CHEM 2001 Final AJJ

The mass balance equation for a 0.10 M HO2CCO2H solution is which of the following? Remember that HO2CCO2H(aq) is in equilibrium with HO2CCO2- and -O2CCO2-

0.10 M = [HO2CCO2H] + [HO2CCO2-] + [-O2CCO2-]

The buffering range for a weak acid is when: pH = pKa ± _____.

1

How many liters are in a microliter (µL)?

1x10⁻⁶L = 1µL

How many liters are in a nanoliter (nL)?

1x10⁻⁹L = 1nL

How many significant figures does 0.0043g have?

2

How many significant figures does 59.0 km have?

3

How many significant figures does 1.003 L have?

4

How many significant figures does 95.00km have?

4

How many significant figures does 19.830g have?

5

How many significant figures does 12.9830g have?

6

Which statement below is INCORRECT for the increased solubility of a sparingly soluble salt, AgCl, in an inert salt solution, NaNO3? A) The ionic atmosphere increases the attraction between silver cations and chloride anions, increasing solubility by creating more AgCl(aq) in solution. B) The ionic strength around the chloride anions becomes increasingly positive as the sodium cations are attracted to the chloride anions. C) The ionic atmosphere around the silver cations becomes increasingly negative as the nitrate anions are attracted to the silver cations. D) Ions continually diffuse into and out of the ionic atmosphere. E) The negative ionic atmosphere around silver cations results in an overall positive charge less than the positive charge of the silver cations.

A) The ionic atmosphere increases the attraction between silver cations and chloride anions, increasing solubility by creating more AgCl(aq) solution

The end point for the Fajan's titration is indicated by: A) adsorption of a colored indicator on the precipitate at the end point B) reduction of a colored indicator at the endpoint C) deprotonation of a colored acid-base indicator at the end point D) formation of a soluble, colored complex at the end point E) protonation of a soluble, colored complex at the end point

A) adsorption of a colored indicator on the precipitate at the end point.

A student prepares a solution using a 1L volumetric flask. When he finishes, the meniscus is above the calibration mark on the flask neck. The concentration of the solution is: A) less than calculated B) greater than calculated C) unchanged D) irrelevant E) impossible to predict

A) less than calculated

The key step in titration calculations is to relate: A) moles titrant to moles analyte B) volume titrant to volume analyte C) grams titrant to grams analyte D) conductivity titrant to conductivity analyte E) reduction titrant to oxidation analyte

A) moles titrant to moles analyte

Argentometric titrations are titrations using: A) Au⁺ B) Ag⁺ C) Ar⁺ D) Al³⁺ E) As³⁻

B) Ag⁺

Which statement is FALSE regarding the titration of a weak acid with a strong base? A) At the equivalence point, the pH is due to the hydrolysis of water by the conjugate base, A-. B) Past the equivalence point the pH is due to excess conjugate base, A-. C) Before strong base is added, the pH is due to the ionization of the weak acid, HA. D) The pH at the equivalence point is basic.

B) Past the equivalence point the pH is due to excess conjugate base, A-.

The buffer needed for capillary elctrophoresis experiment must have a pH of 10.0. Which weak acid is the best choice for the buffer? Assume µ=0. A) ammonium chloride --- pKa=9.24 B) disodium phosphate --- pKa=12.38 C) 3-(Cyclohexylamino)propanesulfonic acid --- pKa=10.40 D) sodium dihydrogen borate --- pKa=12.74 E) cyclohexylaminoethanesulfonic acid --- pKa=9.39

C) 3-(Cyclohexylamino)propanesulfonic acid --- pKa=10.40

Which is NOT a property of buffers? A) Buffers resist changes in pH when acids or bases are added or when dilution occurs. B) Buffers are a mixture of weak acid and conjugate base. C) The pH of a buffer is independent of ionic strength D) The pH of a buffer is dependent on temperature. E) Buffers are a mixture of weak bases and conjugate acid.

C) The pH of a buffer is independent of ionic strength.

