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The approximate pH range for the color change of methyl red indicator (Ka = 1.0 x 10^-5) is: | 4.2 to 6.3. | 3.1 to 4.4. | 6.2 to 7.8. | Chemistry | 5.2 to 6.8. | 132 | 2 | 40b0f61c-2146-4e3b-a157-7721b3a1b0f2 | 2024 |
In the Inductively Coupled Plasma (ICP) technique, the sample undergoes the following stages: | Combustion, desolvation, atomization, and ionization. | Stabilization, combustion, atomization and ionization. | Desolvation, combustion, atomization, and stabilization. | Chemistry | Nebulization, desolvation, volatilization and ionization. | 133 | 3 | 2f36bc40-0b8d-4756-a872-1351e819d7c5 | 2024 |
In adsorption chromatography, the eluent strength or elutropic strength (εº) is used as an index to assess the potency of a solvent. The eluent strength: | It is defined as 0 for pentane when the adsorbent is silica. | It depends solely on the solvent used. | It is no longer in use because it works worse than the polarity index (P') to explain the power of a solvent in this type of chromatography. | Chemistry | It does not influence the elution speed. | 134 | 2 | 73ebbf6b-38a9-4de4-86ec-fb5a8cb56ad1 | 2024 |
What type of radiation is usually used for the excitation of the sample in Raman spectroscopy? | Visible radiation. | Microwave radiation. | Gamma radiation. | Chemistry | X Radiation. | 135 | 2 | 7d029f29-7197-4334-932a-085f09f1f725 | 2024 |
In liquid chromatography, the packing of the pre-column should have the following in relation to the packing of the analytical column: | Different composition and smaller particle size. | Different composition and same particle size. | Similar composition and smaller particle size. | Chemistry | Similar composition and larger particle size. | 136 | 3 | 94fb40c5-344d-4b9b-bc41-b40ca8ae2d6c | 2024 |
What is the standard potential of the following reaction, if we know that Eº(Pb4+/Pb2+) = 1.69 V and Eº(Cu2+/Cu+) = 0.34 V? Pb4+ + 2Cu+ → Pb2+ + 2Cu2+ | + 1.01 V. | + 1.35 V. | + 2.03 V. | Chemistry | - 1.35 V. | 137 | 1 | 15241861-3cba-4e79-bafe-e56055a45d8e | 2024 |
In potentiometry, what is a second-class electrode? | Calomel electrode used as a reference electrode. | Metallic electrode in direct equilibrium with its cation in solution. | Metallic electrode that responds to the activity of an anion with which it forms a precipitate or a stable complex ion. | Chemistry | Electrode constructed with platinum, gold, palladium or other inert metals. | 138 | 4 | 94c96747-ab25-4e35-a018-4b21645fb6a0 | 2024 |
When is instrumental calibration using the internal standard method used? | When one wants to compensate for the fluctuations of the analytical response due to instrumental measurements or the analysis method. | When the composition of the sample is unknown or complex and affects the analytical signal. | For the analysis of solid samples using IR spectrometry. | Chemistry | When matrix modifiers are used in atomic absorption spectrometry with electrothermal atomization. | 139 | 2 | bc9e2c09-58ef-436a-a079-2d19d1ca185a | 2024 |
What is the selectivity of an analysis method? | Minimum amount of analyte that provides a signal significantly different from the blank signal. | Change that a certain analytical signal undergoes per unit of concentration. | Degree of interference produced by the compounds that accompany the analyte in the sample. | Chemistry | The ability of a method to remain unaffected by slight changes in the procedure, the quality of the reagents, or the environmental conditions. | 140 | 4 | 60985577-4de7-4d64-96a9-04f963fc7350 | 2024 |
What is the indicator used in the determination of chlorides using the Volhard method? | Fluorescein. | Na2CrO4. | Fe3+. | Chemistry | Phenolphthalein. | 141 | 4 | db1bfb31-dbdd-4713-a488-18cdf3ebf66d | 2024 |
What is the pH of an aqueous solution of KOH 10-8 M at 25ºC? | 7. | 6. | 14. | Chemistry | 8. | 142 | 2 | 0bd1064e-3331-4bf0-9347-90f614b1876f | 2024 |
Which of the following aqueous solutions has a lower pH value?: | HF 0.1 M (pKa = 3.4) | HBr 0.001 M. | NH4Cl 0.05 M (pKa = 9.25) | Chemistry | CH3COOH 0.1 M (pKa = 4.75) | 143 | 2 | 0a01ecaa-f2cf-4ee8-bdbc-dca60b68fc16 | 2024 |
