Questions and Answers of Chemistry The Central Science

Disulfides are compounds that have S-S bonds, like peroxides have O-O bonds. Thiols are organic compounds that have the general formula R-SH, where R is a generic hydrocarbon. The SH- ion is the
Aqueous solutions of ammonia (NH3) and bleach (active ingredient NaOCl) are sold as cleaning fluids, but bottles of both of them warn: “Never mix ammonia and bleach, as toxic gases may be
Give the symbol for(a) A proton, (b) A beta particle, (c) A positron.
Which of the following statements best explains why alpha emission is relatively common, but proton emission is extremely rare?(a) Alpha particles are very stable because of magic numbers of protons
Which statement best explains why nuclear transmutations involving neutrons are generally easier to accomplish than those involving protons or alpha particles?(a) Neutrons are not a magic number
Which statement identifies which of these two compounds is more stable and explains why?(a) The carbon compound because C is less electronegative than Si(b) The silicon compound because Si forms
Write balanced equations for (a) 23892U(α, n)24194Pu, (b) 147N(α, p)178O,(c) 5626Fe(α, β-)6029Cu.
Which of the following statements are true?(a) Both nitrogen and phosphorus can form a pentafluoride compound.(b) Although CO is a well-known compound, SiO does not exist under ordinary
Which of the following statements are true?(a) Si can form an ion with six fluorine atoms, SiF62-, whereas carbon cannot.(b) Si can form three stable compounds containing two Si atoms each, Si2H2,
(a) Determine the charge of the aluminosilicate ion whose composition is AlSi3O10.(b) Using Figure 22.32, propose a reasonable description of the structure of this aluminosilicate.Figure 22.32
An Iron corrodes to produce rust, Fe2O3, but other corrosion products that can form are Fe(O)(OH), iron oxyhydroxide, and magnetite, Fe3O4. (a) What is the oxidation number of Fe in iron
Copper corrodes to cuprous oxide, Cu2O, or cupric oxide, CuO, depending on environmental conditions. (a) What is the oxidation state of copper in cuprous oxide? (b) What is the oxidation
A disproportionation reaction is an oxidation–reduction reaction in which the same substance is oxidized and reduced. Complete and balance the following disproportionation reactions:(a) Ni+(aq) →
The physical properties of D2O differ from those of H2O because(a) D has a different electron configuration than O.(b) D is radioactive.(c) D forms stronger bonds with O than H does.(d) D is much
When aluminum replaces up to half of the silicon atoms in SiO2, a mineral class called feldspars result. The feldspars are the most abundant rock-forming minerals, comprising about 50% of the
Write out the ground-state electron configurations of(a) Ti3+, (b) Ru2+, (c) Au3+, (d) Mn4+.
Which species are more likely to act as ligands? (a) Positively charged ions or negatively charged ions? (b) Neutral molecules that are polar or those that are nonpolar?
For each of the following molecules or polyatomic ions, draw the Lewis structure and indicate if it can act as a monodentate ligand, a bidentate ligand, or is unlikely to act as a ligand at all:(a)
For each of the following pairs, identify the molecule or ion that is more likely to act as a ligand in a metal complex:(a) Acetonitrile (CH3CN) or ammonium (NH4+),(b) Hydride (H-) or hydronium
If the lobes of a given d-orbital point directly at the ligands, will an electron in that orbital have a higher or lower energy than an electron in a d-orbital whose lobes do not point directly at
What is the DNA sequence for the molecule shown here? HO fo H₂C 0- -0-- Р H -O-P-O- NH₂ NH₂ HO N H NH₂
For a given metal ion and set of ligands, is the crystal-field splitting energy larger for a tetrahedral or an octahedral geometry?
The square-planar complex [Pt(en)Cl2] only forms in one of two possible geometric isomers. Which isomer is not observed: cis or trans?
For each of the following hydrocarbons, state how many carbon atoms are in each molecule:(a) Methane(b) Decane(c) 2-methylhexane(d) Neopentane(e) Acetylene
True or false: The weaker a single bond in a molecule, the greater the chance it will be the site of a reaction (compared to stronger single bonds in the molecule).
Is 3-chloro-3-methylhexane chiral?
