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Which of these analytical techniques is most suitable for quantifying the concentration of methanol in a biological liquid?
|
Gas chromatography with flame ionization detection.
|
High performance liquid chromatography (HPLC) with UV-visible detection.
|
Turbidimetric immunoassay (immunoturbidimetry)
|
Chemistry
|
MALDI-TOF.
| 134 | 2 |
f36ee68d-a934-411e-b285-6d3cdfe48f20
|
2021
|
What is the pH of the solution that results from adding 20 mL of 0.10 M NaOH to 40 mL of 0.10 M formic acid (H-COOH)? Given: pKa (H-COOH) = 3.8.
|
pH=3.8.
|
pH=2.8.
|
pH=7.0.
|
Chemistry
|
pH=4.8.
| 135 | 2 |
1876ce5e-a448-412c-a152-94494839cb61
|
2021
|
In the technique of capillary zone electrophoresis, the electroosmotic flow rate:
|
Increases as the pH of the separation buffer decreases.
|
Increases as the pH of the separation buffer increases.
|
Increases as the ionic strength of the separation buffer increases.
|
Chemistry
|
It is independent of the viscosity of the separation buffer.
| 136 | 1 |
a4f7201e-6074-4750-98ba-be51cbbb49ec
|
2021
|
HA and A- represent a conjugate acid-base pair, and ๐๐ฒ๐(๐๐) = ๐.7. What will be the pH of an aqueous solution in which the concentration of A- is 10 times greater than the concentration of HA?
|
4.7.
|
5.8.
|
6.7.
|
Chemistry
|
5.7.
| 137 | 4 |
6032a0ac-ab88-45da-a1f2-15d4cadc6afa
|
2021
|
The flame used in a flame ionization detector (known by its acronym in English FID) is composed of:
|
Nitrogen + Helium.
|
Helium + Hydrogen.
|
Air + Helium.
|
Chemistry
|
Hydrogen + Air.
| 138 | 3 |
763d7fa4-d3f1-4682-933a-2d51b21b6a7a
|
2021
|
The thermal conductivity detector used in gas chromatography technique is characterized by:
|
It is a universal detector that serves to detect any compound, organic or inorganic, that comes out of the column.
|
It is a destructive detector.
|
It is a detector that measures the thermal conductivity of the compounds that are separated.
|
Chemistry
|
It is a high sensitivity detector.
| 139 | 2 |
0de13b83-aa1e-41ef-bcdc-82b01cc36dbd
|
2021
|
In column liquid chromatography, we refer to "dead time" as:
|
Time that the solute spends outside of the column packing.
|
Time that the solute spends "absorbed" within the column packing.
|
Time it takes for a non-retained substance to elute and reach the detector.
|
Chemistry
|
Time it takes for a strongly retained substance to elute and reach the detector.
| 140 | 4 |
70fefe75-f14f-43dd-ba1b-b5d58533a9e9
|
2021
|
In which of the following molecules will electronic transitions occur in the visible region of the spectrum?
|
Iron pentacarbonyl.
|
Sodium chloride.
|
Titanium dioxide.
|
Chemistry
|
Chloroform.
| 141 | 2 |
25a22812-af18-4fbe-a501-6f016d526f7b
|
2021
|
In which region of the electromagnetic spectrum is a wavelength of 6.0 ร 10โ3 cm found?
|
Ultraviolet.
|
Infrared.
|
Microwave.
|
Chemistry
|
Visible.
| 143 | 1 |
6dc7d251-bfaf-4841-b796-9153928ec25b
|
2021
|
In a second-order chemical reaction, the half-life (t1/2) is:
|
Inversely proportional to the initial concentration of the reactant.
|
Proportional to the initial concentration of the reactant.
|
Inversely proportional to the square of the initial concentration of the reactant.
|
Chemistry
|
Independent of the initial concentration of the reactant.
| 144 | 2 |
206349f5-2d39-44d7-902b-79be1505b5f9
|
2021
|
The wave function ๐(๐, ๐, ๐) represents an orbital:
|
3p.
|
3S.
|
It does not represent any orbital.
|
Chemistry
|
3d.
| 145 | 4 |
c1bcb157-bec4-423f-b7ee-50c8ca1fb440
|
2021
|
In the case of gases that are sparingly soluble in liquids, the concentration of dissolved gas is generally low enough for the solution to be approximately ideal and the following holds true:
|
Henry's Law.
|
Raoult's Law.
|
Dalton's law.
|
Chemistry
|
Faraday's Law.
| 146 | 2 |
27be2320-8b8f-47b0-9cdd-44aa14e8a259
|
2021
|
The property that characterizes the resistance of a liquid to flow is its viscosity, ฮท, in N โง s โง mโ2. Gases are much less viscous than liquids. The relationship between the viscosities of water and benzene, both liquids, at 20ยบC and atmospheric pressure is:
|
ฮท(water) > ฮท(benzene), due to the existence of hydrogen bonds.
|
ฮท(water) = ฮท(benzene), they are liquids at the given pressure and temperature.
|
it cannot be known with the available information.
|
Chemistry
|
ฮท(water) < ฮท(benzene), due to the existence of short-range forces.
| 147 | 2 |
1688bc29-4011-4879-9f39-67237cc3a452
|
2021
|
Capillary descent and ascent are surface phenomena that, for the same liquid, fundamentally depend on:
|
On the viscosity of the liquid.
