Calibration of a glass electrode gave a reading of 139.7 mV with saturated potassium hydrogen tartrate buffer standard (pH = 3.557) and a reading of -92.2 mV with 0.08 m HEPES, 0.08 m NaHEPES, 0.08 m NaCl buffer standard (pH = 7.454), both measured at 30°C.

(a) What is the observed slope (mV/pH unit) of the calibration curve?

(b) What is the theoretical slope at 30°C?

(c) What is β, the electromotive efficiency to three significant figures?? Open the hint panel below for the definition of electromotive efficiency.

(d) What is the pH of an unknown that gives a reading of 46.9 mV with this electrode at 30°C?

Write the balanced equation for the combustion of aqueous citric acid. Determine the standard molar enthalpy of aqueous citric acid. citric acid can constitute 8% of the dry weight of limes if a typical lime contains 30 ml of juice how much energy is released when one lime is combusted?

A compound of molecular formula C7H13Br is a tertiary bromide, is optically inactive, and has one primary carbon atom. C7H13Br is inert to catalytic hydrogenation. C7H13Br is reacted with another unknown compound. Thin-layer chromatography of the product mixture shows that two products are formed. GC analysis shows that the two products are formed in unequal amounts. Upon isolation from each other via distillation, both isolated products are optically inactive. Both products de-colorize molecular bromine.

Answer questions a-c below.

a. Based on the information provided, is the reaction between the tertiary bromide and the unknown compound a: 1. substitution, or 2. elimination reaction? ________

b. Will the organic starting material give a positive (P) or negative (N) result for the silver nitrate in alcohol test? ________

c. Propose a structure for C7H13Br. Name the structure.

1. Write the balanced equation (not the mechanism) for the protonation of nitric acid by sulfuric acid, represented as an equilibrium expression.

2. Write the equilibrium constant expression for the reaction shown in question 1 above.

3. Consider the pKa values shown below:

H2SO4: -3

HSO4!: +2

HNO3: -1.3

H2NO3+: -13

Based on these pKa values, determine the equilibrium constant for the reaction that you wrote down for question 1.

4. The proton NMR spectrum of chlorobenzene was examined by Hiyamizu and coworkers in 1968. Their analysis revealed the following chemical shifts. The hydrogens ortho to the chlorine are at 7.28 ppm. The hydrogens meta to the chlorine are at 7.23 ppm. The hydrogen para to the chlorine is at 7.16 ppm.

A) Use arrow formalisms to draw resonance structures of chlorobenzene using the chlorine as an electron donor.

B) One might expect that the positions that have negative charges (and hence excess electron density) in the resonance structures would be the most upfield, but this is not the case. Explain why, and explain why the chemical shifts appear where they do relative to each other.

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?