Phy Chem 1 : Practicum 2

What is the difference between a covalent and ionic bond?

A covalent bond shares electrons between atoms, while ionic bonds involve transferring electrons from one atom to another

Explain what electronegativity means, and is O-H polar or nonpolar?

Electronegativity is an atom's tendency to attract shared electrons in a chemical bond. O-H bonds are polar bonds because oxygen is much more electronegative than hydrogen

What are minerals and are they found in nature

Minerals are elements in ionic form and can be found in nature within rocks, oceans, and soil

What is a polyatomic ion?

It is a more than one atom bonded by covalent bonds with a charge

The presence of calcium ions in milk will be detected by the formation of?

Solid calcium oxalate (CaC2O4)-(an insoluble solid collected by filtration) - after adding ammonium oxalate 

When testing for Fe(II) of Fe(III) using K3Fe(CN)6, what color is observed?

Fe (II) is dark blue precipitate, Fe (III) dark green precipitate

How do you calculate the moles and mass of solute needed to prepare a solution of a particular molarity and how do you prepare the solution?

Calculate moles using Molarity = mols solute / L solution, find mass using g solute = molar mass x molarity x L solution. Measure the right amount of solute and solvent and combine.

How do you convert %m/V to molarity?

You turn the %m/V to a ratio  of g / L, and divide by molar mass. 

How do you convert between molarity and osmolarity?

Osmolarity is molarity x # of particles

What is the physiological meaning of a mineral, and how does the abundance of different minerals in the body vary?

There are 21 elements found in the human body in ionic form, which are called minerals. They are very common throughout nature, exist in many of the foods that we eat, and are essential for our bodies to function properly.

What are trace minerals? Are calcium and iron trace minerals?

• When minerals are needed and/or present in the human body in very small amounts (trace minerals)

• Calcium is NOT a trace mineral BUT iron is!

How was the presence of calcium ions in milk found, and what was the important experimental observation associated with its identification?

• by adding ammonium oxalate, if calcium is present, an insoluble precipitate of calcium oxalate (CaC2O4) will form

What anion does calcium combine with physiologically during the formation of bone? How can the same anion lead to pathophysiological vasoocclusion that can compromise blood flow to vital organs?

• Phosphate (PO4)3-

• Excess calcium and/or phosphate in the blood can lead to precipitation of insoluble calcium phosphate, which can lead to vasoocclusion

What hormone controls calcium ion and phosphate metabolism?

• Parathyroid hormone

What are the two forms of iron that are physiologically important? How did we distinguish between them in the lab?

• O2/CO2 transport 

• Fe (II) - Ferrous - Dark blue precipitate; an essential component of RBC protein hemoglobin

•  & Fe (III) - Ferric  - green precipitate

What condition can occur when the body does not have an adequate supply of iron? What are symptoms of this condition?

• Anemia (iron-deficiency anemia)

• SX’s: weakness, fatigue, SOB, most common sx: pallor (paleness or loss of reddish color) of the mucous membranes

What protein within RBCs is iron (II) an essential component of? What is the main function of this protein in the human body?

Hemoglobin - carries oxygen from the lungs to the tissues of the body

Based on the formula alone, how do you predict whether a compound is ionic vs molecular?

• Molecular compound: non-metal & non-metal 

• Ionic compound: non-metal & metal OR transition metal & metal

**Ionic bonds (complete transfer of electrons)- will have one positive ion bonded to a negative ion (ex. NaCl)

Using hexanes requires safety precautions such as gloves, lab coats, eye protection and chemical hoods, true or false?

True

The origin on a TLC plate refers to the

application point of the samples on the plate

The eluent is also known as the stationary phase in TLC testing, true or false?

False

A permanent ink marker can be used to mark the origin or eluent front on a TLC plate, true or false?

False

Inaccurate Rf determinations can result from what?

Allowing the eluent front to evaporate before marking it,  Allowing the eluent level to exceed the origin line when beginning the TLC testing, Inconsistently marking the middle of the sample spot.

Calculating Rf value:

Distance that the substance traveled divided by the eluent line (no unit- it’s a ratio)

What does chromatography rely on to successfully carry out separation of mixtures?