|
Intermolecular forces.
|
Of the external pressure.
|
Chemistry
|
From the radius of the capillary and the surface tension of the liquid.
| 148 | 3 |
d285efcf-b7cd-472e-808b-5f4d9f031246
|
2021
|
Which of the following transitions between quantum energy levels of the hydrogen atom produces the third line of the second series of the spectrum of said atom?:
|
n1 = 3 n2 = 2.
|
n1 = 5 n2 = 2.
|
n1 = 4 n2 = 2.
|
Chemistry
|
n1 = 4 n2 = 1.
| 149 | 1 |
840a5541-6f34-4ba4-8fd0-39234f156efe
|
2021
|
When writing the molecular electronic configuration of NO, we deduce:
|
The bond order is 5/2.
|
The bond order is 7/2.
|
The bond order is 4.
|
Chemistry
|
It is diamagnetic.
| 150 | 2 |
f440d0f9-39e2-4eb1-b8ee-a67228161e4f
|
2021
|
According to the Debye-Hรผckel limiting law, what condition does the mean ionic activity coefficient, (๐ธ ยฑ), meet?
|
It decreases with the ionic intensity, I of the solution.
|
Increases with the ionic intensity, I of the solution.
|
It is independent of the ion concentration in the medium.
|
Chemistry
|
It is independent of the ionic intensity.
| 151 | 2 |
c2bfa3e9-e190-4a45-8a07-f58100109a53
|
2021
|
What is the main utility of the Valence Shell Electron Pair Repulsion Theory?
|
Provide a qualitative theoretical explanation of molecular structures.
|
Calculate the space occupied by a lone pair of an atom.
|
Explain the formation of chemical bonds through the outer electrons of atoms.
|
Chemistry
|
Justify that the geometry of the carbons in saturated hydrocarbons is planar triangular.
| 152 | 2 |
d56f658e-1a74-4a67-8b62-7c758bd2f70f
|
2021
|
The average distance traveled in a given direction and in a specified time by a molecule experiencing random diffusion is 3 cm in 1 minute in a gas at ambient P and T. Why does a student who is located at the end of a 10 m long classroom smell a citrus scent that spreads from the teacher's stage in a couple of minutes?
|
The student should instantly smell the citrus aroma.
|
The molecule causing the citrus aroma in the classroom moves by diffusion and migration.
|
Under uncontrolled conditions (variations in density and T), very effective convection currents exist.
|
Chemistry
|
The student is confused, he cannot smell the citrus aroma.
| 153 | 4 |
66ea478d-b2e8-45b0-bc95-95b15b515678
|
2021
|
A helium atom, with two electrons, in its excited state, can be in a singlet or triplet state. What is the difference between both situations?:
|
In the singlet state, the spin moment is zero and in the triplet, the spin moment is NOT zero.
|
In the singlet state, the spin moment is NOT zero and in the triplet state, the spin moment is zero.
|
The triplet state cannot exist for the helium atom.
|
Chemistry
|
The singlet state cannot exist for the helium atom.
| 154 | 2 |
c8c73df8-673c-4d02-9e7b-a1165d63d88c
|
2021
|
The relationship between ฮrG and ฮrG0 is formulated as a relationship between Q, the quotient of activities, and K0, the equilibrium constant, in the form: ๐ซr๐ = ๐ซr๐ฎ๐ + ๐๐ ๐๐ง ๐ = ๐๐ ๐๐ง ๐ธ ๐ฒ๐. Decide which statement is correct:
|
ฮrG = 0 โ Q = 1.
|
ฮrG = 0 โ K0 = 1.
|
ฮrG < 0 โ Q < K0.
|
Chemistry
|
ฮrG > 0 โ K0 > Q.
| 155 | 4 |
19f6d14b-0e74-4466-aaf7-c33fdc8d143b
|
2021
|
When a metal is exposed to electromagnetic radiation, the emission of electrons may occur. Indicate, from the following statements, the one you consider correct:
|
All metals have the same work function.
|
The representation of the kinetic energy of the expelled electrons against the frequency of the incident radiation has a slope that is equal to the value of the work function.
|
The representation of the kinetic energy of the ejected electrons as a function of the frequency of the incident radiation is a straight line.
|
Chemistry
|
The kinetic energy of the ejected electrons increases when the intensity of the incident radiation increases.
| 156 | 4 |
7163e8e6-6c67-4cd4-8f45-925e6f828514
|
2021
|
If instead of deionized water, an aqueous solution of KNO3 was used to prepare a saturated solution of AgCl, then:
|
The solubility product of AgCl would not change.
|
The solubility of AgCl would decrease.
|
The ionic strength of the solution would not change.
|
Chemistry
|
The mean ionic activity coefficient of AgCl would increase.
| 157 | 2 |
99711bfd-d559-4e29-9a02-f853ea4e5f5f
|
2021
|
In a dilute solution of a solute B in a solvent A, the cryoscopic depression:
|
It is inversely proportional to the melting temperature of the solvent and the molality of the solution.
|
It is directly proportional to the enthalpy of fusion.
|
It is inversely proportional to the melting temperature of the solvent.
|
Chemistry
|
It is directly proportional to the molality of the solution.
| 158 | 3 |
a438ba2d-c26b-4d87-95c5-b8a560e66381
|
2021
|
For an ideal solution of two components at constant temperature and pressure, it holds that:
|
The enthalpy of mixing is less than zero.
