Questions and Answers of Chemistry The Central Science

Imagine that you have a metal bar sitting half in the Sun and half in the dark. On a sunny day, the part of the metal that has been sitting in the Sun feels hot. If you touch the part of the metal
Which of the following statements does not follow from the fact that the alkali metals have relatively weak metal–metal bonding?(a) The alkali metals are less dense than other metals.(b) The alkali
(a) What is a monomer?(b) Which of these molecules can be used as a monomer: benzene, ethene (also called ethylene), methane?
State whether each of these numbers is a reasonable value for a polymer’s molecular weight: 100 amu, 10,000 amu, 100,000 amu, 1,000,000 amu?
Indicate whether the following statement is true or false: For an addition polymerization, there are no by-products of the reaction (assuming 100% yield).
(a) What molecular features make a polymer flexible?(b) If you cross-link a polymer, is it more flexible or less flexible than it was before?
If you want to make a polymer for plastic wrap, should you strive to make a polymer that has a high or low degree of crystallinity?
Indicate whether each statement is true or false:(a) Elastomers are rubbery solids.(b) Thermosets cannot be reshaped.(c) Thermoplastic polymers can be recycled.
Which statement correctly describes a difference between graphene and graphite?(a) Graphene is a molecule but graphite is not.(b) Graphene is a single sheet of carbon atoms and graphite contains
What evidence supports the notion that buckyballs are actual molecules and not extended materials?(a) Buckyballs are made of carbon.(b) Buckyballs have a well-defined atomic structure and molecular
The electrical conductivity of aluminum is approximately 109 times greater than that of its neighbor in the periodic table, silicon. Aluminum has a face-centered cubic structure, and silicon has the
When you shine light of band gap energy or higher on a semiconductor and promote electrons from the valence band to the conduction band, do you expect the conductivity of the semiconductor to(a)
Look up the diameter of a silicon atom, in Å. The latest semiconductor chips have fabricated lines as small as 22 nm. How many silicon atoms does this correspond to?
Consider two ionic solids, both composed of singly-charged ions, that have different lattice energies.(a) Will the solids have the same solubility in water?(b) If not, which solid will be more
Are gases always miscible with each other? Explain
You take a sample of water that is at room temperature and in contact with air and put it under a vacuum. Right away, you see bubbles leave the water, but after a little while, the bubbles stop. As
Indicate whether each statement is true or false:(a) A solute will dissolve in a solvent if solute–solute interactions are stronger than solute-solvent interactions.(b) In making a solution, the
Indicate whether each statement is true or false:(a) NaCl dissolves in water but not in benzene (C6H6) because benzene is denser than water.(b) NaCl dissolves in water but not in benzene because
Two nonpolar organic liquids, hexane (C6H14) and heptane (C7H16), are mixed.(a) Do you expect ΔHsoln to be a large positive number, a large negative number, or close to zero? Explain.(b) Hexane and
For the dissolution of LiCl in water, ΔHsoln = -37 kJ/mol. Which term would you expect to be the largest negative number: ΔHsolvent, ΔHsolute, or ΔHmix?
Consider water and glycerol, CH2(OH)CH(OH)CH2OH.(a) Would you expect them to be miscible in all proportions? Explain.(b) List the intermolecular attractions that occur between a water molecule and a
Oil and water are immiscible. Which is the most likely reason?(a) Oil molecules are denser than water.(b) Oil molecules are composed mostly of carbon and hydrogen.(c) Oil molecules have higher molar
You make a solution of a nonvolatile solute with a liquid solvent. Indicate whether each of the following statements is true or false.(a) The freezing point of the solution is higher than that of the
You make a solution of a nonvolatile solute with a liquid solvent. Indicate if each of the following statements is true or false.(a) The freezing point of the solution is unchanged by addition of the
In the 1850’s, Michael Faraday prepared ruby-red colloids of gold nanoparticles in water that are still stable today. These brightly colored colloids look like solutions. What experiment(s) could
Choose the best answer: A colloidal dispersion of one liquid in another is called(a) A gel(b) An emulsion(c) A foam(d) An aerosol.