In the microwave-assisted extraction of an analyte in a solid sample: | The transfer of one or more substances occurs between two immiscible liquid phases that are put into contact with each other. | A quantitative extraction of compounds is achieved after subjecting it to reflux for 12-24 h, using 200-300 mL of solvent. | Solvents with high dielectric constant are good extractants because they absorb microwave radiation. | Chemistry | The matrix is destroyed to leave the analyte in solution. | 144 | 4 | 8701575a-4b31-4105-b2fd-b6bfdb8f85da | 2024 |
The exposure of metals to a flame produces colors of specific wavelengths that allow their identification. Which of the following metals produces yellow light when exposed to a flame?: | Barium. | Sodium. | Copper. | Chemistry | Strontium. | 145 | 1 | 7f08fc42-99c3-4b09-b542-743b6d8332c0 | 2024 |
Which of these mixtures will be a buffer solution if dissolved in 1 L of water?: | 0.5 moles of NH3 and 0.5 moles of HCl. | 0.2 moles of NaOH and 0.2 moles of HBr. | 0.4 moles of CH3COOH and 0.2 moles of NaOH. | Chemistry | 0.3 moles of KOH and 0.2 moles of HF. | 146 | 4 | c4f37934-ec6b-48b1-9770-703d377b5acf | 2024 |
Regarding the properties of a quantitative instrumental method, it is true that: | If a result is below the quantification limit, it is recommended to dilify the sample and reanalyze it. | The quantification limit is usually lower than the detection limit. | The linear response range of a method goes from the detection limit to the quantification limit. | Chemistry | Analytical sensitivity is defined as the slope of the calibration curve. | 147 | 3 | 17b1910c-d744-4c34-bdac-5eff1afb3b8d | 2024 |
Which of the following species causes isobaric interference with 56Fe+ in inductively coupled plasma mass spectrometry?: | ArC+ | ArO+ | ArN+ | Chemistry | ArH+ | 148 | 1 | 8c52c278-d2ea-47f0-b5b7-87d4c146df21 | 2024 |
Which mass analyzer is based on the following principle?: "Storage of ions in a space defined by electrodes. The electric field sequentially expels the ions as their m/z values increase": | Flight time. | Quadrupole. | Magnetic sector. | Chemistry | Ion trap. | 149 | 3 | 6475163f-373f-4963-a5da-4e9be2b9a172 | 2024 |
The ion-selective electrode that incorporates the antibiotic valinomycin is used to determine: | Calcium. | Chlorine. | Sodium. | Chemistry | Potassium. | 150 | 3 | 3cf5c7c5-27bf-4d9a-a0d6-38926ec87665 | 2024 |
If the distribution coefficient (KD) of a solute in a chromatographic system is one, what is being indicated?: | That is distributed equally between stationary phase and mobile phase. | That does not manage to be retained in the column. | That the solute is partially eluted. | Chemistry | That 100% of the substance is in the stationary phase. | 151 | 2 | baf744a8-589b-4723-b68a-1ffefabe1879 | 2024 |
In the "split" injection type, which is used in gas chromatography: | The injection is performed with sample division. | The entirety of the injected sample is directed towards the column. | It is used with samples that have a low concentration of the analyte to be determined. | Chemistry | The detection limits that are achieved are lower. | 152 | 2 | e97bf65c-7974-4174-a440-a552d01c4dd2 | 2024 |
The graphite chamber is used in: | Atomic absorption spectroscopy. | Polarography. | High performance liquid chromatography. | Chemistry | Inductively coupled plasma mass spectrometry. | 153 | 2 | e50947a7-a951-4bd3-99d7-92edba11805d | 2024 |
Which of the following is not one of the general methods to carry out titrations with EDTA?: | Titration by displacement. | Direct titration. | Back titration. | Chemistry | Titration by neutralization. | 154 | 3 | 6ee1c569-1bc4-4790-b392-a6b2ec5bf3b2 | 2024 |
What property is sought to be minimized in gravimetry to obtain crystalline precipitates? | Solute concentration. | Temperature. | pH. | Chemistry | Solubility. | 155 | 2 | 49935953-0aa2-4dff-8a8c-7679fed809c7 | 2024 |
Amperometry is used to measure: | The potential difference between two electrodes. | The electric current generated by an electrochemical reaction. | The response of a chemical substance to different levels of potential. | Chemistry | The amount of electricity needed for a redox reaction. | 156 | 1 | b1e6df45-5fad-4849-b64d-f085c759c5d7 | 2024 |
Regarding derivatization, commonly used in gas chromatography, it is true that: | It is carried out exclusively with 2,4-dinitrophenylhydrazine and derivatives. | Reduces the analysis time. | Allows the analysis of non-volatile compounds. | Chemistry | It does not chemically modify the analyte. | 157 | 4 | cf39e478-5c9c-4786-8e9f-bc1a601d5a8b | 2024 |