|
The Gibbs free energy of mixing is less than zero.
|
The volume of the mixture is less than zero.
|
Chemistry
|
The entropy of mixing is less than zero.
| 159 | 1 |
22c2a0e5-5e63-4cae-bccf-9ad725322e1c
|
2021
|
What does Henry's law establish?
|
The solubility of a gas increases as the pressure of said gas increases.
|
A supersaturated solution is unstable.
|
A concentrated solution reduces the freezing point of a solution.
|
Chemistry
|
The solubility of a gas decreases as the pressure of that gas increases.
| 160 | 2 |
97e6c1fe-c88a-45b7-8bfb-ba205b81d614
|
2021
|
How is the composition of vapor in equilibrium with a liquid solution of two volatile components determined?
|
It will be equal to the vapor pressure of component i in the solution divided by the vapor pressure of the pure component.
|
It is the same as the composition of the solution itself.
|
It will be equal to the total pressure divided by the vapor pressure of the pure component.
|
Chemistry
|
It will be equal to the partial pressure of component i divided by the total pressure.
| 161 | 3 |
2b623e6f-eee0-4f99-8a81-79668603fa24
|
2021
|
What is the characteristic of a mixture of two components that has reached the eutectic composition?
|
It melts at a lower temperature than any other mixture of any composition.
|
It melts at a higher temperature than any other mixture of any composition.
|
The mixture cannot melt at that composition.
|
Chemistry
|
Melts at the same temperature regardless of the composition.
| 162 | 2 |
b74a4990-aa11-40b1-af7b-d7a44a5e8748
|
2021
|
Are all molecules active for infrared spectroscopy?
|
No, only symmetric polyatomic molecules are active.
|
Yes, any molecule presents vibrational levels between which transitions can occur when it is illuminated by infrared light.
|
No, only the molecules capable of generating a change in their electric dipole moment during the vibrational transition are active.
|
Chemistry
|
No, only molecules that include chromophoric groups in their structure are active.
| 163 | 4 |
45de8026-b052-4061-b238-3e3fad4e71cc
|
2021
|
From the fact of the spontaneous adsorption of acetic acid onto activated charcoal at room temperature, it can be deduced that:
|
The enthalpy of adsorption is equal to zero.
|
The enthalpy of adsorption is greater than zero.
|
The adsorption entropy is greater than zero.
|
Chemistry
|
The enthalpy of adsorption is less than zero.
| 164 | 3 |
e4098bc9-3cbe-4d05-bbec-e555abeb60e3
|
2021
|
What does the triple point of a pure substance indicate?
|
The highest pressure and temperature at which the liquid phase of a substance can exist.
|
The highest pressure at which the liquid phase of a substance can exist.
|
The lowest pressure at which the liquid phase of a substance can exist.
|
Chemistry
|
The lowest temperature at which the vapor phase of a substance can exist.
| 165 | 4 |
34d872b8-71f3-440a-be01-ccfd2d501ebc
|
2021
|
Which parameter/s of the rate law of a chemical reaction can be determined by the initial rates method:
|
The rate constant.
|
The speed of the reaction.
|
The activation energy.
|
Chemistry
|
Partial orders of reaction.
| 166 | 3 |
956481ca-94a9-42d3-94de-a73d42a5dc06
|
2021
|
Which statement is correct in relation to nuclear magnetic resonance?
|
The nuclear magnetic resonance spectrum can distinguish between non-equivalent nuclei at different sites of a molecule.
|
The nuclear magnetic moment strongly interacts with an external magnetic field.
|
The main limitation of NMR in medicine is the partial destruction of the tissues whose image is to be obtained.
|
Chemistry
|
The multiplet splitting of peaks is due solely to the coupling with nearby nuclei.
| 167 | 2 |
cb8550e9-5285-4279-8309-c1e5a43d3887
|
2021
|
Knowing that the normal reduction potentials Eยบ of the following systems are (Zn2+/Zn) = -0.76 V and (Pb2+/Pb) = -0.13 V, indicate the correct statement regarding the galvanic cell constructed with these two electrodes:
|
The negative pole will be lead.
|
The positive pole will be zinc.
|
The Pb2+ acts as an oxidizing agent.
|
Chemistry
|
The reaction that will take place in the battery will be: Zn2+ + Pb โ Zn +Pb2+, since zinc is the reducing agent.
| 168 | 4 |
f0e0a6a1-1afc-413c-91a2-c3a50eb0d287
|
2021
|
Which of the following sets of quantum numbers is possible for an electron located in the 4d orbital?:
|
n = 4 l = 2 ml = +1 s = +1/2.
|
n = 4 l = 4 ml = -3 s = +1/2.
|
n = 4 l = 3 ml = -2 s = +1/2.
|
Chemistry
|
n = 4 l = 1 ml = -2 s = -1/2.
| 169 | 2 |
9b3b8e08-70d6-4041-92d2-1ae719a11307
|
2021
|
The independent intensive variables used to describe a system composed of solid sucrose in equilibrium with an aqueous sucrose solution may be:
|
Pressure, temperature, and volume.
|
Pressure, temperature and molar fraction of sucrose in the aqueous phase.
|
Pressure and temperature.
|
Chemistry
|
Pressure and volume.
| 170 | 4 |
7473c261-6973-4114-a6be-46d43bea31f3
|
2021
|
What does an excess function indicate?