Which of the following terms is INCORRECTLY defined? A) titration error: the difference between the end point and the equivalence point B) direct titration: titrant is added to analyte until reaction is complete C) equivalence point: volume of titrant added in excess of the end point to change a physical property of the analyte solution D) blank titration: titration performed without analyte to calculate titration error E) standardization: titration of known amount of analyte to determine the concentration of titrant

C) equivalence point: volume of titrant added in excess of the end point to change a physical propery of the analyte solution

The end point for the Volhard titration is indicated by: A) adsorption of a colored indicator on the precipitate at the end point B) reduction of a colored indicator at the endpoint C) deprotonation of a colored acid-base indicator at the end point D) formation of a soluble, colored complex at the end point E) protonation of a soluble, colored complex at the end point

D) formation of a soluble, colored complex at the end point

All of the following are TRUE for activities and activity coefficients, except: A) activity for a chemical species is the product of concentration and activity coefficient B) the activity coefficient corrects for non-ideal behavior due to ionic strength C) the activity coefficient for neutral molecules is approximately unity when the ionic strength is less than 0.1 M D) for ions, the activity coefficient approaches unity as the ionic strength approaches 0 E) as ionic strength increases, the value of the activity coefficient increases

E) as ionic strength increases, the value of the activity coefficient increases

The strongest acid that can exist in water is _______.

H₃O⁺

A data point may be excluded when: (all that apply) I. G_calculated is greater than G_table II. G_calculated is less than G_table III. your TA or supervisor says to disregard the datum IV. the datum is the result of a faulty procedure

I. G_calculated is greater than G_table and IV. the datum is the result of a faulty procedure

Which of the following is not a way to demonstrate the accuracy of a method? I. Determine the limit of detection for a method. II. Analysis of a certified reference material in a matrix similar to the sample. III. Compare the results between two or more different analytical methods. IV. Analyze a blank sample with a known amount of analyte in the same matrix as the sample.

I. determine the limit of detection for the method.

For the reaction HCN(aq) + H₂O(l) ↔ CN⁻(aq) + H₃O⁺(aq), all of the following will shift the equilibrium toward the products, except: I. adding HCN II. adding H₂O III. removing CN⁻ IV. removing H₃O⁺

II. adding H₂O

Which is NOT a general step in the analytical process? I. Sample Preparation II. Selecting analytical procedures III. Make policy IV. Reporting and interpretation V. Analysis

III. Make policy

_________ are calibrated to deliver one fixed volume and are ______ than ___________. I. Measuring pipets; more accurate; transfer pipets II. Transfer pipets; less accurate; measuring pipets III. Measuring pipets; more precise; transfer pipets IV. Transfer pipets; more accurate; measuring pipets V. None of these answers are correct

IV. Transfer pipets; more accurate; measuring pipets

Which term is INCORRECTLY defined? I. linear range: the range over which the response of an analytical method is proportional to analyte concentration II. corrected absorbance: the average absorbance of the blanks is subtracted from each measured absorbance III. blank solution: solution containing all reagents and solvents used in the analysis to which no analyte is deliberately added IV. standard solutions: solutions for which the standard deviation is known V. dynamic range: concentration range over which there is a measurable response to analyte, though the response is not linear

IV. standard solutions: solutions for which the standard deviation is known

________ is the difference between the observed end point (color change) and the true equivalence point.

Indicator error

______________ is a measure of the total concentration of ions in solution.

Ionic strength

The slope of the linear portion of a Gran plot is _______ and the x-intercept is _____

Ka and Ve

The strongest base that can exist in water is ______.

OH⁻

True or false. For strong base solutions with concentrations ≤10⁻⁹ M, the pH is 7.

True

A buffer is prepared from NaH2PO4 and Na2HPO4 in water. The charge balance balance equation for the buffer is which of the following? Assume PO4^3- and H3PO4 are negligible.

[Na+] + [H+] = [H2PO4-] + 2[HPO4^2-] + [OH-]

A(n) _________ is itself an acid or base whose various protonated species have different colors.

acid-base indicator

The pH of a solution is 4.65. The solution is ________ and the hydroxide concentration is __________ than the hydronium concentration.

acidic, less

To correct for the effect of ionic strength on chemical reactions, concentrations are replaced by ________ in equilibrium expressions.

activities

To correct for the effect of ionic strength on chemical reactions, concentrations are replaced by ___________ in equilibrium expressions.

activities

A molecule that can act as a base or an acid is called _____________.

amphiprotic

__________ is the substance being measured during chemical analysis.

analyte

The Gaussian distribution is characterized by the ________ and the _________.