In gel filtration chromatography (molecular exclusion), the molecules that elute last are those that have: | Diameter larger than the average size of the filler pores. | Diameter smaller than the average size of the filler pores. | Ionized groups. | Chemistry | Higher molecular weight. | 158 | 1 | 7d9e3d7c-c759-408d-8501-82f54938ce61 | 2024 |
In an electrochemical cell, which of the following examples represents a typical anodic reaction?: | Ag⁺ + e⁻ → Ag(s)
Translation: Silver ion + electron → solid silver | Cu(s) → Cu²⁺ + 2e⁻. | O2 + 4H+ + 4e⁻ → 2H2O. | Chemistry | Fe³⁺ → Fe²⁺ + e⁻. | 159 | 1 | 6e1cccc9-d733-42ef-8723-1cf65a591d2a | 2024 |
The study of proteins using circular dichroism techniques allows us to understand their: | Primary sequence. | Secondary structure. | Catalytic activity. | Chemistry | Molecular weight. | 160 | 1 | 31814afb-6ef1-40bc-87fc-dcf42fcbac17 | 2024 |
In a second order chemical reaction, the half-life (t1/2) is related to the initial concentration of the reactant: | Independent. | Directly proportional. | Inversely proportional to its square. | Chemistry | Inversely proportional. | 161 | 3 | 53175719-4559-4071-94f7-05199880392d | 2024 |
Considering that F is the number of phases present in a system, C is the number of different chemical species, and L is the number of degrees of freedom, what is the correct expression for the phase rule in a system without a chemical reaction? | F + L = C + 2. | F + L = C - 2. | F + L = C + 3. | Chemistry | F + L = C - 3. | 162 | 2 | ea86f005-f4c0-40d5-85ce-72976f5e9cfb | 2024 |
The temperature above which the gaseous phase of a substance can no longer be liquefied by increasing pressure is called: | Triple point temperature. | Glass transition temperature. | Critical temperature. | Chemistry | Liquefaction temperature. | 163 | 4 | 5700b250-8df1-4b3c-9bb0-b3ee4b3fcd35 | 2024 |
What allows the calculation of the intensity of transitions to different vibrational levels that occur together with molecular electronic transitions? | The Pauli Principle. | The vibration selection rules. | The frequency of the incident radiation. | Chemistry | The Franck-Condon Principle. | 164 | 3 | 829501fa-cfa8-4f3c-8cfc-bc05fbb9515e | 2024 |
Which of the following compounds has the highest lattice energy value?: | LiF. | NaCl. | MgO. | Chemistry | MgCl2. | 165 | 4 | 6d3dd453-b624-4678-9a69-27eda7da6513 | 2024 |
According to the Debye-Hückel limiting law, the average ionic activity coefficient: | It is always negative. | It can have any value. | It is always greater than one. | Chemistry | It is always less than one. | 166 | 3 | 506a7b7a-8d63-4f8f-a958-5978a8398abb | 2024 |
The second law of thermodynamics PREVENTS the entropy of a: | Open system decrease. | Closed system increases. | Isolated system increases. | Chemistry | Isolated system decreases. | 167 | 3 | 9700afbe-95d6-486b-9b8c-a2454a816b17 | 2024 |
The isotope 90Sr can be incorporated in place of calcium in the bones. This isotope has a half-life period of 29 years. Let's assume that a newborn initially absorbs 1.00 µg of 90Sr. How much 90Sr will remain in its body after 58 years of life, assuming that no metabolic loss occurs? | 0.25 µg. | 0 µg. | 0.75 µg. | Chemistry | 0.50 µg. | 168 | 2 | 5efe8980-2646-4bb7-b1da-bc98dbb6ccef | 2024 |
Indicate which of the following properties is not a colligative property: | The decrease in vapor pressure. | The variation of pH. | The lowering of the freezing point. | Chemistry | The osmotic pressure. | 169 | 1 | d90d1284-6c9e-43bd-aceb-57d5596d7857 | 2024 |
Which of the following statements is false?: | For a laminar flow of a liquid in a cylindrical tube, the flow rate is maximum at the center of the tube. | For a laminar flow of a liquid in a cylindrical tube, the flow rate is the same at all points of a plane perpendicular to the axis of the tube. | When the temperature increases, the viscosity of liquids usually decreases while that of gases increases. | Chemistry | Newton's law of viscosity is not applicable to very high flow rates. | 170 | 1 | e29fba81-48b5-4d48-b3eb-744ecde965fa | 2024 |
In quantum mechanics, the necessary condition for the eigenvalues of two operators to be simultaneously determined in a non-degenerate system is that: | The operators commute. | The operators are Hermitian. | The operators should be linear. | Chemistry | They can always be determined. | 171 | 2 | 7efb1361-b9ef-4ce0-b6dc-b2caa3540bcb | 2024 |