|
The difference between the thermodynamic function of a pure component and the function for the pure component with ideal behavior.
|
The difference between the thermodynamic function observed in the mixture and the function for an ideal solution.
|
The difference between the thermodynamic function of pure components and the function for an ideal solution.
|
Chemistry
|
The difference between the observed thermodynamic function of the mixture and the function for the pure components.
| 171 | 1 |
712aa61c-908f-4bcd-9e8c-fe81966bde00
|
2021
|
Considering that for the reaction: H2(g) + S(s) โ H2S(g), โHยฐ < 0, โSยฐ > 0 and |โHยฐ| > |โSยฐ|, mark what is correct:
|
The reaction is spontaneous at any temperature.
|
The reaction is only spontaneous at low temperatures.
|
The reaction is not spontaneous in any case.
|
Chemistry
|
The reaction is spontaneous only at high temperatures.
| 172 | 2 |
6badb663-f97b-491c-bcda-5fa2737f416b
|
2021
|
How does molar conductivity vary with concentration in a solution where the solute is an electrolyte?
|
If the electrolyte is strong, the molar conductivity is much higher at high concentrations, when the number of ions is greater.
|
If the electrolyte is strong, the molar conductivity slightly and linearly decreases as the square root of the concentration increases.
|
If the electrolyte is weak, the change in its degree of dissociation with concentration causes the molar conductivity to increase as concentration increases.
|
Chemistry
|
If the electrolyte is weak, the molar conductivity is much higher at high concentrations, when the number of ions is greater.
| 173 | 1 |
8d0cc36c-7b5e-46ed-8efe-d855a11008d8
|
2021
|
Regarding the lattice energy, we can assure that:
|
It is directly proportional to the interionic distance.
|
It is independent of the charges of the cation and the anion.
|
It is inversely proportional to the square of the interionic distance.
|
Chemistry
|
The Madelung constant depends on the type of crystal lattice.
| 175 | 3 |
cd4fcc16-313b-48bf-a245-9bc878908ed8
|
2021
|
The positive predictive value of a test is defined as:
|
The ratio of true positives divided by true positives plus false negatives.
|
The quotient of true positives divided by true positives plus false positives.
|
The ratio of true negatives divided by true negatives plus false negatives.
|
Chemistry
|
The sensitivity of the test divided by 1- specificity.
| 176 | 1 |
a81c8968-e50a-4a66-8986-4fc891d0b49d
|
2021
|
Pernicious anemia is one of the obvious symptoms of deficiency of:
|
Calcium.
|
Nickel.
|
Cobalt.
|
Chemistry
|
Magnesium.
| 177 | 4 |
628f59f9-bf3c-4463-8a1a-8e6a0a063036
|
2021
|
Which statement is correct?:
|
In cells, passive ion transport modes are produced.
|
In cells, both active and passive modes of ion transport occur.
|
In cells, secondary active ion transport modes are produced.
|
Chemistry
|
In cells, primary active ion transport modes are produced.
| 178 | 1 |
25dff5a0-6264-4d71-8fc3-484226205e48
|
2021
|
What is photoconductivity?
|
It is the increase in conductivity due to the rise in charge carriers as a result of electronic transitions induced by photons in which light is absorbed.
|
It is the color change that a solid presents when light shines on it.
|
It is the decrease in conductivity due to the increase in charge carriers as a result of electronic transitions induced by photons, in which light is emitted.
|
Chemistry
|
It is the increase in conductivity due to the increase in charge carriers as a result of electronic transitions induced by photons in which light is emitted.
| 179 | 2 |
2b8c21e5-1074-4295-8034-9652b2bb8783
|
2021
|
Which of the following is an enzyme containing selenium?:
|
Tyrosinase.
|
Dopamine beta-hydroxylase.
|
Glutathione peroxidase.
|
Chemistry
|
Urease.
| 180 | 4 |
93bfde3c-15ea-4441-a218-e0c960c84432
|
2021
|
If we want to study the accuracy of a method using a certified reference material, what statistical tests should we apply?
|
Student's t-test for comparing pairs of values.
|
Student's t-test for comparison of an experimental mean with the certified value.
|
Dixon's Q test for comparing pairs of values.
|
Chemistry
|
Fisher's F test to compare an experimental average with the certified value.
| 181 | 1 |
cbd7438d-8cbf-4283-981b-0127fa5d513c
|
2021
|
Which of the following statements is true when talking about a pair of diastereomers?:
|
They have specific rotations of opposite signs.
|
They have identical physiological properties.
|
They have different physical properties.
|
Chemistry
|
They have identical chemical properties (e.g., reactivity).
| 182 | 4 |
f1d334ac-cc46-4089-baa1-537e976c63a4
|
2021
|
The hemiacetal forms of carbohydrates are unconvertible in water. The equilibrium mixture may contain ฮฑ and ฮฒ anomers of furanose and pyranose structures. The change from one form to the equilibrium mixture is accompanied by a change in optical rotation called:
|
Mutarotation.
|
Anomeric effect.
|
Racemization.
|
Chemistry
|
Optical inversion.
| 183 | 2 |
21e46f87-33aa-44db-b525-7caa1b7f6f1c
|
2021
|
Which of the errors that can occur in a qualitative method is more serious when seeking the identification/quantification of a toxin?
|
Random errors.
|
False negatives.
|
Anomalous errors.
|
Chemistry
|
False positives.
