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Which of the following statements is correct?:
The intramolecular aldol condensation of 2,5-hexanedione leads to a cyclic α,β-unsaturated carbonyl compound with 6 members.
The treatment of hexanedial with aqueous base results in 1-cyclopentenecarbaldehyde.
The Robinson annulation consists of two consecutive intramolecular aldol reactions.
Chemistry
Organolithiums give conjugate additions to α, β-unsaturated carbonyl compounds.
53
1
0eb5b2d0-2234-4f84-9b39-ba3dfe04cabc
2020
The reduction of a ketone to a methylene under basic conditions, by treatment with hydrazine and KOH at high temperature, is known as:
Reduction with hydrides.
Clemmensen Reduction.
McIntosh Reduction.
Chemistry
Wolff-Kishner Reduction.
54
3
4a9d2e02-879e-4b8a-a682-729fa86a09c3
2020
Indicate the correct IUPAC name for the compound with the following structure: (CH3)2CHCH2CHOHCH2CH3
5-methyl-3-hexanol.
2-methyl-4-hexanol.
1-isopropyl-2-hexanol.
Chemistry
1,4,4-trimethyl-2-butanol.
55
2
fa1bc92f-b473-4a56-aed7-287afe2d616a
2020
The treatment in a basic medium (alkoxide) of 2-methyl-1,3-cyclohexadione with methylvinylketone leads to:
8a-methyl-3,4,6,7,8,8a-hexahydronaphthalen-1-one.
4a-methyl-4,4a,5,6,7,8-hexahydronaphthalen-2-one.
8a-methyl-2,3,4,6,8,8a-hexahydronaphthalen-1,7-dione.
Chemistry
8a-methyl-3,4,8,8a-tetrahydronaphthalene-1,6- dione.
56
3
4c5f76f6-9e66-46df-8195-97dce6666fba
2020
When toluene undergoes an Electrophilic Aromatic Substitution, the methyl group is an activating group and furthermore:
Directs in ortho and para.
Orients in ortho.
Directs into meta.
Chemistry
Directs in meta and ortho.
57
2
54c0f48a-5254-4934-9029-5919800eba30
2020
In the presence of soluble palladium complexes, alkyl halides undergo a carbon-carbon bond formation reaction with alkenes to produce dienes. This process is known as:
Suzuki Reaction.
Heck Reaction.
Stille Reaction.
Chemistry
Sonogashira Reaction.
58
1
c68676e0-dad2-4b29-b2ba-1d4692ed801f
2020
The acid hydrolysis of esters and amides requires:
Stoichiometric quantities of acid, in both cases.
Catalytic amounts of acid, in both cases.
Catalytic quantities of acid for the amides and stoichiometric in the case of the esters.
Chemistry
Catalytic amounts of acid for the esters and stoichiometric in the case of amides.
59
3
4a81cbd1-d410-42e8-8777-b21fbf4e65a2
2020
The major product of the addition of water to propene in an acidic medium is:
1-propanol.
2-propanol.
1,2-dihydroxypropane.
Chemistry
Acetone.
60
1
164fbc85-f4c8-4e70-80d5-7cd2e41ed1b5
2020
Which of the following statements is true?:
The bromination of benzene requires a catalyst.
The 1,3-cyclobutadiene is an aromatic compound.
The halogens are deactivating and orient to meta in an electrophilic aromatic substitution reaction.
Chemistry
Aromatic electrophilic substitution is a concerted reaction.
61
2
3b87ba05-3617-49c8-88f1-7c967c45189e
2020
The indole cyclic system is reduced with lithium in liquid ammonia to mainly produce the following:
1,2-dihydroindole.
2,3-dihydroindole.
2,3-cis-indolines.
Chemistry
4,7-dihydroindole.
62
3
54d85ac0-1e02-4597-b844-84b6637f4b58
2020
In a three-step synthetic route, 1-bromo-2,2-dimethylpropane is treated with (1) magnesium; (2) formaldehyde; (3) aqueous solution of HCl. What organic product is expected to be obtained?
1-Chloro-2,2-dimethylpropane.
