful functional-group signals.