| 184 | 1 |
915e087d-82fe-44f0-9b36-2bab4795d720
|
2021
|
Which of the following statements is correct in an enzymatic reaction?:
|
The enzyme changes the constant equilibrium of the reaction.
|
The enzyme shifts the reaction equilibrium to the right.
|
The enzyme alters the energy difference between reactants and products.
|
Chemistry
|
The enzyme increases the reaction rate.
| 185 | 3 |
8d99abcd-9725-4fb6-af29-4b594878ce7e
|
2021
|
On a solution containing Ti (IV), Fe (III), Bi (III) and Ni (II), solid ammonium chloride and concentrated ammonia solution are added to separate the cations from the 5th and 6th groups of the analytic march of sodium carbonate. Which of the cations will form an ammonium complex?
|
Fe (III).
|
Ti (IV).
|
Ni (II).
|
Chemistry
|
Bi (III).
| 1 | 4 |
ad786e54-1b6a-4be1-beee-7b005eb98f5d
|
2020
|
The use of microwave energy for the extraction of organic components in solid samples is widely spread as a clear alternative to Soxhlet extraction due to:
|
Its lower initial cost.
|
Its greater speed and efficiency.
|
That it is independent of the polarity of the extractant.
|
Chemistry
|
That the filtration stage of the extract is not necessary.
| 2 | 1 |
1209305c-786c-47e3-8a1b-1fbe9f50ba7a
|
2020
|
From the following parameters, indicate which one is not related to the reciprocal linear dispersion of a grating monochromator:
|
The wavelength of the radiation.
|
The diffraction order.
|
The focal distance of the monochromator.
|
Chemistry
|
The size of the striations or grooves of the network.
| 3 | 2 |
dc12afcf-0a24-4194-abc7-127fea9bd661
|
2020
|
Indicate the pH of a 0.05M ammonium cyanate solution if pKa(NH4+)=9.25 and pKa(HCno)=3.46:
|
9.89.
|
6.36.
|
7.00.
|
Chemistry
|
4.10.
| 4 | 1 |
8ed4ba06-f7d3-4075-a35c-2fd18ce0501e
|
2020
|
The efficiency of the columns used in high-performance liquid chromatography (HPLC) increases:
|
As the height of the plate becomes greater.
|
As the number of theoretical plates decreases.
|
As the length of the column decreases.
|
Chemistry
|
As the number of plates increases and the height of the plate decreases.
| 5 | 3 |
c2488af3-7524-4e88-b63e-44ecb822701f
|
2020
|
Cyclic Voltammetry:
|
It is characterized because the experiment is conducted using a connective method.
|
It is the most efficient and versatile electroanalytical technique for the mechanistic study of electrode reactions.
|
The indicator electrode is always a static Hg electrode.
|
Chemistry
|
It is a variation of differential pulse polarography.
| 6 | 1 |
456a16e6-dcc9-43c6-8ceb-ad66d14fa230
|
2020
|
Which of the following statements about electrospray ionization mass spectrometry (ESI/MS) is not correct?:
|
Ionization by electrospray is carried out under vacuum conditions.
|
It is a useful technique for the analysis of biomolecules such as polypeptides, proteins, and oligonucleotides.
|
It can easily be adapted to the direct introduction of a sample from a high-resolution liquid chromatography column or capillary electrophoresis.
|
Chemistry
|
In the process of electrospray, a small fragmentation occurs in large and thermally fragile biomolecules.
| 7 | 2 |
ce003240-86f2-4af9-bfe6-7ab78c2fed6e
|
2020
|
In capillary electrophoresis technique, one of the ways to introduce the sample into the separation capillary is through electrokinetic injection. How is this form of injection carried out?
|
Applying a pressure difference across the capillary.
|
Applying a potential difference between the ends of the capillary for an extended period of time.
|
Creating a vacuum at one end of the capillary.
|
Chemistry
|
Applying a potential difference between the ends of the capillary for a short period of time.
| 8 | 3 |
04193398-7a5f-44fb-89cf-2fbe9113c6d0
|
2020
|
Consider the oxidation-reduction reaction: Ce4+ + Fe2+ โ Ce3+ + Fe3+. Which of the following statements is true?:
|
The iron (II) ion is reduced to iron (III) ion.
|
The cerium (IV) ion is oxidized to Ce (III) ion.
|
The iron (II) ion is the reducing agent.
|
Chemistry
|
The cerium (IV) ion is the reducing agent.
| 9 | 4 |
0464c3ee-f359-417e-8e48-b8a98409aa63
|
2020
|
What is the value of the minimum decomposition voltage?
|
It is the leaving potential.
|
It is the voltage or anodic decomposition potential.
|
It is the value of the potential at which the intensity of the electrochemical reaction is zero.
|
Chemistry
|
It is the difference between the anodic decomposition potential and the cathodic decomposition potential.
| 10 | 3 |
ea720d00-d1a2-4e5f-89dd-1f61da642240
|
2020
|
What does the Hammett function (H0) describe?
|
Solubility.
|
Viscosity.
|
Acidity.
|
Chemistry
|
Electrochemical potential.
| 11 | 4 |
5265769f-940f-46d2-b88b-197367983c20
|
2020
|
To assess the accuracy of an analysis method, it is necessary:
|
Perform a calibration at different concentration levels with contrasted quality standards.
|
Repeatedly measure (n>11) the same sample and calculate its standard deviation.