2,2-Dimethylpropane.
3,3-dimethyl-1-butanol.
Chemistry
2,2-Dimethyl-1-propanol.
63
4
0871a07a-9c7e-44c7-b90d-3ab4bbf5bfb7
2020
What organic product do you expect from the reaction between propanol and potassium dichromate in an acidic medium?
Propanal.
Propanoic acid.
Propane.
Chemistry
1,1-Propanediol.
64
1
c50b9469-bee8-4b10-9b4b-7efdb4feb964
2020
The oxidation state of the carbon atom in chloroform is:
+1.
-1.
-2.
Chemistry
+2.
65
3
ba5b79e8-0345-4c12-9d62-1816cfa204ed
2020
The strained ring of an epoxide opens due to the nucleophilic attack of amines to form:
β- amino alcohols.
α-amino alcohols.
1,3-diols.
Chemistry
α-azidoalcohols.
66
2
b9c11f58-3745-4eac-9827-80af3d63d95d
2020
What product will be formed in the reaction of 5-methyl-3-hexanone with (C6H5)3P=C(CH3)2?
2-ethyl-4-methyl-1-pentene.
3-ethyl-2,5-dimethyl-2-hexene.
2-ethyl-3,5-dimethyl-2-hexene.
Chemistry
2-isopropyl-4-methyl-1-pentene.
67
1
5f22b3d9-5ba8-470f-9c3c-0289e3f75698
2020
Furan reacts with bromine in methanol at 10ºC to form:
3-bromofuran.
2-bromofuran.
2-methoxyfuran.
Chemistry
2,5-dimethoxy-2,5-dihydrofuran.
68
3
4d81ad75-da66-45cd-8861-fa9727ca17f0
2020
What reagents should we use for the preparation of 3-methyl-3-hexanol?
3-hexanone and methylmagnesium bromide.
Butanone and ethylmagnesium bromide.
3-pentanone and propylmagnesium bromide.
Chemistry
2-pentanone and methylmagnesium bromide.
69
2
7ec18dc7-c1fc-4c7f-a964-1f62bb0a5d0f
2020
The reaction product of acetyl chloride with methoxide is:
Acetic acid.
Acetate.
Methyl acetate.
Chemistry
Acetone.
70
4
3ac10ac4-8a4a-4749-95ba-a78f3f4dd173
2020
Immunoglobulins or antibodies:
These are soluble proteins that form the protein base of the immune response.
These are soluble proteins that constitute the protein basis of the hormonal response.
One of the most important is Hemoglobin.
Chemistry
They are small, globular and soluble proteins.
71
2
e2417a47-7164-427c-a545-e75f4a208371
2020
Which of the following statements is true for the protein kinase activated by AMP (AMPK)?:
It is activated with a low AMP: ATP ratio.
It activates when the energy charge of the cells is low.
Phosphorylates substrates to inhibit glucose uptake.
Chemistry
Activates pathways such as the synthesis of fatty acids, triacylglycerols and cholesterol.
72
1
ec472c4e-751b-4354-b9ab-97f429b41e5a
2020
Phenylketonuria, the most common cause of elevated phenylalanine in plasma, is caused by a defect in the activity of the enzyme:
Arginase.
Cystathionine beta-synthase.
Tyrosine aminotransferase.
Chemistry
Phenylalanine hydroxylase.
73
3
71c311e8-26f9-4436-8e6b-9e8a7fc24da1
2020
What type of lipoproteins is the reverse transport of cholesterol associated with?
LDL.
HDL.
Chylomicrons.
Chemistry
VLDL:
74
1
79d5431f-57e5-4621-b1de-05e95b5f7685
2020
The mitochondrial DNA molecule is:
Circular, double-stranded.
Circular, single-stranded.
Linear, double chain.
Chemistry
Linear, single chain.
75
2
ee369277-7233-4584-850d-7a88e0380803
2020
In a conjugated protein, the prosthetic group:
It is a different subunit from the others.
It is a globular region.
It is bonded by hydrogen bridges.
Chemistry
It is a part of the protein that is not composed of amino acids.
