What happens if a melting point capillary has too much sample?
Excess sample can lead to inaccurate melting point determination, difficulty in observing melting, capillary breakage, and contamination of the apparatus. It can cause broader melting ranges and make it challenging to identify the true melting point.
What layer would a species (inorganic, organic polar, organic non-polar…) be in a separatory funnel?
organic non-polar species will be in the organic layer
organic polar species may distribute between the organic and aqueous layers depending on their polarity
inorganic species will typically remain in the aqueous layer
What layer would an acid or base be in a separatory funnel with an organic solvent-aqueous acid vs. organic solvent-aqueous base?
In a separatory funnel with an organic solvent and aqueous acid, an acidic compound will be protonated and become water-soluble, moving into the aqueous layer.
In a separatory funnel with an organic solvent and aqueous base, a basic compound will deprotonate and become more soluble in the organic layer.
What would cause a low melting point?
Incomplete recrystallization, or the presence of solvent molecules trapped within the crystal lattice.
What if crystals do not form in a recrystallization?
If crystals do not form during recrystallization, it may indicate that the solute concentration is too low, the solution is too hot, or the cooling process is too rapid. Adjusting these parameters or employing a different solvent system may help promote crystal formation.
What if too much drying agent is used? Or the wrong one?
Excessive loss of product or solvent retention in the drying agent. Using the wrong drying agent may result in incomplete drying or chemical reaction with the compound. Both scenarios can affect the purity and yield of the final product.
What is the best way to measure reagents? 1 mL of a liquid? 10 mL? 0.01 g of a solid?
The best way to measure reagents depends on the accuracy required for the experiment. For liquids, volumetric pipettes or graduated cylinders are suitable for precise measurements. For solids, analytical balances are used to measure mass accurately.
Can you analyze a stoichiometry problem and identify where a student has made a mistake?
Common mistakes include incorrect conversion factors, failure to balance chemical equations, and misinterpretation of the given data. By carefully reviewing each step of the problem-solving process, we can pinpoint and correct any errors.
How would you purify 40 mg of a solid that has a by-product present?
One method to purify a solid with a by-product present is recrystallization. First, dissolve the mixture in a suitable solvent at an elevated temperature. Then, cool the solution slowly to allow the desired compound to crystallize out while leaving impurities in solution. Filtration or centrifugation can be used to separate the crystals from the solution. Washing the crystals with a small amount of cold solvent can further purify them.
How would you purify 4 g of a solid that is 95% pure?
If the solid is already 95% pure, further purification may not be necessary. However, if higher purity is desired, techniques such as recrystallization or column chromatography.
How would you purify 40 mL of a liquid that is 80% pure?
Distillation is a common method for purifying liquids. In simple distillation, the liquid is heated to its boiling point, and the vapor is collected and condensed into a separate container.
How would you separate two liquids with a 5 °C difference in boiling point if you had only 100 mg? 100 mL?
For a small amount of mixture (100 mg), fractional distillation may not be practical. Instead, simple distillation can be attempted, but the separation may not be as effective due to the small sample size. For a larger amount of mixture (100 mL), fractional distillation would be more effective. The mixture is heated, and the vapors are collected and condensed. The temperature is carefully monitored to ensure that the lower boiling point compound is collected first, followed by the higher boiling point compound. This process is repeated until the desired separation is achieved.
How would you isolate a temperature sensitive extract, present as a 5% component,
from a natural matrix?
To isolate a temperature-sensitive extract from a natural matrix, employ cold extraction methods and low-temperature solvents to minimize degradation. Ensure careful temperature control throughout the process, from extraction to purification, to preserve the integrity of the extract.
Suggest the best apparatus to identify a final product.
* What if you were reducing a C=O to C-OH?
* An unknown solid?
* Isomers of a compound containing the same functional groups?
* A small amount of a reaction mixture to determine a Keq?
Reduction: Fourier-transform infrared (FTIR) spectroscopy can monitor changes in functional groups, while nuclear magnetic resonance (NMR) spectroscopy, specifically proton NMR (^1H NMR), can confirm the formation of the C-OH group by observing changes in chemical shifts and peak patterns.
Unknown solid: X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS), and differential scanning calorimetry (DSC) can be used to determine the crystalline structure, elemental composition, and thermal properties of the solid.
Isomers of a compound: To distinguish between isomers containing the same functional groups, techniques such as nuclear magnetic resonance spectroscopy (^1H NMR, ^13C NMR) and mass spectrometry (MS) coupled with gas chromatography (GC-MS) or liquid chromatography (LC-MS) can provide information about molecular structure, connectivity, and fragmentation patterns, allowing for differentiation between isomers.
Keq: UV-visible spectroscopy or gas chromatography (GC) coupled with mass spectrometry (MS) to monitor changes in reactant and product concentrations over time, allowing for the calculation of equilibrium constants (Keq) based on the initial and final concentrations of species involved in the reaction.
What data comes from FT-IR/ FT-ATR?
information about the functional groups present in a molecule by measuring the absorption of infrared radiation
What data comes from NMR?
information about the molecular structure, connectivity, and environment of atoms within a molecule
What data comes from Gas chromatography (GC)?
Separates and quantifies components of a mixture based on their volatility and interaction with a stationary phase. The data obtained from GC typically includes retention times and peak areas, which can be used to identify and quantify the components present in the sample.
What data comes from Gas chromatography-mass spectrometry?
In GC-MS, after separation by GC, the components are ionized and fragmented in the mass spectrometer, producing mass spectra that can be used for compound identification based on their fragmentation patterns and mass-to-charge ratios.
What data comes from UV spec?
Absorption of UV or visible light by a sample. UV spectroscopy provides information about the electronic transitions that occur within molecules, allowing for the identification and quantification of compounds with conjugated double bonds or chromophores.