• Relies on uneven distribution of substances that you are testing/are sampled between two immiscible (does not mix together) phases due to the difference in affinity of each substance to two phases. 

• Two phases are: stationary phase and mobile phase. The stationary phase was more polar in our experiment. The mobile phase was less polar in our experiment

What two factors determine or affect the rate of migration of a substance in a chromatographic separation?

• SOLUBILITY in the solvent

• Degree of attraction (or polarity) it has to the paper; more attraction/polarity = move less distance & slower

What manipulations can be performed to change the rate of migration of substances in thin-layer chromatography (TLC)?

Change the polarity of the mobile phase - it will alter the affinity of the substance with the with the stationary phase

What experimental parameter measures the ability of a substance to migrate on a TLC plate under a given set of conditions, how is it measured and what is the significance of its magnitude?

• Retention factor (Rf)

  • Rf = distance traveled by substance (cm)/distance traveled by eluent front (cm) 

• It tells us chromatographic behavior & polarity of the substances 

  • Low Rf = more polar 

  • High Rf = less polar

What can’t an Rf value ever be greater than 1.00?

• The substance cannot move past the point where the solvent traveled; inaccuracy

What can ink be used to mark a TLC plate and why?

• Pencil only; pen will interfere

What errors would result from failure to promptly mark the eluent front on a TLC plate?

• By not having an eluent front (not drawing it after you pull it out of the beaker), you will not have a denominator and you won't be able to calculate your Rf value. It leads to inaccurate calculations for each substance. You cannot classify the substances with their correct polarity.

In the lab, we looked at a reaction between a volatile aldehyde or ketone, and 2,4-dinitrophenylhydrazine. What is the product of that reaction and why is it useful in TLC analysis?

• Decreases volatility

• Makes a colored solid product that can be easily handled and visualized

A compound has an Rf value of 0.50. How far would it have traveled from the origin if the eluent front is at 10 cm? 5 cm?

• 5cm

• 2.5cm

What is the advantage of allowing the eluent front to rise all the way to the top of the paper? Can you speculate what could be a disadvantage or complication?

• To get better separation of components they should run on TLC for a long distance

• Data will be more precise, whereas less distance of eluent front will give less diversity in data and analysis

What is the name of the apparatus used for performing extraction?

Separatory funnel

When performing an extraction it is important to vent the funnel to allow air to enter, true or false?

False

What is extraction useful for?

• Separation of mixtures, Purification of compounds, Removal of impurities from a compound

What is true regarding polar molecules?

They have an unsymmetrical electron distribution, They have two permanent oppositely-charged structural regions, They exhibit moderately strong, They typically are soluble in water

Which contains ALL POLAR functional groups?

alcohol, amine, carboxylic acid

What is the general relationship between water solubility and molecular mass/size?

Higher molecular mass/size, lower solubility

During an extraction, which solvent will be the top layer?

The solvent with the lowest density

Polar/water-soluble molecules have the greatest difficulty crossing the blood brain barrier, true or false?

True

What is the blood brain barrier

It is a semipermeable membrane between the blood and the brain

What is the distribution coefficient (Kd)  of a substance?

It is the ratio of concentrations of solute in each solvent, a ratio that describes how a substance distributes itself between two immiscible phases, such as oil and water, at equilibrium

How long does it take tetrahydrocannabinols (THC) to be eliminated from the body and why?

Many weeks, because they are nonpolar and stay in fat tissue

What is the most efficient way to perform an extraction to maximize the amount of solute extracted?

Multiple extractions

What physical property determines the relative positions of aqueous and organic phases during an extraction?

Density

What is the fastest way to determine which layer is which during an extraction while working in the lab?

Add a small volume of one of the solvents and observe which layer will increase or expand. The one that expands is the one that you added.

What functional groups make a substance more soluble in water? More soluble in lipids?

• Lipid soluble functional groups non-polar--> alkane, alkene (carbon double bond carbon), arene (aromatic ring w/ hydrocarbon), thiol (sulfur and oxygen), sulfide (sulfur), disulfide (two sulfur)

• Water soluble (polar)--> the rest of them. Look at the pages. Alcohol, ester.... Etc.

What is the blood-brain barrier and what are its physical properties and functional characteristics?