Draw each molecule given its name and the following information.(a) Nitroglycerin, also known as 1,2,3-trinitroxypropane, the active ingredient in dynamite and a medication administered to people
You have samples of four compounds: dimethyl ether, methane, difluoromethane, and ethanol. You measure the boiling points of the compounds as -128 °C, -52 °C, -25 °C, and 78 °C, but then lose the
Shown here are sketches of two processes. Which of the processes refers to the ductility of metals and which refers to malleability of metals?(a)(b) Force Force
Which diagram best represents a liquid–liquid emulsion such as milk? The colored balls represent different liquid molecules.(a)(b)(c)
You are given a gray substance that melts at 700 °C; the solid is a conductor of electricity and is insoluble in water. Which type of solid (molecular, metallic, covalent-network, or ionic) might
You may have heard that “antioxidants” are good for your health. Is an “antioxidant” an oxidizing agent or a reducing agent?
Indicate whether each statement is true or false: (a) The cathode is the electrode at which oxidation takes place.(b) A galvanic cell is another name for a voltaic cell.(c) Electrons flow
Indicate whether each statement is true or false: (a) The anode is the electrode at which oxidation takes place. (b) A voltaic cell always has a positive emf. (c) A salt bridge or
A voltaic cell utilizes the following reaction:4Fe2+(aq) + O2(g) + 4 H+(aq) → 4Fe3+(aq) + 2H2O(l)(a) What is the emf of this cell under standard conditions?(b) What is the emf of this cell when
If you compare the solubilities of the noble gases in water, you find that solubility increases from smallest atomic weight to largest, Ar < Kr < Xe. Which of the following statements is the
An ionic compound has a very negative ΔHsoln in water. (a) Would you expect it to be very soluble or nearly insoluble in water? (b) Which term would you expect to be the largest negative
For each of these reactions, identify the acid and base among the reactants, and state if the acids and bases are Lewis, Arrhenius, and/or Brønsted–Lowry:(a) PCl4+ + Cl- → PCl5(b) NH3 + BF3 →
Which of the following statements is false?(a) An Arrhenius base increases the concentration of OH- in water.(b) A Brønsted-Lowry base is a proton acceptor.(c) Water can act as a Brønsted–Lowry
(a) The hydrogen sulfite ion (HSO3-) is amphiprotic. Write a balanced chemical equation showing how it acts as an acid toward water and another equation showing how it acts as a base toward water.(b)
The Earth’s oceans have a salinity of 35. What is the concentration of dissolved salts in seawater when expressed in ppm? What percentage of salts must be removed from seawater before it can be
What is the minimum number of atoms that could be contained in the unit cell of an element with a body-centered cubic lattice?(a) 1, (b) 2, (c) 3, (d) 4, (e) 5.
What is the minimum number of atoms that could be contained in the unit cell of an element with a face-centered cubic lattice?(a) 1, (b) 2, (c) 3, (d) 4, (e) 5.
Which two statements about gas mixtures are true?(a) Gases always mix with other gases because the gas particles are too far apart to feel significant intermolecular attractions or repulsions.(b)
A series of anions is shown below:The anion on the far right is called “BARF” by chemists, as its common abbreviation sounds similar to this word.(a) What is the central atom and the number of
The “free-base” form of cocaine (C17H21NO4) and its protonated hydrochloride form (C17H22ClNO4) are shown below; the free-base form can be converted to the hydrochloride form with one equivalent
The following table presents the solubilities of several gases in water at 25 °C under a total pressure of gas and water vapor of 1 atm. (a) What volume of CH4(g) under standard conditions of
KBr is relatively soluble in water, yet its enthalpy of solution is +19.8 kJ/mol. Which of the following statements provides the best explanation for this behavior?(a) Potassium salts are always
The solubility of MnSO4 . H2O in water at 20 °C is 70 g per 100 mL of water. (a) Is a 1.22 M solution of MnSO4 . H2O in water at 20 °C saturated, supersaturated, or unsaturated?(b) Given a
Indicate whether each statement is true or false:(a) The higher the temperature, the more soluble most gases are in water.(b) The higher the temperature, the more soluble most ionic solids are in