76
3
b4e4c98a-77e3-43bf-b99d-db09adb2d3de
2020
The regulatory enzyme of cholesterol biosynthesis is:
Thiolase.
Cholesterol esterase.
3-Hydroxy 3-methylglutaryl-CoA reductase.
Chemistry
Phospholipase C.
77
4
022da853-5430-4eb3-9ac6-9822fe43d374
2020
What characterizes the lactate dehydrogenase enzyme in lactic fermentation?:
Consume NADH.
Release CO2.
Allow the aerobic glycolysis to continue.
Chemistry
Having acetyl CoA as a substrate.
78
2
6e10931b-456d-4275-a9ca-ded56c8b360f
2020
Which of the following enzymes has the in vivo function of catalyzing the replication of mitochondrial DNA in eukaryotic cells?:
DNA polymerase β.
DNA polymerase α.
DNA polymerase δ. H3C Cl O + CH3O -
Chemistry
DNA polymerase γ.
79
3
0f3cbc5a-a3f8-4746-a955-d231b8998653
2020
Which of these statements about the secondary structure of proteins in alpha helix is correct?:
It can be parallel or antiparallel.
Each turn of the helix contains 3.6 amino acid residues.
In this secondary structure, the side chains of the amino acids are directed towards its interior.
Chemistry
It can accommodate any type of amino acid with the same probability.
80
1
5cd408eb-c4b8-4272-8afa-fe3820ec4f29
2020
Which of the following statements about ketone bodies is true?:
In untreated diabetes, its production is inhibited.
They are produced in the muscle and are used in the liver.
The brain uses them as fuel during long fasting periods.
Chemistry
Its production increases after ingestion in healthy individuals.
81
4
0284e5db-1a25-4f9b-b82d-6da739ea6e47
2020
The isoelectric point or isoelectric pH (pl) of an amino acid is the characteristic pH at which:
Its net charge is negative.
It has a net positive charge.
It is more hydrophobic.
Chemistry
The net charge is zero.
82
3
50f86ab4-ba4a-46dd-8d21-0b3f9b02333c
2020
High concentrations of citrate reduce the activity of:
Glycolysis.
The pentose phosphate pathway.
The synthesis of fatty acids.
Chemistry
Gluconeogenesis.
83
2
2f43d0d8-eab4-4e6c-bfb7-e690646bb796
2020
Which of the following nutrients is a precursor of a cofactor that transports groups of one carbon with different oxidation states?:
Folic Acid.
Methionine.
Biotin.
Chemistry
Thiamine.
86
2
8b604849-c634-4aec-a0fa-4045a81a47b2
2020
In Lesch-Nyhan syndrome, the defect in the activity of the enzyme hypoxanthine-guanine phosphoribosyltransferase leads to the accumulation of:
Urea.
Uric Acid.
Cytidine.
Chemistry
Tetrahydrofolate.
87
1
a9652634-9824-4a92-a1f0-50e572690c97
2020
Muscle glycogenolysis does not directly contribute glucose to the blood because the muscle lacks the enzyme:
Phosphoglucomutase.
Phosphorylase.
Phosphoglucoisomerase.
Chemistry
Glucose-6-phosphatase.
88
3
275e82a8-0360-497f-9433-6f20728c32b5
2020
The tertiary structure of a polypeptide describes:
All aspects of the two-dimensional folding of the polypeptide.
The complete three-dimensional structure of the polypeptide chain.
The structural relationship between the subunits of a protein.
Chemistry
The number and location of disulfide bridges present in a polypeptide.
90
1
a0cc3912-4fa7-4540-8120-6c606dee0b25
2020
Regarding hemoglobin:
The intracellular pH does not influence the binding of O2.
Its O2 dissociation curve is hyperbolic.
Hemoglobin S is the form present in the Caucasian race.
Chemistry
The 2,3-bisphosphoglycerate reduces its affinity for O2.
91
3
121de7a3-e0d5-40a3-902f-ca97b4187ed4
2020
The percentage of Adenine (A) in the DNA of a bacterial chromosome is 22%; this implies that the percentages of Guanine (G), Thymine (T) and Cytosine (C) are:
G= 28%; T = 28%; C = 22%.