The term "liquid crystal" refers to a state that is intermediate between: | Crystalline solid and amorphous liquid. | Crystalline solid and vapor. | A crystal submerged in a liquid. | Chemistry | Amorphous liquid and vapor. | 172 | 2 | 60e9507e-3d20-4abb-9ab0-3a358abfba36 | 2024 |
Let it be an ideal mixture of two liquids A and B, of which A is the most volatile. It is correct to say that: | The boiling temperature of the mixture depends only on the external pressure. | The boiling temperature of the mixture is higher the greater the molar fraction of A in the liquid. | Through simple distillation, pure A can be obtained but not pure B. | Chemistry | The boiling temperature of the mixture is lower than that of pure B and higher than that of pure A. | 173 | 3 | e21fa863-6303-4813-85ec-3b262f01e3c8 | 2024 |
Taking into account the bond order: | The C2 molecule is unstable. | The ion C2– is more stable than the C2 molecule. | The ion C2– has the same stability as the C2 molecule. | Chemistry | The ion C2– is less stable than the C2 molecule. | 174 | 1 | a2f95e72-d105-4f85-852d-05330fff6d93 | 2024 |
Regarding the acid-base equilibrium, indicate the correct statement: | The pH of a neutral solution is 7.0 and does not depend on the temperature. | If pKa(HA) < pKa(HB), then A- is a stronger base than B-. | An aqueous solution of ammonium chloride exhibits acidic or basic character depending on the salt concentration. | Chemistry | An increase in temperature results in an increase in the hydrolysis constant. | 175 | 3 | cc06bd75-8654-4844-aa3a-c5d95e628537 | 2024 |
In which of the following processes is the entropy increase positive? | I2 (g) → I2 (s) | KCl (aq) → KCl (s) | N2 (g) + 3H2 (g) → 2NH3 (g) | Chemistry | NH4Cl (s) → NH3 (g) + HCl (g) | 176 | 3 | ffff8084-b1fe-42c0-96fc-04ed7ba53856 | 2024 |
Experimentally, there is a dependency of the speed of a chemical reaction, v, on the temperature, T, in such a way that increasing T increases v. Recalling that the speed of a reaction is proportional to its rate constant, k and that A is a constant, R is the universal gas constant and EA is the activation energy and is always positive, indicate which equation fits the experimental fact: | k = -A exp(-EA/RT) | k = A exp(-EA/RT) | k = -A exp(EA/RT) | Chemistry | k = A exp(EA/RT) | 177 | 1 | 75d8b343-86a1-431b-a881-de43b8d737d3 | 2024 |
An ideal gas expands against the vacuum inside a container with adiabatic walls. As a result of this process: | The gas is heated. | The temperature of the gas does not change. | The final temperature of the gas depends on the ratio between the final volume and the initial volume. | Chemistry | The gas cools down. | 178 | 1 | 86e9d53b-9e56-4a6c-857a-e44d22e58792 | 2024 |
The expected value for the molar heat capacity at constant pressure, CP, for a monoatomic ideal gas is (R represents the gas constant): | CP = 3R/2. | CP = R. | CP = 7R/2. | Chemistry | CP = 5R/2. | 179 | 3 | 96daa767-99da-4373-aae0-b8797482fe0d | 2024 |
At 298 K, once the equilibrium is established at the air/water interface at normal atmospheric pressure, it is found that the solubility of O2 in water is 0.29 mmol kg-1. If the air is replaced by pure O2(g) at the same temperature and pressure, what would be the approximate solubility of O2 in water? | 0.58 mmol kg-1. | 0.29 mmol kg-1. | 2.85 mmol kg-1. | Chemistry | 1.28 mmol kg-1. | 181 | 3 | 84f82754-8a66-432d-92b7-baf2afa37098 | 2024 |
Indicate which formula is correct in thermodynamics: | In an isothermal process: ΔU ≠ 0. | U = δQ + δW. | G = H - TS. | Chemistry | H = U - PV. | 182 | 4 | aacc37bb-cd75-4875-b5b3-4063946ef14a | 2024 |
How does the first ionization potential vary as we move along a group in the Periodic Table? | Decreases. | It is constant. | The first ionization potential of an element coincides with the second ionization potential of the subsequent element. | Chemistry | Increase. | 183 | 2 | 2d2eb42a-a9ef-417a-a38c-92c2c6312215 | 2024 |
What is the consequence of adding a plasticizer to a thermoplastic material? | Increase the glass transition temperature of the polymer. | Decrease the glass transition temperature of the polymer. | It makes the material more rigid without modifying the glass transition temperature. | Chemistry | It has no effect since thermoplastic substances do not have a glass transition temperature. | 184 | 1 | 99946f55-239a-48a8-904c-20ea2ce2a51a | 2024 |