|
Analyze a certified reference material and compare the results obtained in the laboratory with the certified values.
|
Chemistry
|
Study the effect of a sample component on the analytical signal.
| 12 | 4 |
1a502378-5fc5-48a3-a017-3019d199b23d
|
2020
|
What type of detectors are used in the ion chromatography technique with suppressor columns?
|
Spectrophotometric detectors.
|
Amperometric detectors.
|
Flame ionization detectors.
|
Chemistry
|
Conductivity Detectors.
| 13 | 3 |
fa9a22c5-3e32-43ce-ac93-729fcfea9578
|
2020
|
Which solvent has a greater elution strength in silica adsorption chromatography?
|
Toluene.
|
Hexane.
|
Methanol.
|
Chemistry
|
Acetone.
| 14 | 4 |
e7394d1e-28e1-44cd-bafa-484553aa6a95
|
2020
|
If the detection limit of a method for determining the content of As in drinking water is 2ยตgL-1 and the determination or quantification limit is 5ยตgL-1, we could ensure that the content of As in a sample of drinking water analyzed with this method is:
|
3 ยฑ 0.2 ยตg/L.
|
1 ยฑ 0.1 ยตgL-1.
|
10 ยฑ 1.1 ยตgL-1.
|
Chemistry
|
2 ยฑ 0.1 ยตg/L.
| 15 | 4 |
0f4001aa-494e-402e-a302-34ab3bafc6e2
|
2020
|
Which of the following pairs of compounds in solution does not form part of a buffer system?:
|
KCl/HCl.
|
Na2HPO4/NaH2PO4.
|
NH3/NH4NO3.
|
Chemistry
|
Na2CO3/NaHCO3.
| 16 | 2 |
81615cab-77c6-463c-899f-c8fb7272125d
|
2020
|
In high resolution liquid chromatography, in order to reduce the volume of the solvent and decrease the waste without sacrificing resolution, we could not use:
|
Instead of a column with a diameter of 4.6mm, use one of 3.0mm or 2.0mm.
|
Shorter columns with smaller diameter particles.
|
For isocratic separations, use an electronic recycler that sends the eluate to a recycling tank when no peak is eluted.
|
Chemistry
|
For gradient separations, use an electronic recycler that sends the eluate to a recycling tank when the peak is eluted.
| 17 | 3 |
b747c1d8-e10e-4dec-b23b-7d2e9ec5ef3d
|
2020
|
Which of the following statements is not related to the application limits of Beer's law?:
|
When the absorbing species undergoes association, dissociation, or reaction with the solvent.
|
When the concentration of the absorbing species is very high.
|
When the thickness of the cuvette used to carry out the measurement is greater than one.
|
Chemistry
|
The presence of parasitic radiation in the measuring instrument.
| 18 | 4 |
c2b796ad-5b40-4f8e-bf28-31bccdce4be8
|
2020
|
After analyzing the same sample in various laboratories, the lab that has worked with the most precision is the one that has obtained the result:
|
60 ยฑ 0.2 ยตgL-1.
|
55 ยฑ 2 ยตg/L.
|
57 ยฑ 0.02 ยตg/L.
|
Chemistry
|
50 ยฑ 10 ยตgL-1.
| 19 | 4 |
e411c0ae-400d-43c0-a9b9-266b475d2e42
|
2020
|
Indicate which of the following processes is not related to the operation of a laser:
|
The spontaneous emission.
|
Excitation through radiant energy.
|
The absorption.
|
Chemistry
|
The refraction.
| 20 | 3 |
4a52b471-7160-4154-ae50-eb33e995d17a
|
2020
|
Which of the following ion sources is not used in molecular mass spectrometry?:
|
Field Ionization.
|
Chemical Ionization.
|
Electronic ionization.
|
Chemistry
|
Ionization by nebulization.
| 21 | 3 |
84d6625f-642c-4f72-a61d-9ef41f1edc3d
|
2020
|
In chromatographic separations, the adjusted retention time of an analyte corresponds to:
|
The time the analyte spends in the mobile phase.
|
The time that the analyte spends in the stationary phase.
|
The time the analyte spends outside the chromatographic system.
|
Chemistry
|
The time that the analyte spends between the stationary phase and the mobile phase.
| 22 | 1 |
0059a43b-3dad-4ebf-8ff7-8ef30b419067
|
2020
|
Which of the following statements is not true regarding mass spectrometers?:
|
A quadrupole mass spectrometer has a constant resolution power, that is, the ions of m/z 100 and 101 are as separated as the ions m/z 500 and 501.
|
In a magnetic sector mass spectrometer, ions of different mass but with constant kinetic energy are separated by their trajectory through a magnetic field.
|
Ion trap spectrometers have a sensitivity 10 to 100 times lower than that of transmission quadrupole.
|
Chemistry
|
Time-of-flight mass spectrometers require a lower operating pressure than quadrupole and magnetic sector instruments.
| 23 | 4 |
d1495cd2-36b9-40a3-a17c-cacf8e38e3d1
|
2020
|
The flame ionization detector is used as a detection system in the separation technique called:
|
Liquid Chromatography.
|
Gas Chromatography.
|
Supercritical Fluid Chromatography.
|
Chemistry
|
Capillary electrophoresis.
| 24 | 1 |
74c04685-0729-4056-8327-4f9fab2e8873
|
2020
|
What is the indicator used in the titration of chloride with silver by the Mohr method?
|
A solution of potassium nitrate.