G = 30%; T = 22%; C = 26%.
G = 28%; T = 22%; C = 28%.
Chemistry
G = 22%; T = 28%; C = 28%.
92
4
1cc4de97-1b99-457c-94cf-185a56ab697e
2020
The thermal denaturation of DNA leads to:
The breaking of glycosidic bonds giving a hyperchromic effect.
A hypochromic effect.
The breaking of phosphodiester bonds giving a hyperchromic effect.
Chemistry
A melting temperature that depends on the content of bases.
93
3
30596ae4-5db0-4982-b312-650109511415
2020
In DNA replication in E. coli, indicate the correct answer:
The primers of DNA polymerase are called Okazaki fragments.
The primase enzyme catalyzes the synthesis of the DNA polymerase primers.
The DNA gyrase introduces positive helical supercoiling.
Chemistry
The removal of the primers is carried out by DNA polymerase III.
94
1
a3a9a46c-506a-48d8-99c9-7158f8952303
2020
The Sanger method for DNA sequencing requires the use of:
Ribonucleotides.
Dideoxynucleotides.
Nucleosides.
Chemistry
Deoxynucleotides.
95
1
72fbea52-9b81-4593-a354-dcb9b240eefa
2020
What is a plasmid?:
It is a very small DNA molecule that contains a single gene.
It is a virus that infects bacteria.
It is an enzyme that acts in the mechanisms of DNA repair.
Chemistry
It is a circular extrachromosomal DNA molecule.
96
3
adaea8b1-1610-4314-a0ce-e6a093a46f20
2020
Which of these statements related to the chemiosmotic theory, which links mitochondrial electron transport and oxidative phosphorylation, is correct?:
The energy released by electron transport is preserved as a transmembrane pH gradient.
The ATP synthase is not affected by the proton gradient.
Regardless of the entry point of the electrons in the transport chain, the number of ATP molecules synthesized is constant.
Chemistry
Oxidative phosphorylation can take place in a membrane-free system.
97
2
32b5e7c4-1302-496d-91b7-c46560d9e0e6
2020
Which of the following is not a vector capable of introducing genetic material into susceptible host cells?:
Virus.
Cosmid.
Operon.
Chemistry
Phage.
98
4
e6255151-a393-469d-ad98-edb349689954
2020
The fructose 2,6-bisphosphate:
It inhibits the activity of phosphofructokinase-1, thus inhibiting glycolysis.
Promotes the activity of fructose 1,6-bisphosphatase by promoting glycolysis.
It plays a major role in the regulation of both glycolysis and gluconeogenesis.
Chemistry
It plays a main role in the regulation of glycolysis, but not in gluconeogenesis.
99
4
18199fe6-a7dd-41b0-8edf-fd032a67e7fa
2020
Which enzyme is inhibited by malonyl-CoA to prevent the oxidation of fatty acids simultaneously to their biosynthesis?
The acyl-CoA dehydrogenase.
Carnitine acyltransferase I.
Thiolase.
Chemistry
The enoyl-CoA hydratase.
100
1
088e9970-1d34-4a51-9c84-1f8ccfd4af7b
2020
Gluconeogenesis is a metabolic pathway that:
It uses exactly the same enzymes as glycolysis, but acting in the opposite direction.
Leads to the mitochondrial synthesis of glucose from acetyl-CoA in mammals.
It is of a catabolic nature, although it generates less amount of ATP than the citric acid cycle.
Chemistry
It consumes a considerably larger amount of metabolic energy than that generated by glycolysis.
101
3
ca0eb126-1b1a-49c2-a550-c5eac1433a73
2020
What type of enzymatic inhibitor INCREASES Km and does not vary Vmax?
Competitive reversible inhibitor.
Non-competitive reversible inhibitor.
Irreversible inhibitor.
Chemistry
Reversible non-competitive inhibitor.
102
2
c9fd9c82-00f8-4db5-a162-6c26a1fea1af
2020
The carbonic anhydrase:
It catalyzes the conversion of carbonic acid into CO2 and water.