In which of the following molecules is the distance between the carbon atoms the smallest? | Ethene. | Ethanol. | Benzene. | Chemistry | Ethane. | 185 | 2 | c8faa6e2-fcc8-417f-b872-4b39ef2e9036 | 2024 |
In what type of substances does electrical conductivity decrease as the temperature increases? | Insulators. | Semiconductors. | Metals. | Chemistry | This situation does not occur with any type of substances. | 186 | 4 | 795dd1d9-0292-43c8-9ed2-0872f4839e0e | 2024 |
In addition to the concentration of the active ionic species, on what does the so-called polarization overpotential depend on? | Current density and concentration of the remainder of active ionic species. | Current density and diffusion coefficient of the active ionic species. | Current density and electrode polarizability. | Chemistry | On the solid or liquid nature of the electrode. | 187 | 1 | 671dcb0a-22bc-471d-98f4-e25c95a6d531 | 2024 |
What is an intensive thermodynamic property? | One that does not depend on the amount of matter in the system. | One whose value is equal to the sum of the corresponding values of different parts of the system. | One that is independent of the state of the system. | Chemistry | One that depends on the amount of matter in the system. | 188 | 2 | 404f71bc-645a-4229-b341-acc59b97ec41 | 2024 |
What is the internal conversion process in a molecule? | The decay of the excited state to the ground state of the molecule through a non-radiative process in the absence of a chemical reaction. | The decay of the excited state of the molecule through a radiant process in the absence of a chemical reaction. | The process that is always prior to molecular phosphorescence. | Chemistry | The decay of the excited state of the molecule through a radiant process via collision with another species. | 189 | 2 | da5348e2-51e1-44a5-b395-838430738466 | 2024 |
In a catalytic process: | Decrease the reaction order. | Decreases the activation energy. | The equilibrium constant increases. | Chemistry | The rate constant decreases. | 190 | 1 | 6ccc363a-db56-449c-a163-4e54510ed007 | 2024 |
When a liquid completely wets a surface, the liquid-surface-air contact angle is: | Greater than 90º and less than 180º. | Equal to 180º. | Equal to 0º. | Chemistry | Greater than 0º and less than or equal to 90º. | 191 | 4 | 70e7d311-ede5-4483-b251-1906c2965eed | 2024 |
In a first-order reaction, where the rate only depends on reactant A, it holds that: | The graphical representation of 1/[A] vs t is linear. | The graphical representation of ln([A]0/[A]) vs t is linear. | The slope of the graphical representation of [A] vs t is the rate constant of the reaction, but with its sign changed. | Chemistry | The graphical representation of 1/[A]2 vs t is linear. | 192 | 1 | 769a6cb4-e4c9-4f9b-ac08-61f754a6a3f3 | 2024 |
The Maxwell-Boltzmann statistics are valid for: | Systems of indistinguishable particles without quantum restrictions. | Systems of indistinguishable particles with quantum restrictions. | Any type of particle. | Chemistry | Discernible particle systems. | 193 | 3 | 5d5bc10e-83b7-470c-86e9-c364f685edc9 | 2024 |
The Eyring equation is derived from the Transition State Theory. By conducting experiments at different temperatures using this equation, we can obtain: | The diffusion coefficient. | The frequency of collisions. | The enthalpy and entropy of activation. | Chemistry | The order of reaction. | 194 | 4 | 8432d621-c637-4073-80d2-f19e05b07861 | 2024 |
For a certain chemical reaction, it is found that, in the temperature range between 100ºC and 300ºC, both the standard Gibbs reaction energy, ΔrGº, and the standard reaction enthalpy, ΔrHº, are positive quantities. Which of the following pairs of equilibrium constants is compatible with the previous data?: | K(100ºC) = 4.85; K(300ºC) = 2.45. | K(100ºC) = 2.45; K(300ºC) = 4.85. | K(100ºC) = 0.045; K(300ºC) = 0.085. | Chemistry | K(100ºC) = 0.085; K(300ºC) = 0.045. | 195 | 4 | 994bc402-8088-4b96-8e5f-9930aad137a6 | 2024 |
A chemical reaction, 𝑹 𝒌 → 𝑷 (k represents the rate constant), is catalyzed by substance C if the following is true: | R + C → P , with k' > k. | R + C → P + C. | 𝑅 + 𝐶 → 𝑃 + 𝐶 , with k' > k. | Chemistry | R + C → P4 + P6 + C, with k' > k. | 196 | 4 | 958692b2-299d-458b-8dfd-e73a5aa7f950 | 2024 |