An “emulsifying agent” is a compound that helps stabilize a hydrophobic colloid in a hydrophilic solvent (or a hydrophilic colloid in a hydrophobic solvent). Which of the following choices is the
Aerosols are important components of the atmosphere. Does the presence of aerosols in the atmosphere increase or decrease the amount of sunlight that arrives at the Earth’s surface, compared to an
Proteins can be precipitated out of aqueous solution by the addition of an electrolyte; this process is called “salting out” the protein.(a) Do you think that all proteins would be precipitated
Compounds like sodium stearate, called “surfactants” in general, can form structures known as micelles in water, once the solution concentration reaches the value known as the critical micelle
An automotive fuel injector dispenses a fine spray of gasoline into the automobile cylinder, as shown in the bottom drawing here. When an injector gets clogged, as shown in the top drawing, the spray
Which of the following linear plots do you expect for a reaction A→products if the kinetics are(a) Zero order(b) First order(c) Second order? (i) (ii) Time Time (iii) (iv) Time Time (v) (vi) Time
The accompanying graph shows plots of ln k versus 1/T for two different reactions. The plots have been extrapolated to the y-intercepts. Which reaction (red or blue) has(a) The larger value for Ea(b)
The reaction 2NO(g) + Cl2(g) → 2NOCl(g) was performed and the following data obtained under conditions of constant [Cl2]:(a) Is the following mechanism consistent with the data?NO(g) + Cl2 (g) →
In Figure 14.22, we saw that Br - (aq) catalyzes the decomposition of H2O2(aq) into H2O(l) and O2(g). Suppose that some KBr(s) is added to an aqueous solution of hydrogen peroxide. Make a sketch
Consider the reaction A + B → C + D. Is each of the following statements true or false?(a) The rate law for the reaction must be Rate = k[A][B].(b) If the reaction is an elementary reaction, the
The following kinetic data are collected for the initial rates of a reaction 2X + Z → products:(a) What is the rate law for this reaction?(b) What is the value of the rate constant with proper
A first-order reaction A → B has the rate constant k = 3.2 × 10-3 s-1. If the initial concentration of A is 2.5 × 10-2 M, what is the rate of the reaction at t = 660 s?
At 28 °C, raw milk sours in 4.0 h but takes 48 h to sour in a refrigerator at 5°C. Estimate the activation energy in kJ/mol for the reaction that leads to the souring of milk?
At 1000 K, Kp = 1.85 for the reactionSO2(g) + 1/2O2(g) ⇌ SO3(g)(a) What is the value of Kp for the reaction SO3(g) ⇋ SO2(g) + 1/2O2(g)?(b) What is the value of Kp for the reaction 2SO2(g) + O2(g)
The following equilibria were attained at 823 K:CoO(s) + H2(g) ⇌ Co(s) + H2O(g) Kc = 67CoO(s) + CO(g) ⇌ Co(s) + CO2(g) Kc = 490Based on these equilibria, calculate the equilibrium
Consider the equilibriumN2(g) + O2(g) + Br2(g) ⇌ 2NOBr(g) Calculate the equilibrium constant Kp for this reaction, given the following information (at 298 K):2NO(g) + Br2(g)
Consider the following equilibrium:2H2(g) + S2(g) ⇋ 2H2S(g)Kc = 1.08 Χ 107at 700 °C(a) Calculate Kp.(b) Does the equilibrium mixture contain mostly H2 and S2 or mostly H2S?(c) Calculate the value
Which of the following statements are true and which are false?(a) For the reaction 2A(g) + B(g) ⇋ A2B(g) Kc and Kp are numerically the same.(b) It is possible to distinguish Kc from Kp by
Consider the hypothetical reaction 2 A + B → 2 C + D. The following two-step mechanism is proposed for the reaction:Step 1: A + B → C + XStep 2: A + X → C + DX is an unstable intermediate.(a)
Which of the following statements are true and which are false?(a) The equilibrium constant can never be a negative number.(b) In reactions that we draw with a single-headed arrow, the equilibrium
The following diagrams represent equilibrium mixtures for the reaction A2 + B ⇌ A + AB at 300 K and 500K. The A atoms are red, and the B atoms are blue. Is the reaction exothermic or endothermic?