It is an extracellular enzyme.
It catalyzes the conversion reaction of H2CO3 into HCO3- and H+.
Chemistry
It has a very low replacement number.
103
2
4b6c06a0-9452-4aee-a343-680bd0b40558
2020
Regarding eukaryotic RNA polymerases, which of these statements is incorrect?:
The RNApol II transcribes the precursors of the mRNA.
The RNApol I transcribes the precursors of most rRNA.
The RNApol IV transcribes the precursors of the snRNA and the 5S rRNA.
Chemistry
The RNApol III transcribes the precursors of the tRNA.
104
4
7b1d06f4-cac4-4c85-860f-fd64cf9312e4
2020
The enzymes called proteases:
They catalyze the hydrolytic breakdown of peptide bonds in proteins.
They hydrolyze glycosidic bonds in proteins.
They hydrolyze phosphoester bonds in proteins.
Chemistry
They catalyze the hydrolytic cleavage of disulfide bonds in proteins.
105
2
d2e3091d-bf13-4d90-8306-fe051e553538
2020
What is the coordination number of an atom in a metal that has a compact hexagonal structure?
6.
4.
12.
Chemistry
8.
106
4
06eae316-f554-4f3e-baf8-1509818842a9
2020
What is the crystal structure of hydrogen fluoride?
The structure of blende.
The structure of sodium chloride.
Isolated molecules.
Chemistry
A zigzag structure.
107
3
1afb0d0d-3bfe-4ad8-a47b-3aac6b6d809f
2020
What is a ferroelectric material?:
Conductive material that can exhibit polarization in the absence of an electric field.
Conductive material that can exhibit polarization in the presence of an electric field.
Dielectric material that can exhibit polarization in the absence of an electric field.
Chemistry
Dielectric material that can exhibit polarization in the presence of an electric field.
108
4
15a5c3c1-7cbe-439f-a0e5-a7b72e0f3f8d
2020
What gas is released when slightly damp toluene is dried with calcium hydride?
Hydrogen.
Oxygen.
None.
Chemistry
Water.
109
2
ac4a8096-c23a-48d1-bbd3-c938b09757e6
2020
Of the following mixed transition metal oxides with spinel structure, which one has an inverse spinel structure?:
Co3O4.
FeCr2O4.
Mn3O4.
Chemistry
Fe3O4.
110
3
7e42f3b3-2710-47e8-8fe9-93df20bea3ca
2020
What do the electronic configurations of the ions O2- and O22-, according to the Molecular Orbital Theory, indicate?
The O22- species is paramagnetic while O2- is diamagnetic.
Both species have the same bond distance.
The bond order of O2- is higher than that of O22-.
Chemistry
The bond distance in O22- is smaller than in O2-.
111
4
50aab8ea-eb24-4c0b-bae6-5e43c962f7a6
2020
Which of the following statements about metallic packing is true?:
In the simple cubic packing, the coordination number of each atom is 8.
Body-centered cubic packing is the most compact.
All types of packing show the same kind of "holes".
Chemistry
Metals with hexagonal close packing and cubic close packing present the same percentage of space occupation and the same coordination number of all the metallic atoms.
112
3
4bd4796e-7eb5-4b80-ac4e-50e7f7345b64
2020
Which of the following species is not considered a pseudohalide?:
CN-.
C22-.
SCN-.
Chemistry
NCO-.
113
1
a2338670-82cf-40f4-9203-9a3f06011a5e
2020
Which species of mercury, with significant environmental presence, is considered the most toxic?
Methylmercury.
Dichloride of dimercure.
Liquid mercury.
Chemistry
Mercury vapor.
114
2
2b376232-0c65-41bc-abfb-f9558f001de2
2020
What is a hard magnetic material?
Ferrimagnetic or ferromagnetic material that presents low values of coercive field and remanence.
Ferrimagnetic or ferromagnetic material that has low coercive field values and high remanence values.
Ferrimagnetic or ferromagnetic material that presents high values of coercive field and low values of remanence.