|
A potassium chloride solution.
|
A solution of potassium dichromate.
|
Chemistry
|
A solution of potassium chromate.
| 25 | 3 |
b8bd4096-a664-413a-9afc-7eebfa0f43fa
|
2020
|
Could an ultramicroelectrode be used in a medium of high resistance?
|
It would not be possible because the charging current would increase.
|
It would not be possible because the product iR would increase.
|
The product iR is independent of the electrode radius when used in a steady state.
|
Chemistry
|
It would not be possible due to the background noise it would generate.
| 26 | 4 |
a43f1763-6a19-4726-9cdf-fcc245297096
|
2020
|
Which of the following electrodes does not match with a metallic indicator electrode?:
|
Crystalline membrane electrodes.
|
Metallic redox indicator electrodes.
|
First-class electrodes.
|
Chemistry
|
Third class electrodes.
| 27 | 2 |
6f66cbf2-fbbc-4fe8-9644-046b75549f32
|
2020
|
Which of the following pattern recognition techniques uses dendrograms?
|
Principal Component Analysis.
|
Hierarchical method of cluster analysis.
|
Independent soft modeling of class analogy.
|
Chemistry
|
Linear discriminant analysis.
| 29 | 1 |
1b9678a1-2017-4e2e-bd5b-5f391cfd1b0b
|
2020
|
Regarding the "sodium error" in pH measurement using a glass electrode, select the correct one:
|
It occurs when the concentration of sodium is very low.
|
It can also be called "acid error".
|
The apparent pH is higher than the actual pH.
|
Chemistry
|
It takes place under alkaline conditions.
| 30 | 3 |
8d4ba45c-f3cd-43c0-8738-54a72d825e4f
|
2020
|
Which of the following species is not a primary standard for standardizing acids?:
|
Mercury II Oxide.
|
Potassium iodate.
|
Borax.
|
Chemistry
|
Sodium carbonate.
| 31 | 1 |
3638cba3-a995-4429-b1ab-0d9570bd5c6c
|
2020
|
What is the potential of a liquid junction?
|
It is a potential that only originates in the selective electrodes of liquid membrane.
|
It is the one that originates in a combined glass electrode.
|
It is a potential that originates when two electrolyte solutions are brought into contact.
|
Chemistry
|
It is a potential that only affects the metallic indicator electrodes.
| 32 | 4 |
51ea6583-1fe4-4451-b4eb-5ffbf496d5ce
|
2020
|
What are the coefficients a, b, and c for the following reduction reaction? aFe3+ + SnCl2 (aq)+ bCl- โcFe2+ + SnCl4 (aq):
|
a=2; b=2, c=2.
|
a=1; b=1, c=1.
|
a=3; b=2, c=2.
|
Chemistry
|
a=3; b=2, c=1.
| 33 | 2 |
35c1a2e3-5efd-40c3-8ca3-370a50b79ed9
|
2020
|
What does the irreversibility of an electrochemical reaction depend on?
|
The reaction will be more irreversible the smaller the KD/kO ratio is.
|
The reaction will be more irreversible the more different the values of the anodic and cathodic half-wave potentials are.
|
The reaction will be more irreversible the smaller the existing difference between the anodic and cathodic half-cell potential.
|
Chemistry
|
The reaction will be more irreversible the greater the value of kO.
| 34 | 1 |
62591ac5-63f6-4e2f-8a80-4b6f26e7f3ce
|
2020
|
Which of the following chromatographic detectors is based on the use of a radioactive compound?:
|
Thermal conductivity detector.
|
Electronic capture detector.
|
Mass spectrometer.
|
Chemistry
|
Flame ionization detector.
| 35 | 1 |
d62269ce-b1b0-46e4-a54d-d1e660fcc0e8
|
2020
|
The reaction between sodium iodide and cis-1-bromomethylcyclohexane in acetone results in:
|
cis-1-Iodo-3- methylcyclohexane.
|
trans-1-Iodo-3-methylcyclohexane.
|
3-Methyl-1-cyclohexene.
|
Chemistry
|
An equimolar mixture of cis- and trans-1-Iodo methylcyclohexane.
| 36 | 1 |
71488354-656f-43fe-9863-c305ec4cfff7
|
2020
|
Which of the following ethers cannot be prepared using a Williamson synthesis?:
|
Diphenyl ether (by reaction of PhONa + PhBr).
|
Diethyl ether (by reaction of EtONa + EtBr).
|
tButylmethyl ether (by reaction of tBuOK + Mel).
|
Chemistry
|
Ethylphenyl ether (by reaction of PhONa + EtBr).
| 37 | 2 |
66435c30-691a-45fe-bc20-6ff0b357937e
|
2020
|
Which of the following sentences, referring to the acidity of certain amines, is correct? (C6H5- NH2 = aniline; C6H13-NH2 = cyclohexylamine):
|
pKa(C6H5-NH3+) = 11.2; pKa(C6H13-NH3+) = 4.6.
|
pKa(C6H5-NH3+) = 4.6; pKa(C6H13-NH3+) = 11.2.
|
pKa(C6H5-NH3+) = 11.0; pKa(C6H13-NH3+) = 11.2.
|
Chemistry
|
pKa(C6H5-NH3+) = 4.6; pKa(C6H13-NH3+) = 4.8.
