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Experimental Design and Methods in Chemistry

Yellow Flame

When glass is heated, a yellow flame is observed around the point of heating. What does the yellow flame indicate? Why is it observed when glass is heated?

HPLC Column

An HPLC column of length 15cm and ID of 4.6mm is tightly packed with monodisperse ODS particles of diameter 3:m surface area 300m/g^2 and density 1.2g/mL. Dead volume is 1.2mL. Assuming that the particles are tightly packed and that the void volume is essentially due to the pore volumes of the particles, calculate: 1. the #

GC Problem

Calculate: 1. Corrected retention times for air and 3 alcohols 2. Specific retention volumes for 3 alcohols 3. Distribution constant for 3 alcohols 4. Capacity factor for 3 alcohols 5. The average number of theoretical plates and the average height of a theoretical plate for the column Given: 1. Column length: 1.1m ID

Chemical Separations Problem

The H (height equivalent of a theoretical plate) value for an HPLC column at mobile phase flow rates of 1ml/min, 3ml/min and 4ml/min are 4.1mm, 4.7mm and 5.675mm. Calculate: 1. The van Deemter parameters A, B and C 2. The flow rate at which H is a minimum and the value of H at this flow rate 3. The efficiency N if the length

Preparation of solutions

Hi-1st of all, would you please send back an email address so I may contact someone on the 3rd shift about something that was done on 3rd? Secondly, is there a way to request work to be done by a certain person if they are available? A couple of you last night were just wonderful!!!Olivia Problem: Describe how you would prepar

Chemical separation on a GC instrument

Given: 1. GC instrument 2. polysiloxane column 3. 1mM solution of each of the following compunds in methanol. Compounds divided into 3 separate groups: 1. Carboxylic Acid: a. benzoic acid b. Phthalic acid c. Toluic acid 2. Amino: a. aniline b. 4-aminotoluene c. ortho- pheylenediamine 3. Amino

Method Set-Up for a Chemical Separation

Suggest a buffer and mobile phase composition to get the best separation given: 1. HPLC instrument 2. C18 reverse phase column 3. 1mM solution of each of the following compounds in Methanol 4. Mobile phase is methanol-buffer mixture Compounds are 3 seperate groups: 1. Carboxylic Acids: a. Benzoic acid b

Capacity Factor Problem

Question: Two analytes A and B, have retention times of 13.5 min and 19.5 min, with peak widths of 2 min and 2.8 min for a mobile phase composition of 20% methanol and 80% H2O, on a 15 cm C18 column which has a dead time of 1.5 min. Determine the composition of methanol and H2O at which the capacity factor for A becomes 2. What

Analyte separation problem

The fraction of an analyte in the rth stage of a N stage separation if given by f(N,r)=(N!/r!(N-r)!p^r q^(N-r). Given: distribution ratios of 0.5 and 1.5 Stages 50 and 200 Phase volume ratio 0.3 What is the fraction of analyte in each stage and the stage number for analytes with the given dis

Capillary condensation in nanotubes

Is anyone familiar with a recent report where liquid water has been condensed inside a carbon nanotube and then imaged with an electron microscope at very low pressure (10^-5 torr)? Supposedly the water does not evaporate at this low a pressure. Is this truly possible and why? Does anyone have the reference for this experimen

Solvent-Solvent Extraction

Green Slime, an uncharged organic dye, is present in 600.0mL of water at an unknown concentration. The sample is extracted with 75.00mL of cyclohexane. After the extraction, the absorbance of the cyclohexane phase, measured at 635nm in a 1.00cm cell, is 0.870. The absorbance of a blank (pure cyclohexane) is 0.007. Using Beer's L

Absorption and fluorescence

An aromatic compound, RX, fluoresces at 470 nm (quantum yield = 0.1) after excitation at 340 nm. The molar absorptivity of RX at 340 nm is 1100. How much energy has been lost by non-radiative means or remains with the compound after it fluoresces at 470 nm? How many joules of energy per mole of 340 nm photons is retained by a 10

Absorption and Fluorescence

Question: An aromatic compound, RX, fluoresces at 470 nm (quantum yield = 0.1) after excitation at 340 nm. The molar absorptivity of RX at 340 nm is 1100. How much energy has been lost by non-radiative means or remains with the compound after it fluoresces at 470 nm? How many joules of energy per mole of 340 nm photons is retain

Determine Molar Absorptivity

A red-colored complex PbX4 prepared from Pb with ligand X() shows promise as a means to determine trace levels of lead in the environment. The analyst prepares five standard solutions (A, B, C, D, and E) of PB: 30, 60, 90, 120, and 150 ppm, respectively. 5 ml of each solution is mixed with 5 ml of 0.10 M X. The transmittance of


Methyl Orange is an acid-base indicator. In dilute solution, at a pH greater than 4.4, it is yellow. At pH=3.2, the solution appears red. Draw a structure of the species that is formed at the lower pH of the acid proton that adds to the azo nitrogen atom adjacent to the aromatic ring containing the -SO3 group. Why does the proto

Relative Retention

Retention times for several organic compounds separated on a gas chromographic column are given below: Compound tR(seconds) Air 75 Pentane 190 Heptane 350 2-Pentene 275 a. Calculate the relative retention of 2-Pentene with respect t

Mass Density of Certain Volume

The mass of a certain volume of an unknown liquid at 25 degrees Celsius was determined to be 24 mg. The mass of an equal volume of water at the same temperature was measured as 201 mg. Calculate the density of the unknown liquid at 25 degrees Celsius.

Laboratory Questions

A laboratory has four hoods each of which is 39 inches wide. When the hood door is open to a height of 8 inches and the hoods are operating, the average air velocity through the hood is 170ft/min. a. Evaluate the total ventilation rate for this room assuming that there are no other exhausts. b. The laboratory is designed for

Calculating Absorptivity

I have tried to play with all the numbers in this question, but nothing seems to be working. Nitrite ion, NO-2 is used as a preservative for bacon and other foods. It has been the center of controversy since it is potentially carcinogenic. Here is an abbreviated procedure for the determination: Step 1: 50.0 mL of unk

Key Advanced NMR Definitions

BRAINMASS PROBLEM 10 Please describe the following terms: 1) Larmor Frequency 2) Nuclear Overhauser Effect 3) 180° Pulse 4) Spin Lattice relaxation 5) Free Induction Decay

Understanding Beer's Law

What is Beer's law? Use Beer's law to mathematically determine the unknown concentration values. How do the values derived from Beer's law compare to those derived from the graph?

Identifying different solutions.

If I had 5 solutions that are not labeled (the solutions are ethanoic acid, calcium hydroxide, potassium bromide, sodium chloride and nitric acid) is there a way of identifying which one is which without using an indicator?