Chemistry
Ferrimagnetic or ferromagnetic material that presents high values of coercive field and remanence.
115
3
a8212d15-770b-43d9-8b5e-45247ecf8aef
2020
What is the conduction band in electrical insulators and semiconductors?
It is the highest electronic energy band that is filled with electrons at 0 K.
It is the highest electronic energy band that is devoid of electrons at 0 K.
It is the lowest electronic energy band that is empty of electrons at 0 K.
Chemistry
It is the lowest electronic energy band that is filled with electrons at 0 K.
116
4
3f76e52c-5c56-4467-a72f-fe4b0e8bbc7b
2020
The sterling silver used in jewelry is:
An intermetallic compound.
A hard product.
An interstitial alloy.
Chemistry
A substitution alloy.
117
3
b002b175-7c95-449e-9397-759aec5ae6fd
2020
Which of these symmetry elements can a chiral molecule exhibit?:
Own axis of rotation.
Investment center.
Improper rotation axis.
Chemistry
Symmetry plane.
118
2
1aa1077e-fe70-46c3-af7e-9670cfa0e29b
2020
What is known as fatigue of a material?
Failure at relatively high levels of tension, of structures subjected to continuous tensions.
Failure at relatively high levels of tension, of structures subjected to fluctuating and cyclic tensions.
Failure at relatively low stress levels, of structures subjected to continuous stresses.
Chemistry
Failure at relatively low stress levels, of structures subjected to fluctuating and cyclic stresses.
119
3
fea622c2-9f37-4b29-a5f2-f926dfa8876d
2020
What shape does the XeF2 molecule present?
Angular, with an angle slightly less than 180º.
Linear.
Angular derivative of tetrahedron, with an angle close to 109º.
Chemistry
Angular derivative of equilateral triangle, with angle close to 120º.
120
1
cf804dcf-0c29-44ab-a110-daa1b6f9b1ad
2020
What are Pt(II) complexes usually like?
Octahedral and paramagnetic.
Octahedral and diamagnetic.
Square planar and paramagnetic.
Chemistry
Square planar and diamagnetic.
121
3
7346a877-2a00-40bb-b496-0f7acf4068aa
2020
The necessary operations for the industrial extraction of SO3 from SO2 and air are due to the fact that the reaction of SO2 with oxygen is:
Exothermic.
Endothermic.
Irreversible.
Chemistry
Fast enough at room temperature.
122
2
e3bd2e6d-29c5-4cab-999f-2d6851417274
2020
Which of the following metals is part of anticancer therapeutic agents?:
Lead.
Cadmium.
Strontium.
Chemistry
Beryllium.
123
4
fbbda071-931f-42ce-9075-ef80d55e4986
2020
The sodium dihydrogen phosphate, used in laxative drugs, is a substance:
Reducing.
Oxidizing agent.
Of alkaline (basic) nature.
Chemistry
Of acidic nature.
124
3
6066bad3-d66e-4751-b57c-006be147e38d
2020
What is the reaction order in radioactive decays, which is the basis for dating ancient objects through the 14C test, and rocks through U/Pb and Ar/K datings, and many other applications?
Of first order.
Of zero order.
Of fractional order.
Chemistry
Of order two.
125
2
a77860d9-b767-471d-b23d-21209c25cdc7
2020
Which of the following oxoacids, HCIO2, HBrO, HCIO4, HCIO, is the strongest?
HBrO.
HCIO2.
HCIO.
Chemistry
HCIO4.
126
3
af73a3e4-c918-4d75-ad86-a84c56e191b7
2020
What is the name of the type of configuration of a polymer in which the side groups are randomly placed on one side or the other of the main chain?
Sindiotactic.
Isotactic.
Pertactic.
Chemistry
Atactic.
129
3
66a15d49-eb7c-4f2c-8cc7-54bfe27b85de
2020
Which of the following oxides is considered amphoteric?:
Al2O3.
CO2.
B2O3.
Chemistry
MgO.