Fatty sheath that surrounds the blood vessels of the brain. Non-polar. It is impermeable to water substances. It will not allow polar drugs like penicillin, but it will allow non-polar drugs like anesthetics to enter

How do size and polarity affect the water -solubility of a substance and its ability to be retained in or excreted from the body and/or travel through the blood-bain barrier?

• Polar functional groups, water soluble and smaller in size (lower molar mass). It will go in aqueous compartment like blood. It will be excreted easily by urine/shorter half-life/ less retained

• As size increases (molar mass increases), compounds with non-polar functional groups will be less water soluble. Will go to fatty compartments. They dissolve in fatty tissues à slower eliminated/longer half-life/more retention

What is the distribution/partition coefficient (Kd) of a substance, how is it calculated, and what kind of information can be obtained from the partition coefficient (Kd) of a substance?

• Kd: the ratio of concentrations (mass or moles per unit volume) of solute in two immiscible phases

• Kd= (grams of compound A extracted in organic substance/mL of organic phase)/(grams of compound A remaining in aqueous phase/mL of aqueous phase)

What is the effect of adding more water to the sample of aqueous solution taken for extraction BEFORE the extraction on your calculation of Kd?

• Adding more water to the aqueous phase lowers the concentration of the substance in that phase, allowing for more to be dissolved in the aqueous phase.

• Does not affect the calculation of the Kd, since the substance will naturally distribute itself among the available volumes of the two immiscible solvents such that the ratio of the concentrations reaches the naturally determined value of Kd at that temperature

After extraction with ethyl acetate, a student drained the aqueous layer from the separatory funnel, then rinsed the funnel with 5 mL of ethyl acetate and added it to the organic phase before evaporating the solvent. Her lab partner told her that the additional 5 mL of ethyl acetate would lead to an error in the calculation of Kd. Is this correct?

• This is not correct. The first student actually performed the experiment most efficiently by rinsing the funnel with ethyl acetate because it allows for a maximum yield of crystals. If rinsing is not done, there is some organic layer left in the funnel and therefore wasted, which is costly to the lab.

What are isomers in general, and what are constitutional isomers specifically? 

• Isomers: identical molecular formula; different arrangement of atoms

• Constitutional isomers: same molecular formula; different bonding atom organization/bonding patterns

When representing 3D molecules in 2D, how is 3D special perspective indicated?

• With wedges (towards) & dashed lines (away)

• Straight lines show bonds within the plane 

How are Fisher projections used to represent 3D perspective?

• Horizontal bonds come TOWARDS the viewer

• Vertical bonds point AWAY

What is meant by the “conformation" of an organic molecule?

The 3D spatial arrangement about a single bond

How are cis-trans isomers the same? How are they different?

• They share the same formula and connectivity 

• Differ in spatial arrangement of groups across a ring or double bond 

• CIS; same side 

• Trans: opposite

What are the electronic and molecular geometries around sulfur in sulfite?

• Electronic Geometry  (EG): [ONLY 3]: # of clouds: Tetrahedral 

• Molecular Geometry (MG): Trigonal Pyramidal

What are the structural features of the carbon atoms in an alkane (ex. Methane, ethane)?

• All alkanes have 4 single bonds to either carbon atoms or to hydrogen atoms 

• SATURATED HYDROCARBONS

What are the differences between staggered and eclipsed conformations of an alkane and how can these be represented in two dimensions?

• Staggered conformation: minimize torsional strain; lower energy 

• Eclipsed conformation: maximal torsional strain; high energy- repulsion 

• Represented using (1) Newman projections & (2) Sawhorse projections

What is a Fischer projection and what is the three-dimensional spatial orientation of the various atoms/groups bonded to the central atom(s) in these types of structures?

• Bow tie = same plane 

• Arrows = away

How do the internal angles of a hexagon differ from the internal angles in cyclohexane?

• Internal angles of hexagon = 120 degrees

• Internal angles cyclohexane = 109.5 degrees

How does one translate a Haworth projection of a six atom ring to a chair structure and vice-versa?

• Based on planar structure (HAWORTH)

1. Label carbons

2. Mark A & E position (draw the lines)

3. Then use ups and downs