you are instructed to add enough triethylene glycol (TEG) to make the solution 0.6 M in meso-stilbene dibromide. Suppose you 200 mg of meso-stilbene dibromide. What volume of TEG would be required?

At 1 atm, how much energy is required to heat 35.0 g of H2O(s) at –20.0 °C to H2O(g) at 173.0 °C?

Question to answer after EXPERIMENT OF SPECTROPHOTOMETRIC DETERMINATION OF TRACE Fe

Principles The purpose of this experiment is to determine the concentration of iron present as a trace constituent (ppm) in an aqueous sample by a spectrophotometric method. One of the most sensitive methods for the determination of iron involves the formation of the orange-red iron (II) orthophenanthroline complex. This complex has an absorption maximum at 508 nm, is stable over a long period of time, and follows Beer's Law quite faithfully.

The chemistry involved is straightforward. Hydroxylamine hydrochloride is used to reduce all Fe3+ present to Fe2+. Since orthophenanthroline (abbreviated as phen) is a weak base and an acid medium must be used in order to prevent precipitation of the iron as Fe(OH)2, the principal complexing species is the phenanthrolium ion (phenH+ ). The complex formation reaction:

Fe2+ + 3phenH+  Fe(phen)3 2+ + 3H+

has an equilibrium constant of 2.5 x 106 , so complex formation may be considered quantitative. Although pH control is not essential, too high of an H+ concentration (pH<2) can inhibit formation of the complex, while too high of a pH can cause the loss of iron by precipitation. Thus, the solution is buffered to be to about a pH of 3.5.

Since the system obeys Beer's Law, above, a plot of absorbance at 508 nm versus iron concentration yields a straight line. Thus, one can prepare a set of standard solutions of known concentrations, establish a straight line, and prepare the unknown solution in exactly the same way. If the absorbance of the unknown solution is measured, the unknown concentration may be determined from the analytical curve generated with the standard solutions.

Questions:

1. The ferrous ammonium sulfate used as a standard in this experiment is not of primary standard quality, yet you were not instructed to standardize this reagent 81 before use. Why is it not necessary to standardize this analytical reagent before use in this experiment? Explain.

2. Describe two reasons why deviations to Beer's Law (i.e. nonlinearity) can occur.

3. The sensitivity of spectrophotometric methods can greatly exceed sensitivities attainable with classical wet chemical methods. How do the Fe concentrations analyzed in this spectrophotometric experiment compare with the Fe concentrations used in the redox titration experiment? Be quantitative!

Chloride ions, Cl- (aq) can be electrolyzed in water to Cl2 (aq). If 198.3 mA of current flows through a platinum electrode immersed in a 0.200 M Br solution for 4.44 hr, how many grams of cl2 will be produced? MM Cl2= 35.45 g.


I got 1.15 grams but im not sure if i am doing this right

When performing a REAGENT BLANK in chemistry, do you add or subtract the volume of the blank determination from the volume of titrant to get the corrected volume of titrant used? In this particular experiment we are determining Ca2+ and Mg2+ in natural water samples. And, do you always add or subtract the blank reagent or does it change with reactions? Probably simple questions but they have me completely stumped. Thanks!

What precipitate forms when aqueous soulutions of Potassium Chloride, Sodium Sulfide, Iron(II) Nitrate are simultaneously mixed? Show the molecular and net ionic equation for the reaction.

Draw Lewis dot structure (CH3)4 NCL A SALT

Which of the following species represents an exception to the octet rule?

Calculate the pH of a solution prepared by mixing 300mL of 0.25M sodium hydrogen ascorbate and 150mL of 0.2M HCl plus water to a final volume of 1 liter. The Ka of ascorbic acid is 5.0 x 10^-5

Calculate the standard cell potential for each of the following electrochemical cells.

Part A

Ni2+(aq)+Mg(s)→Ni(s)+Mg2+(aq)

Express your answer using two decimal places.

E∘cell = _____  V

Part B

2H+(aq)+Fe(s)→H2(g)+Fe2+(aq)

Express your answer using two decimal places

E∘cell =_______ V

Part C

2NO−3(aq)+8H+(aq)+3Cu(s)→2NO(g)+4H2O(l)+3Cu2+(aq)

Express your answer using two decimal places.

E∘cell = ________V

b. A graduated cylinder contains 45.0mL of water. When a metal rod is submerged into the water, the liquid level rises to 50.0mL. What is the volume of the metal rod in cm³? If the metal rod weighed 55.0g, what is the density of the metal rod in g/mL and g/cm³?

c. What is the mass of a substance that has a density of 8.0g/cm³ and a volume of 125cm³?

d. Determine the volume of a substance that has a mass of 750.0g and a density of 2.5g/mL.

e. A student finds that a piece of metal has a mass of 12.54g. When the metal is placed inside a flask that has a volume of 25.00mL, the student finds that 20.54g of water is required to finish filling the flask with the metal in it. If the density of water is 0.9970g/cm³, what is the density of the metal?

The pKb values for the dibasic base B are pKb1 = 2.10 and pKb2 = 7.37. Calculate the pH at each of the following points in the titration of 50.0 mL of a 0.55 M B(aq) with 0.55 M HCl(aq).

(a) before addition of any HCl

(b) after addition of 25.0 mL of HCl

(c) after addition of 50.0 mL of HCl

(d) after addition of 75.0 mL of HCl

(e) after addition of 100.0 mL of HCl

You have 625 mL of an 0.23 M acetic acid solution. What volume (V) of 2.10 M NaOH solution must you add in order to prepare an acetate buffer of pH = 5.03? (The pKa of acetic acid is 4.76.)

A 0.5206 g solid sample containing a mixture of LaCl3 (molar mass = 245.26 g/mol) and Ce(NO3)3 (molar mass = 326.13 g/mol) was dissolved in water. The solution was titrated with KIO3, producing the precipitates La(IO3)3(s) and Ce(IO3)3(s). For the complete titration of both La3 and Ce3 , 43.38 mL of 0.1236 M KIO3 was required. Calculate the mass fraction of La and Ce in the sample.​

Fill in the blanks

1. the ____ atoms of the ____ groups and the hydrogen atoms attached to the ____ atoms form ____.

(answer choices; nitrogen, carbon, a-helices or b-pleated sheets, carbonyl, globular of firbrous structures, oxygen, amino, random coil, thiol)

2. In the a helix, hydrogen bonds form between the ____ oxygen atom and the ____ hydrogen atom of a peptide bond in _____. In the B-pleasted sheet, hydrogen bonds form between the ____ oxygen atom and the ____ hydrogen atom of a peptide bond in ____.

(answer choices; parallell sections of a long polypeptide chain, the next amino acid unit, carboxyl, the next turn of the helical chain, thiol, amino, carbonyl)