130
2
a68c66f7-be3c-4c68-9e35-e80d894f5834
2020
Phosphine (PH3) is a poisonous gas that:
It is somewhat soluble in water, yielding basic solutions.
It has an oxidizing nature.
It has a phosphorescent yellow color.
Chemistry
It is somewhat soluble in water, giving neutral solutions.
131
3
846b6978-33d0-4e7c-b423-d02a179317e6
2020
Why is silver chloride practically insoluble in water, but soluble in an ammonia solution?
Because ammonium chloride is formed and the pH decreases.
Why the pH increases.
Because ammonia coordinates with silver, and those complexes are soluble.
Chemistry
Because when basifying, chlorocomplexes of silver are formed that shift the equilibrium.
132
4
4a899fa6-ddd6-49e7-a773-f8f6331470ae
2020
Which of the following statements about Ellingham diagrams is correct?:
They represent the variation of the standard enthalpy of formation of the metallic oxides as a function of temperature.
They are useful for the study of chemical reactions in an aqueous medium.
The slope of all the lines represented remains constant as the temperature varies.
Chemistry
All the curves that are present have positive slopes except for CO2 (zero slope) and CO (negative slope).
133
3
af83bbfa-dbe4-4262-ac12-6303529824bb
2020
Why does radon cause significant environmental concern?:
It is a radioactive gas, which also disintegrates, producing other radioactive elements.
It reacts with hemoglobin, rendering it useless, preventing respiration.
It binds to the active sites of various enzymes in the body, preventing their function.
Chemistry
After inhaling it, it is not eliminated, and is toxic due to accumulation.
134
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The BF3 molecule:
It is pyramidal.
It cannot be represented by Lewis structures because it has unpaired electrons.
Contains double bonds.
Chemistry
It presents sp2 hybridization of the central B atom.
135
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Which of the following elements belongs to the main groups?:
Sm.
Eu.
Og.
Chemistry
It is.
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0cd4e4a1-c9f2-4d96-bbe5-80bef202a76e
2020
Why don't aluminum objects exposed to air corrode?:
Because they are coated with plastic.
Because they are coated with a layer of paint.
Because aluminum is not attacked by air at room temperature.
Chemistry
Because when aluminum comes into contact with oxygen, water, and the carbonic acid in the air, it gets covered by a layer of oxide which prevents further attack.
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What can be stated if nitric acid and sulfuric acid are compared?
In pure state, both are oily liquids at room temperature.
The oxidizing strength of nitric acid is lower than that of sulfuric acid.
Both are strong dehydrating agents.
Chemistry
In its pure state, nitric acid is a much better conductor of electricity than sulfuric acid due to its autoionization reactions.
138
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Which of the following statements is correct?:
Silicon doped with arsenic is an extrinsic p-type semiconductor.
Germanium is an insulator.
The conductivity of a metallic conductor and a semiconductor vary in the same way with the increase in temperature.
Chemistry
The conductivity of a metallic conductor decreases with the increase in temperature.
139
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fc12c4ad-2401-41c1-b6e1-858b789616fd
2020
What is the following law known as: "If two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in a simple ratio of whole numbers"?
Dalton's Law of Multiple Proportions.
Proust's Law of Definite Proportions.
Law of conservation of mass.
Chemistry
Richter's law or law of reciprocal proportions.
140
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2020
For the reaction: 2 A + B → C + D. It has been determined that its reaction rate is second order with respect to A and zero order with respect to B. At a certain temperature, the reaction rate is 0.048 M s -1, when the concentration of A is 0.63 M. If, at the same temperature, you want to triple the reaction rate, the concentration of A should be:
[3 x (0.63) ½ ] M.
(0.63 x 3) M.
[(0.63 x 3) ½ ] M.
Chemistry
[0.63 x 3 ½ ] M.
141
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What is the condition that an ideal solution must meet?
The solute and the solvent obey Henry's law.
The solute and the solvent obey Raoult's law.
The solute obeys Raoult's law.
Chemistry
The solvent follows Henry's Law.
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In consecutive first-order reactions of the type A → B → C, the concentration of the intermediate B:
Increases linearly with time.
It can be considered equal to zero.