Indicate whether each statement is true or false:(a) If you compare the solubility of a gas in water at two different temperatures, you find the gas is more soluble at the lower temperature.(b) The
Ascorbic acid (vitamin C, C6H8O6) is a water-soluble vitamin. A solution containing 80.5 g of ascorbic acid dissolved in 210 g of water has a density of 1.22 g/mL at 55 °C. Calculate(a) The mass
Soaps consist of compounds such as sodium stearate, CH3(CH2)16COO-Na+ , that have both hydrophobic and hydrophilic parts. Consider the hydrocarbon part of sodium stearate to be the “tail” and the
The normal boiling point of ethanol, CH3CH2OH, is 78.4 °C. When 9.15 g of a soluble nonelectrolyte is dissolved in 100.0 g of ethanol at that temperature, the vapor pressure of the solution is 7.40
Carbon disulfide (CS2) boils at 46.30 °C and has a density of 1.261 g/mL. (a) When 0.250 mol of a non dissociating solute is dissolved in 400.0 mL of CS2, the solution boils at 47.46 °C. What is
Which of these statements about how the percent ionization of a weak acid depends on acid concentration is true?(a) Line A is most accurate because Ka does not depend on concentration.(b) Line A is
(a) What are the units usually used to express the rates of reactions occurring in solution? (b) As the temperature increases, does the reaction rate increase or decrease? (c) As a reaction
(a) Can an intermediate appear as a reactant in the first step of a reaction mechanism? (b) On a reaction energy profile diagram, is an intermediate represented as a peak or a valley? (c)
Write the expression for Kc for the following reactions. In each case indicate whether the reaction is homogeneous or heterogeneous.(a) 3NO(g) ⇌ N2O(g) + NO2(g)(b) CH4(g) + 2H2S(g) ⇌ CS2(g) +
Write the expressions for Kc for the following reactions. In each case indicate whether the reaction is homogeneous or heterogeneous.(a) 2O3(g) ⇌ 3O2(g)(b) Ti(s) + 2 Cl2(g) Δ TiCl4(l)(c) 2C2H4(g)
When the following reactions come to equilibrium, does the equilibrium mixture contain mostly reactants or mostly products?(a) N2(g) + O2(g) ⇌ 2NO(g) Kc = 1.5 x 10-10(b) 2SO2(g) + O2(g) ⇌ 2SO3(g)
(a) Is the dissociation of fluorine molecules into atomic fluorine, F2(g) ⇌ 2F(g) an exothermic or endothermic process?(b) If the temperature is raised by 100 K, does the equilibrium constant for
True or false: When the temperature of an exothermic reaction increases, the rate constant of the forward reaction decreases, which leads to a decrease in the equilibrium constant, Kc.
If Kc = 1 for the equilibrium 2 A(g) ⇌ B(g) , what is the relationship between [A] and [B] at equilibrium?
At a temperature of 700 K, the forward and reverse rate constants for the reaction 2 HI(g) ⇌ H2(g) + I2(g) are kf = 1.8 x 10-3 M-1 s-1 and kr = 0.063 M-1 s-1. (a) What is the value of
At 800 K, the equilibrium constant for the reaction A2(g) ⇌ 2A(g) is Kc = 3.1 x 10-4. (a) Assuming both forward and reverse reactions are elementary reactions, which rate constant do you
Predict how each molecule or ion would act, in the Brønsted- Lowry sense, in aqueous solution by writing “acid,” “base,” “both,” or “neither” on the line provided.(a) HCO3-, the
The following boxes represent aqueous solutions containing a weak acid, HA and its conjugate base, A-. Water molecules, hydronium ions, and cations are not shown. Which solution has the highest pH?
Predict the products of the following acid–base reactions, and predict whether the equilibrium lies to the left or to the right of the reaction arrow:(a) O2-(aq) + H2O(l) ⇌(b) CH3COOH(aq) +
A saturated solution of Cd(OH)2 is shown in the middle beaker. If hydrochloric acid solution is added, the solubility of Cd(OH)2 will increase, causing additional solid todissolve. Which of the two
(a) Write a chemical equation that illustrates the autoionization of water. (b) Write the expression for the ion product constant for water, Kw. (c) If a solution is described as basic,
The samples of nitric and acetic acids shown here are both titrated with a 0.100 M solution of NaOH(aq).Determine whether each of the following statements concerning these titrations is true or
Ephedrine, a central nervous system stimulant, is used in nasal sprays as a decongestant. This compound is a weak organic base:C10H15ON(aq) + H2O(l) ⇌ C10H15ONH+(aq) + OH-(aq)A 0.035 M solution of
Phenol, C6H5OH, has a Ka of 1.3 x 10-10.(a) Write out the Ka reaction for phenol.(b) Calculate Kb for phenol’s conjugate base.(c) Is phenol a stronger or weaker acid than water?