When lead (IV) oxide is heated above 300°C it decomposes according to the following reaction PbO2(s) ⇋ PbO(s) + O2(g). Consider the two sealed vessels of PbO2shown here. If both vessels are heated
Suppose that, in the absence of a catalyst, a certain biochemical reaction occurs x times per second at normal body temperature (37°C). In order to be physiologically useful, the reaction needs to
Snapshots of two hypothetical reactions, A(g) +B(g) ⇌ AB(g) and X(g) + Y(g) ⇌ XY(g) at five different times are shown here. Which reaction has a larger equilibrium constant? t = 10 s 20 s 30 s 40
As shown in Figure 14.24, the first step in the heterogeneous hydrogenation of ethylene is adsorption of the ethylene molecule on a metal surface. One proposed explanation for the “sticking” of
A solution is made by adding 0.300 g Ca(OH)2(s), 50.0 mL of 1.40 M HNO3, and enough water to make a final volume of 75.0 mL Assuming that all of the solid dissolves, what is the pH of the final
The following observations are made about a diprotic acid H2A:(i) A 0.10 M solution of H2A has pH = 3.30.(ii) A 0.10 M solution of the salt NaHA is acidic.Which of the following could be the value of
Succinic acid (H2C4H6O4), which we will denote H2Suc, is a biologically relevant diprotic acid with the structure shown below. It is closely related to tartaric acid and malic acid (Figure 16.1). At
Which of the following solutions is a buffer?(a) A solution made by mixing 100 mL of 0.100 M CH3COOH and 50 mL of 0.100 M NaOH(b) A solution made by mixing 100 mL of 0.100 M CH3COOH and 500 mL of
The graph below shows the solubility of a salt as a function of pH. Which of the following choices explain the shape of this graph?(a) None; this behavior is not possible.(b) A soluble salt reacts
A 0.25 M solution of a salt NaA has pH = 9.29. What is the value of Ka for the parent acid HA?
At 50°C, the ion-product constant for H2O has the value Kw = 5.48 × 10-14. What is the pH of pure water at 50°C?
Which of these statements about the common-ion effect is most correct?(a) The solubility of a salt MA is decreased in a solution that already contains either M+ or A-.(b) Common ions alter the
Consider the equilibriumB(aq) + H2O(I) ⇌ HB+(aq) + OH-(aq).Suppose that a salt of HB+ is added to a solution of B at equilibrium.(a) Will the equilibrium constant for the reaction increase,
Which of the following solutions is a buffer?(a) 0.10 M CH3COOH and 0.10 M CH3COONa(b) 0.10 M CH3COOH(c) 0.10 M HCl and 0.10 M NaCl(d) Both a and c(e) All of a, b, and c.
Compare the titration of a strong, monoprotic acid with a strong base to the titration of a weak, monoprotic acid with a strong base. Assume the strong and weak acid solutions initially have the same
For each statement, indicate whether it is true or false.(a) The solubility of a slightly soluble salt can be expressed in units of moles per liter.(b) The solubility product of a slightly soluble
The solubility of two slightly soluble salts of M2+ , MA and MZ2, are the same, 4 × 10-4 mol/L.(a) Which has the larger numerical value for the solubility product constant?(b) In a saturated
Rainwater is acidic because CO2(g) dissolves in the water, creating carbonic acid, H2CO3. If the rainwater is too acidic, it will react with limestone and seashells (which are principally made of
A weak monoprotic acid is titrated with 0.100 M NaOH. It requires 50.0 mL of the NaOH solution to reach the equivalence point. After 25.0 mL of base is added, the pH of the solution is 3.62. Estimate
Baking soda (sodium bicarbonate, NaHCO3) reacts with acids in foods to form carbonic acid (H2CO3), which in turn decomposes to water and carbon dioxide gas. In a cake batter, the CO2(g) forms bubbles
In non-aqueous solvents, it is possible to react HF to create H2F+. Which of these statements follows from this observation?(a) HF can act like a strong acid in non-aqueous solvents(b) HF can act
Rank the following gases from least dense to most dense at 1.00 atm and 298 K: SO2, HBr, CO2. Explain.
One of the molecular orbitals of the H2- ion is sketched below:(a) Is the molecular orbital a σ or π MO? Is it bonding or antibonding?(b) In H2-, how many electrons occupy the MO shown above?(c)
The vapor pressure of ethanol (C2H5OH) at 19°C is 40.0 torr. A 1.00-g sample of ethanol is placed in a 2.00 L container at 19°C. If the container is closed and the ethanol is allowed to reach
Naphalene, (C10H8) is the main ingredient in traditional mothballs. Its normal melting point is 81°C, its normal boiling point is 218°C, and its triple point is 80°C at 1000 Pa. Using the data,
The table below lists the density of O2 at various temperatures and at 1 atm. Graph the data and predict the substance’s normal boiling point.Temperature (K)
Consider the following XF4 ions: PF4-, BrF4-, ClF4+, and AlF4-.(a) Which of the ions have more than an octet of electrons around the central atom?(b) For which of the ions will the electrondomain and
Based on their composition and structure, list CH2Cl2, CH3CH2CH3, and CH3CH2OH in order of(a) Increasing intermolecular forces(b) Increasing viscosity(c) Increasing surface tension.