Green hydrogen is obtained through the electrolysis of water. What reaction describes the process?: | 2H2O (l) → 2H2 (g) + O2 (g) | 2H2O (l) + 2e– → H2 (g) + 2OH– (aq) | Zn (s) + 2HCl (aq) → H2 (g) + ZnCl2 (aq) | Chemistry | CH4 (g) + 2H2O (l) → 4H2 (g) + O2 (g) | 197 | 2 | c29e6541-d3d6-4aca-a980-d400f37e6a3a | 2024 |
Which processes occur at a faster rate, fluorescence or phosphorescence? | Both occur at the same speed. | The phosphorescence ones. | The ones of fluorescence. | Chemistry | It cannot be determined a priori. | 198 | 4 | 5a59cd2c-001b-492e-91e3-2ce0e64f2b0f | 2024 |
In the Born-Oppenheimer approximation, it is assumed that the nuclear and electronic movements in a molecule: | They are coupled due to the difference in mass of the nuclei and the electrons. | They are decoupled due to the mass difference of the nuclei and the electrons. | They are coupled due to the charge difference between the nuclei and an electron. | Chemistry | They are uncoupled due to the charge difference between the nuclei and an electron. | 199 | 1 | f6c7747b-d276-4081-9993-444265dbe29f | 2024 |
Which thermodynamic variables (pressure, volume, temperature) remain invariant in an adiabatic process? | The pressure and the volume. | None. | The temperature and the volume. | Chemistry | The temperature. | 200 | 1 | be6e79b8-c2fb-4327-a524-3845eee0d647 | 2024 |
Which of the following compounds, with similar molecular masses, has a higher boiling point?: | Propanol. | Acetic acid. | Methyl methanoate. | Chemistry | Ethanamide. | 201 | 3 | db4ba0d7-3f3a-4dcd-8b94-46756d952d83 | 2024 |
Which of the following molecules is used in medicine as a biomarker for acute coronary syndrome or acute myocardial infarction?: | C-reactive protein. | Troponin. | Creatinine. | Chemistry | Alanine aminotransferase. | 202 | 1 | 7aa05f52-d91f-4c69-a954-3af00995beb5 | 2024 |
In the usual analysis of Nuclear Magnetic Resonance spectra, the condition of weak coupling (first-order spectra) is considered. Under what conditions can we encounter strong coupling spectra (second-order)? | We never find this type of spectra. | When we use equipment with high magnetic field intensities. | When the differences between the chemical shifts of the nuclei are comparable to those due to spin-spin coupling. | Chemistry | When the differences between the chemical shifts of the nuclei are much greater than those due to spin-spin coupling. | 203 | 4 | bb923f1b-d9c0-4163-9645-4251f3597141 | 2024 |
What do the nitrogens from amines and amides of organic substances convert into in the first step of their determination by the Kjeldahl method? | NH4+ | NO3-. | CO(NH2)2. | Chemistry | NO2-. | 204 | 2 | 2266a535-d681-40b9-b6ae-f2d6373dd2d8 | 2024 |
Fick's First Law: | Relates the flow of matter with the diffusion coefficient and the temperature gradient. | Relates the heat flow with the diffusion coefficient and the temperature gradient. | Relate the flow of matter with the diffusion coefficient and the concentration gradient. | Chemistry | Relates the heat flow with the diffusion coefficient and the concentration gradient. | 205 | 4 | 490da002-9be7-42ef-a292-c777ef3dc075 | 2024 |
Which of the following oxides is considered amphoteric?: | Dialuminum trioxide. | Carbon dioxide. | Diboron Trioxide. | Chemistry | Magnesium oxide. | 206 | 2 | a61a6eae-ac7b-4e4e-bada-98541a2f062a | 2024 |
A compound with formula C5H12O shows, in the 1H-NMR spectrum in CDCl3, the existence of two unique peaks at 3.2s (3H) and 1.2s (9H). This would be: | 2-isopropoxypropane (diisopropyl ether). | 1,2-dimethyl-1-propanol. | 2-methoxy-2-methylpropane (t-butyl methyl ether). | Chemistry | 3-methyl-2-butanol. | 207 | 4 | f0d57df4-1537-4c90-a4eb-afc352780d92 | 2024 |
How should biological tissue samples be preserved if one wishes to determine the content of volatile compounds in them until their analysis? | They should be kept in perfectly sealed containers at room temperature in a desiccator. | They must be kept refrigerated (in a fridge at 4ºC). | They should be kept in a dry place and protected from light. | Chemistry | They must be kept frozen (-20ºC). | 208 | 3 | ac0173b6-9722-416e-9fed-6f98353ed3ef | 2024 |
In a saturated aqueous solution of lead (II) chloride, the relationship between the solubility product (Kps) and the solubility (S) is: | Kps = 3S. | Kps = 2S. | Kps = 4S3. | Chemistry | Kps = 2S2. | 209 | 4 | cad1f217-838b-404f-8965-b8e99afac94f | 2024 |