| 38 | 1 |
d04bb8ad-58b3-4d28-8e74-ad0f30ea5ea6
|
2020
|
Benzoic acid and 2-naphthol are compounds insoluble in water. The separation of a mixture of both compounds can be performed:
|
By treatment with a sodium bicarbonate solution (sodium hydrogen carbonate) to dissolve the benzoic acid.
|
By treating the mixture with a NaOH solution to dissolve the benzoic acid in water.
|
By treating with an aqueous solution of hydrochloric acid to dissolve the 2-naphthol.
|
Chemistry
|
By treatment with diethyl ether to dissolve benzoic acid.
| 39 | 2 |
9ae52274-0be2-4a46-aaf5-d3acfc65054f
|
2020
|
What product is formed when HBr is eliminated - through an E2 reaction - from (2S,3S)-2-bromo-3-phenylbutane?
|
Mixtures of (Z)-2-phenyl-2-butene and (E)-2-phenylbutene.
|
(E)-2-phenyl-2-butene.
|
(Z)-2-phenyl-2-butene.
|
Chemistry
|
(E)-3-phenyl-1-butene.
| 40 | 1 |
8161b7f9-f15f-4d4b-9e3f-e8e8fc59680b
|
2020
|
Suggest the appropriate reagents to transform benzene into cyclohexane:
|
NaBH4, methanol.
|
LiAlH4, ether.
|
H2, Pt.
|
Chemistry
|
H2SO4, HNO3.
| 41 | 4 |
5bcb9509-954a-4d74-82d0-b17de3a18d95
|
2020
|
The radical bromination of butane in C2 creates a molecule:
|
Olefinic.
|
Chiral.
|
Flat.
|
Chemistry
|
Heterocyclic.
| 42 | 1 |
62d4700a-fcd7-4867-baff-eb4862f0a6e8
|
2020
|
Carbocations and radicals contain a carbon atom with three substituents in one arrangement:
|
Trigonal planar.
|
Tetragonal plane.
|
Spherical.
|
Chemistry
|
Digonal plane.
| 43 | 2 |
c659120f-ea4a-447f-b834-c0fdd85f8b27
|
2020
|
Which of the following reactions is not regioselective?:
|
Electrophilic addition of hydrogen chloride to 2-methylpropene.
|
Chlorination of butane.
|
Reaction of 2-methylpropene with bromine in the presence of water.
|
Chemistry
|
Bromination of 2-methylpropane.
| 44 | 1 |
1f63e56c-4e01-4dbb-b240-837b04a0b252
|
2020
|
The compound cis-1,2-dibromocyclobutane:
|
It is an optically active compound.
|
It has two asymmetric carbons and is therefore a chiral compound.
|
It does not present asymmetric carbons and is therefore an achiral compound.
|
Chemistry
|
It is a meso compound and therefore an achiral compound.
| 45 | 3 |
2fc50590-392c-43e7-aedf-96573b7f0496
|
2020
|
In a Friedel-Crafts reaction, alkyl halides react with benzene in the presence of aluminum chloride to produce:
|
Olefins.
|
Alkylbenzenes.
|
Biphenyls.
|
Chemistry
|
Styrenes.
| 47 | 1 |
49c49681-14f0-4ef1-aff2-2b225dd8e09a
|
2020
|
In the reaction of cis- and trans-1-bromo-4-(1,1-dimethylethyl)cyclohexane with sodium methoxide:
|
4-(1,1-dimethylethyl)cyclohex-1-ene is produced, the reaction being faster if starting from the cis isomer of the starting substance.
|
Trans-4-(1,1-dimethylethyl)-1-methoxycyclohexane is produced.
|
A mixture of cis- and trans-4-(1,1-dimethylethyl)-1-methoxycyclohexane is produced.
|
Chemistry
|
4-(1,1-dimethylethyl)cyclohex-1-ene is produced, with the reaction being faster if it starts from the trans isomer of the starting substance.
| 48 | 2 |
26dfba8e-921d-4eba-82d0-d8d112ec1128
|
2020
|
Hydrogen cyanide is reversibly added to carbonyl groups to form adducts, commonly referred to as:
|
Amides.
|
Diazonium salts.
|
Hydrazines.
|
Chemistry
|
Cyanohydrins.
| 49 | 3 |
ce9b6a4d-32ac-496a-913a-569cd2cd4fbb
|
2020
|
What is the bromination product of cyclohexene under non-radical conditions?
|
cis-1,2-dibromocyclohexane.
|
Racemic trans-1,2-dibromocyclohexane.
|
1,2-dibromocyclohexene.
|
Chemistry
|
Racemic 3-bromocyclohexene.
| 50 | 1 |
e4e1d138-f376-4cf9-9bed-1356b4e1d08f
|
2020
|
The diazonium group on a benzene ring, when treated with hypophosphorous acid, is replaced by an atom of:
|
Phosphorus.
|
Nitrogen.
|
Hydrogen.
|
Chemistry
|
Oxygen.
| 51 | 4 |
c69e24fa-a2ff-4d5d-8039-a54260fb670c
|
2020
|
What is the name of the reaction that converts ethyl 3-oxobutanoate to 3-substituted methyl ketones or 3,3-disubstituted methyl ketones?
|
Acetoacetic synthesis.
|
Malonic synthesis.
|
Aldol condensation.
|
Chemistry
|
Claisen Condensation.
| 52 | 2 |
6b5a5006-1a57-4580-ba1a-1e7a12a0a50a
|
2020
|
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