(a) What is the relationship between surface tension and temperature?(b) What is the relationship between viscosity and temperature?(c) Why do substances with high surface tension also tend to have
(a) Which is generally stronger, intermolecular interactions or intramolecular interactions?(b) Which of these kinds of interactions are broken when a liquid is converted to a gas?
At room temperature, Si is a solid, CCl4 is a liquid, and Ar is a gas. List these substances in order of(a) Increasing intermolecular energy of attraction(b) Increasing boiling point.
As a metal such as lead melts, what happens to(a) The average kinetic energy of the atoms(b) The average distance between the atoms?
Gas pipelines are used to deliver natural gas (methane, CH4) to the various regions of the United States. The total volume of natural gas that is delivered is on the order of 2.7 × 1012L per day,
An ideal gas at a pressure of 1.50 atm is contained in a bulb of unknown volume. A stopcock is used to connect this bulb with a previously evacuated bulb that has a volume of 0.800L as shown here.
A gas bubble with a volume of 1.0 mm3 originates at the bottom of a lake where the pressure is 3.0 atm. Calculate its volume when the bubble reaches the surface of the lake where the pressure is 730
WF6 is one of the heaviest known gases. How much slower is the root-mean-square speed of WF6 than He at 300 K?
Which assumptions are common to both kinetic-molecular theory and the ideal-gas equation?
Determine whether each of the following changes will increase, decrease, or not affect the rate with which gas molecules collide with the walls of their container:(a) Increasing the volume of the
If 5.15 g of Ag2O is sealed in a 75.0-mL tube filled with 760 torr of N2 gas at 32°C, and the tube is heated to 320°C, the Ag2O decomposes to form oxygen and silver. What is the total pressure
A rigid vessel containing a 3:1 mol ratio of carbon dioxide and water vapor is held at 200°C where it has a total pressure of 2.00 atm. If the vessel is cooled to 10°C so that all of the water
A 334-mL cylinder for use in chemistry lectures contains 5.225 g of helium at 23°C. How many grams of helium must be released to reduce the pressure to 75 atm assuming ideal gas behavior?
A 35.1 g sample of solid CO2 (dry ice) is added to a container at a temperature of 100 K with a volume of 4.0 L. If the container is evacuated (all of the gas removed), sealed and then allowed to
To derive the ideal-gas equation, we assume that the volumeof the gas atoms/molecules can be neglected. Given the atomic radius of neon, 0.69 Å, and knowing that a sphere has a volume of 4πr3/3,
(a) Amonton’s law expresses the relationship between pressure and temperature. Use Charles’s law and Boyle’s law to derive the proportionality relationship between P and T.(b) If a car tire is
You have a gas at 25 °C confined to a cylinder with a movable piston. Which of the following actions would double the gas pressure?(a) Lifting up on the piston to double the volume while keeping the
The graph below shows the change in pressure as the temperature increases for a 1-mol sample of a gas confined to a 1-L container. The four plots correspond to an ideal gas and three real gases: CO2,
Place the following molecules and ions in order from smallest to largest bond order: H2+, B2, N2+, F2+, and Ne2.
Suppose that silicon could form molecules that are precisely the analogs of ethane (C2H6), ethylene (C2H4), and acetylene (C2H2). How would you describe the bonding about Si in terms of hydrid
The structure of borazine, B3N3H6, is a six-membered ring of alternating B and N atoms. There is one H atom bonded to each B and to each N atom. The molecule is planar.(a) Write a Lewis structure for
Consider the molecule C4H5N, which has the connectivity shown below.(a) After the Lewis structure for the molecule is completed, how many s and how many p bonds are there in this molecule?(b) How
Which of the following statements about hybrid orbitals is or are true? (i) After an atom undergoes sp hybridization there is one unhybridized p orbital on the atom, (ii) Under sp2 hybridization,
In the formate ion, HCO2-, the carbon atom is the central atom with the other three atoms attached to it.(a) Draw a Lewis structure for the formate ion.(b) What hybridization is exhibited by the C
Consider the Lewis structure for glycine, the simplest amino acid:(a) What are the approximate bond angles about each of the two carbon atoms, and what are the hybridizations of the orbitals on each

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