In alcoholism, hypoglycemia can be caused as a result of the hepatic metabolism of ethanol, and this is due to: | Increase in the reduction of pyruvate to lactate. | Increase in the formation of ketone bodies. | Reduction in the speed of the Krebs cycle. | Chemistry | Increase in β-oxidation. | 210 | 2 | 25a966af-0cee-4cf4-bb35-2362f0d7a731 | 2024 |
What species is determined when a sample containing Ca2+ and Mg2+ is evaluated with EDTA at pH=12 and murexide as an indicator? | Mg2+. | Ca2+. | Neither of the two species. | Chemistry | Ca2+ + Mg2+. | 1 | 1 | 27dd88da-6e00-4825-8521-c4ba3f49bd35 | 2023 |
If we evaluate 50.0 mL of 0.050 M HCl with 0.100 M NaOH, what is the pH value at the equivalence point? | 2. | 1. | 7. | Chemistry | 5. | 2 | 4 | 8aee560f-4b9d-4dee-ba7a-b3d4f544b4fe | 2023 |
In an aqueous solution of KHA, what is the relationship between the concentration of the potassium ion and the concentration of the rest of the species? | [K+]= [H2A] + [HA-] + [A2-]. | [K+] = [HA-] + [OH-]. | [K+] = [HA-] + [OH-] + 2[A2-]. | Chemistry | [K+] = [HA-] + [OH-] + 2[A2-]. | 3 | 2 | 522e6f1b-5cdd-42c4-a645-73b0f9bf84e7 | 2023 |
What process controls the current in conventional polarography? | Convection. | Diffusion. | The conduction. | Chemistry | The adsorption. | 4 | 1 | 95026c19-31cb-4b11-88cb-d889e72818c5 | 2023 |
Which of the following statements is false in relation to internal standard calibration?: | Known quantities of the internal standard are added to the samples and to the calibration patterns. | It applies when, among successive measures, it is difficult to maintain any of the operating parameters or reproduce the amount of sample subjected to the measurement process. | The concentration of the analyte of interest is obtained by extrapolating the regression line to the point on the x-axis (amount of analyte added) where the measured analytical signal is zero. | Chemistry | The internal standard must exhibit, in the analytical process, a behavior analogous to that of the analyte to be determined. | 5 | 4 | 11aa2dee-150e-48f6-92c8-d6b4eb7d55b0 | 2023 |
A 0.1 M solution of a weak monoprotic acid (HA) has a pH of 4. It is met that: | pKa = 5. | pKa = 2. | pKa = 9. | Chemistry | pKa = 7. | 6 | 3 | adfd206f-4e5a-4cc5-b779-8a75da827e17 | 2023 |
Which of the following statements is false in relation to iodometry?: | The titrating reagent of the generated iodine is a standard solution of reducing nature, generally sodium thiosulfate. | It is a method that involves the valuation of the iodine generated in the reaction between an oxidant analyte and an excess of iodide. | The endpoint of the iodometric titration is indicated by the appearance of blue color. | Chemistry | The starch (indicator) is added near the endpoint of the titration when most of the iodine has been titrated. | 7 | 4 | e4e01fcb-43a8-4ed6-ac5d-10d1adae8a46 | 2023 |
Pressure variations in supercritical fluid chromatography: | They have a very marked effect on the retention factor k. | They do not have any effect on the retention times of the separated species. | The obtained chromatograms significantly worsen. | Chemistry | They occur during the separation due to decomposition phenomena of the fluids used. | 8 | 2 | 2ce36fcc-b53f-4153-b7e4-40524350b17a | 2023 |
The Karl Fischer titration is related to: | The potentiometric determination of halides. | The determination of the hardness of a mineral water. | The determination of the isoelectric point of a protein. | Chemistry | The determination of water. | 9 | 3 | 78cfd77a-ff5e-481d-b168-244c13948f9c | 2023 |
Identify the substance most often used as the mobile phase in supercritical fluid chromatography: | Methanol. | Water. | Carbon dioxide. | Chemistry | Hexane. | 10 | 4 | 483728e4-8356-4dd0-adc3-d4570eeb1265 | 2023 |
Fourier Transform Infrared Spectrometers: | Czerny-Turner monochromators are used to achieve spectra with very low noise levels. | They do not have a dispersing element and all wavelengths are detected and measured simultaneously. | They incorporate a cooled CCD type detector as a key element in their operation. | Chemistry | They have a slower response rate and worse sensitivity than scanning instruments, although they allow for multi-element analysis. | 11 | 1 | 4c9f1d1e-1912-49ab-bacf-951f0191dae8 | 2023 |