It increases over time until it reaches a maximum and then decreases.
Chemistry
It remains constant over time.
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In a first order chemical reaction, the half-life of a reactant (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
Regardless of the initial concentration of the reactant.
145
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132f8549-8740-4459-8f83-5df12aa8af4d
2020
For which chemical species can the Schrödinger equation be solved exactly or analytically?
For any monoatomic ion with a single positive charge.
For molecules with a maximum of two nuclei.
For atoms or ions with a single electron.
Chemistry
For the atoms of hydrogen and helium.
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Is there any connection between the molecular description of a system and its thermodynamic properties?
Yes, statistical mechanics allows us to deduce expressions for the molecular and canonical partition functions and, from them, obtain thermodynamic properties.
No, the molecular description is based on quantum mechanics and thermodynamic properties are macroscopic observables.
Yes, knowing the value of any thermodynamic property, the distribution of molecules in the various microstates compatible with their total energy can be deduced.
Chemistry
Yes, the Boltzmann distribution function is the direct bridge between the molecular description and thermodynamic properties.
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For a thermodynamic process that takes place under constant volume conditions and where no work other than expansion is possible, it holds true that:
The variation of internal energy is greater than the heat flow at constant volume.
The variation of internal energy is equal to the heat flow at constant volume.
The change in enthalpy is equal to the heat flow at constant volume.
Chemistry
The variation of enthalpy is equal to the heat flow at constant pressure.
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For a given reaction, the standard enthalpy change is 15 kJ mol-1 and its activation enthalpy is 70 kJ mol-1. When introducing a catalyst, the activation enthalpy drops to 40 kJ mol-1. The value of the standard enthalpy change for the catalyzed reaction will be:
25 kJ per mol.
30 kJ per mole.
-15 kJ per mole.
Chemistry
15 kJ per mole.
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The critical temperature in a phase diagram for a pure substance is:
The temperature at which the sublimation curve ends.
The temperature at which the triple point of the substance occurs.
The temperature above which the gas cannot be liquefied by increasing the pressure.
Chemistry
The temperature at which solid, liquid, and gaseous states coexist in equilibrium.
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When a metal is exposed to electromagnetic radiation, the emission of electrons can 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 relative to 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.
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The chemical reaction: A(g) ↔ 2 B (g) is in equilibrium, if:
2µA = µB.
μA = μB.
μA + 2μB = 0.
Chemistry
μA = 2μB.
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2020
Which statement is correct in relation to the behavior of electrolytes in solution?:
Benzene is a weak electrolyte that partially dissociates in water.
The Ostwald dilution law can be used to determine the molar conductivity at infinite dilution for a weak acid.
Strong acids and bases have a degree of dissociation less than 50% when dissolved in water.
Chemistry
Salts are not electrolytes since they do not conduct electric current in solid state.
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Given that the normal boiling point of water is higher than the normal boiling point of ethanol, it can be deduced that:
The vapor pressure of water at a given temperature is lower than the vapor pressure of ethanol at the same temperature.
Water is more volatile than ethanol.
The strength of the intermolecular interactions of water is less than that of ethanol.
Chemistry
The vapor pressure of water at a given temperature is higher than the vapor pressure of ethanol at that same temperature.
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What does it mean that the wave function describing the state of a system is normalized?
That the function is finite.
That the function is continuous.
That the function is homogeneous.
Chemistry
The probability of finding the particle throughout all the space where it is defined should be one.
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2020
The best way to estimate the relative strength of hydrogen bonds between the molecules of halogen hydrides, H-X, is by measuring:
Molecular polarities.
The enthalpies of formation.
The enthalpies of vaporization.
Chemistry
The H-X bond energies.
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The ionization potential of the hydrogen atom coincides with the limit of the series of:
Lyman.
Paschen.
Pfund.
Chemistry
Balmer.
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The Stokes-Einstein equation allows us to relate:
The diffusion coefficient with the experimental speed constant.
The diffusion coefficient with the activation energy.
The steric factor and the collision frequency.
Chemistry
The diffusion coefficient with the solvent viscosity.
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