average (mean), standard deviation

The pH of a solution is 9.65. The solution is ________ and the hydroxide concentration is _________ than the hydronium concentration.

basic, greater

A(n) ____________ curve is a plot of detector response as a function of analyte concentration. The curve is constructed using ____________ solutions containing known concentrations of the analyte of interest.

calibration, standard

For a solution of a sparingly soluble salt, AgCl, in an inert salt solution, NaNO₃, the ionic atmosphere (decreases or increases) the attraction between silver cations and chloride anions, increasing solubility by creating more Ag⁺ and Cl⁻ in solution.

decreases

The activity coefficient (increases/decreases) as the charge on a particular ion increases.

decreases

The activity coefficient (increases/decreases) as the ionic strength of a solution increases. Note: for ionic strengths < 0.1 M

decreases

For a weak acid, the ion size of HA ____________ and the ion size of A- _____________ with increased pH.

decreases, increases

If a base stronger than OH⁻ is dissolved in water, it ________ H₂O to make ______.

deprotonates, OH⁻

______ range is the concentration range over which there is measurable instrument response.

dynamic

For a weak base, the maximum buffer capacity is when [B] (< or = or >) [BH⁺]?

equal

The titration error is the difference between the ____________ and the _____________.

equivalence point and end point

True or false. For a triprotic acid, Ka₁(Kb₂)=Kw.

false

When K>1, the equilibrium reaction will proceed in the forward or reverse direction.

forward

A favorable enthalpy change occurs when ∆H is negative. Does a systen absorb heat or give off heat when ∆H is negative?

give off heat

A ________ is a graph of Vb x 10^-pH versus Vb.

gran plot

A __________ uses data from before the end point to located the end point.

gran plot

For a reaction with a ∆H°= -74.85 kJ and a ∆S°= -130.4 J/K, ∆G° is -35.97 kJ/mol and the equilibrium constant is less than or greater than 1.

greater than

__________ is a set of principles intended to help sustain a habitable planet.

green chemistry

A(n) ___________ sample is a sample where the chemical composition differs from place to place.

heterogeneous

A(n) ________ sample is a sample where the chemical composition is the same from place to place.

homogeneous

The activity coefficient (increases/decreases) as the "ion size" increases.

increases

A(n) __________ is a compound with a physical property that changes abruptly near the equivalence point.

indicator

___________ occurs when a species other than analyte increases or decreases the analytical signal and makes it appear that the concentration is greater or less than the real concentration.

interference

A(n) ____________ is a known amount of compound, different from the analyte, that is added to the unknown.

internal standard

_____________ is a measure of the total concentration of ions in solution.

ionic strength

What is the SI unit for mass?

kg

The ________ fulfills the critical function of reporting what a researcher has done and what they observed, and allows another researcher to repeat their work.

lab notebook

In strong base, the red phenolphthalein __________.

loses its color

The _______________ is everything in the sample, except analyte.

matrix

A _________ is a sample containing all components except analyte, and it is taken through all the steps of the analytical procedure.

method blank

For a solution of a sparingly soluble salt, AgCl, in an inert salt solution, NaNO₃, the ionic atmosphere around the silver cations becomes increasingly (positive or negative) as the nitrate anions are attracted to the silver cations.

negative

In strong acid, the colorless form of phenolphthalein turns ________.

orange-red

If an acid stronger than H₃O⁺ is dissolved in water, it ________ H₂O to make _______.

protonates, H₃O⁺

__________ chemical analysis is the determination of what is present in the sample.

qualitative

_________ chemical analysis is the measurement of how much of a chemical substance is present.

quantitative

When K<1, the equilibrium reaction will proceed in the (forward or reverse) direction.

reverse

Choose an indicator whose transition range overlaps the ________ part of the titration curve.

steepest

_______ error is consistent error that can be detected and corrected.

systematic

For strong acid solutions with a concentration between 10⁻⁶ and 10⁻⁸ M, the pH is determined using ______________.

systematic treatment

True or false. For a triprotic acid, K_a₁(K_b₃)=K_w.

true

True or false. pH = -log[H+] when ionic strength = 0

true

The conjugate acid of a strong base is (weak or strong)?

weak

The conjugate base of a weak acid is (weak or strong)?

weak

Amino acids are called ______________ because they can have a positive and negative charge at the same time.

zwitterions