What does gradient elution in high performance liquid chromatography (HPLC) consist of? | In the variation of the mobile phase flow during chromatographic separation. | In the variation of the chromatographic column temperature during the analysis in a continuous and staggered manner. | In the variation of the mobile phase composition during the analysis in a continuous and/or stepped manner. | Chemistry | In the separation of different analytes based on their polarity. | 12 | 4 | 311c05f1-8a4a-4f8e-b257-f2b39e990419 | 2023 |
In the technique of normal phase liquid chromatography: | The stationary phase is polar and the mobile phase is non-polar. | The stationary phase has the same polarity as the mobile phase. | The stationary phase is less polar than the mobile phase. | Chemistry | The mobile phase is a pH-regulating solution. | 13 | 2 | 0bb8d1bb-6cd4-4205-b93b-c0e5cbb410e8 | 2023 |
What type of detectors are used in the ion chromatography technique with suppressor columns? | Spectrophotometric. | Amperometric. | Of flame ionization. | Chemistry | Of conductivity. | 14 | 3 | 7307a75d-8db5-4177-bd6d-bb5fa8ce94b2 | 2023 |
What is the elution order of solutes in size exclusion chromatography? | Decreasing molecular weight. | Increasing isoelectric point. | Increasing polarity. | Chemistry | Increasing molecular weight. | 15 | 2 | 90e265d6-3577-4108-962b-58537607e627 | 2023 |
The Kjeldahl method is used to measure the percentage of an element in a mixture. What element is it referring to? | Nitrogen. | Carbon. | Copper. | Chemistry | Iron. | 16 | 2 | 82d63e08-7ed5-4699-8cd8-1a9b3c96f519 | 2023 |
If we wish to measure the concentration of cortisol (steroid produced by the adrenal glands) in a teenager's urine through liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS), what substance is most suitable as an internal standard? | Deuterated cortisol. | Testosterone. | Albumin. | Chemistry | Cholesterol. | 17 | 2 | a2ce591c-c3b4-4504-a79d-61a6d0d5252c | 2023 |
Which of the following statements about electrospray ionization mass spectrometry (ESI/MS) is correct?: | In negative ion mass spectrometry, all voltages are positive, while for positive ions, negative voltages are used. | Non-volatile additives in the mobile phase (such as phosphate buffer) do not interfere with ionization and their use is recommended. | Electrospray can create new molecules, which did not exist in the previous aqueous solution. | Chemistry | The use of low ionic strength additives is recommended in order to allow the ionization and detection of the analyte ion. | 18 | 3 | cd36b85e-cf07-41f4-97e5-23b02e07a4cc | 2023 |
Which of the following statements regarding Beer's law is not true?: | Beer's law does not work well with diluted solutions (<0.01 M). | Beer's law applies to monochromatic radiation. | Beer's law states that absorbance is proportional to the concentration of the absorbing species. | Chemistry | Beer's law is complied with when the absorbing species does not participate in a concentration-dependent equilibrium. | 19 | 2 | f659c76f-c23f-4b39-8ea0-43308f51aa79 | 2023 |
In high performance liquid chromatography (HPLC), the use of a smaller particle as the stationary phase of the column implies: | Higher resistance to flow and therefore higher working pressure. | Greater theoretical plate height. | Broadening of the peaks. | Chemistry | Increase in the optimal time for chromatographic separation. | 20 | 2 | 10c0d564-4d02-4778-8a86-f1d5492148d8 | 2023 |
In column liquid chromatography, we refer to dead time as: | Time the solute is outside of the column packing. | Time that the solute spends absorbed within the column packing. | Time it takes for a substance not retained by the column to reach the detector. | Chemistry | Time it takes for a strongly retained substance to elute and reach the detector. | 21 | 4 | 031f5bc8-570d-4b14-b32f-55f093ec8b2d | 2023 |
Which of the following statements is NOT TRUE regarding a calibration procedure using the standard addition method? | The calibration curve should always be linear in the sample matrix. | It can be used to correct signal losses due to sample preparation. | It is compatible with the use of an internal standard. | Chemistry | The complex interference effects due to the matrix are compensated. | 22 | 1 | 89ad09b1-8917-4391-b59c-6fdedde5612e | 2023 |
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