Ammonia, NH3, acts as an Arrhenius base, a Brønsted-Lowry base, and a Lewis base, in aqueous solution. Write out the reaction NH3 undergoes with water and explain what properties of ammonia
The fluoride ion reacts with water to produce HF.(a) Write out the chemical equation for this reaction.(b) Will a concentrated solution of NaF in water be acidic, basic, or neutral?(c) Is fluoride
Which, if any, of the following statements are true?(a) The stronger the base, the smaller the pKb.(b) The stronger the base, the larger the pKb.(c) The stronger the base, the smaller the Kb.(d) The
The pKb of water is _______.(a) 1 (b) 7 (c) 14 (d) Not defined(e) None of the above
At 50 °C, the ion-product constant for H2O has the value Kw = 5.48 x 10-14. (a) What is the pH of pure water at 50 °C? (b) Based on the change in Kw with temperature, predict whether ΔH
(a) If the molar solubility of CaF2 at 35°C i s 1.24 x 10-3 mol/L, what is Ksp at this temperature? (b) It is found that 1.1 x 10-2 g SrF2 dissolves per 100 mL of aqueous solution at 25°C.
Calculate the solubility of LaF3 in grams per liter in (a) Pure water, (b) 0.010 M KF solution, (c) 0.050 M LaCl3 solution.
The first stage of treatment at the reverse osmosis plant in Carlsbad, California, is to flow the water through rock, sand, and gravel as shown here. Would this step remove particulate matter? Would
A solution containing several metal ions is treated with dilute HCl; no precipitate forms. The pH is adjusted to about 1, and H2S is bubbled through. Again, no precipitate forms. The pH of the
Lead(II) carbonate, PbCO3, is one of the components of the passivating layer that forms inside lead pipes. (a) If the Ksp for PbCO3 is 7.4 x 10-14 what is the molarity of Pb2+ in a saturated
Salts containing the phosphate ion are added to municipal water supplies to prevent the corrosion of lead pipes. (a) Based on the pKa values for phosphoric acid (pKa1 = 7.5 x 10-3, pKa2 = 6.2 x
Calculate the solubility of Mg(OH)2 in 0.50 MNH4Cl.
The value of Ksp for Mg3(AsO4)2 is 2.1 x 10-20. The AsO43- ion is derived from the weak acid H3AsO4 (pKa1 = 2.22; pKa2 = 6.98; pKa3 = 11.50). (a) Calculate the molar solubility of Mg3(AsO4)2 in
Although there are many ions in seawater, the overall charges of the dissolved cations and anions must maintain charge neutrality. Consider only the six most abundant ions in seawater, as listed in
(a) How are the boundaries between the regions of the atmosphere determined? (b) Explain why the stratosphere, which is about 35 km thick, has a smaller total mass than the troposphere, which is
Consider the Earth’s energy balance shown in Figure 18.12.Figure 18.12(a) How many different sources transfer energy to the atmosphere? Which makes the largest contribution? What is the total
The dissociation energy of a carbon–bromine bond is typically about 276 kJ/mol. (a) What is the maximum wavelength of photons that can cause C-Br bond dissociation?(b) Which kind of
The wavelength at which the O2 molecule most strongly absorbs light is approximately 145 nm. (a) In which region of the electromagnetic spectrum does this light fall?(b) Would a photon whose
The ultraviolet spectrum can be divided into three regions based on wavelength: UV-A (315–400 nm), UV-B (280–315 nm), and UV-C (100–280 nm). (a) Photons from which region have the highest
The average bond enthalpies of the C-F and C-Cl bonds are 485 kJ/mol and 328 kJ/mol, respectively.(a) What is the maximum wavelength that a photon can possess and still have sufficient energy to
(a) When chlorine atoms react with atmospheric ozone, what are the products of the reaction? (b) Based on average bond enthalpies, would you expect a photon capable of dissociating a C-Cl bond
Nitrogen oxides like NO2 and NO are a significant source of acid rain. For each of these molecules write an equation that shows how an acid is formed from the reaction with water.
Predict the signs of ΔH and ΔS for this reaction. Explain your choice. $4
The atmosphere of Mars is 96% CO2, with a pressure of approximately 6 x 10−3 atm at the surface. Based on measurements taken over a period of several years by the Rover Environmental Monitoring
Phosphorus is present in seawater to the extent of 0.07 ppm by mass. Assuming that the phosphorus is present as dihydrogenphosphate, H2PO4-, calculate the corresponding molar concentration of H2PO4-
(a) The EPA threshold for acceptable levels of lead ions in water is <15 ppb. What is the molarity of an aqueous solution with a concentration of 15 ppb?(b) Concentrations of lead in the

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