Deck 4: Solution Chemistry and the Hydrosphere

Question 1

If there are 0.505 g of NaCl left in a beaker that originally contained 75.0 mL of saltwater, what must have been the concentration of the original solution?

A) 0.00647 M
B) 0.0115 M
C) 0.0673 M
D) 0.115 M
E) 0.673 M

Answer 1

0.115 M

Question 2

Diluting 1.0 mL of a 1.0 M solution to 1000 mL results in a solution that is 0.001 M. Repeating this 1000-fold dilution process five more times results in a concentration of __________

A) 1.0  10^-8 M.
B) 5.0  10^-3 M.
C) 1.0  10^-18 M.
D) 1.0  10^-9 M.
E) 2.0  10^-4 M.

Answer 2

1.0  10^-18 M.

Question 3

What volume of 12 M HCl solution needs to be diluted to produce 500 mL of 3.0 M HCl solution?

A) 125 mL
B) 250 mL
C) 500 mL
D) 2000 mL
E) 1000 mL

Answer 3

125 mL

Question 4

Which picture best represents an atomic-level view of a nonelectrolyte solution (water molecules not shown)?

A)
B)
C)
D)

Question 5

Determine the molar concentration of an aqueous solution of lead(II) nitrate solution that is 26 ppb (parts per billion) Pb(NO₃)₂.

A) 7.85  10^-14 M
B) 2.60  10^-8 M
C) 4.26  10^-11 M
D) 7.85  10^-8 M
E) 7.85  10^-11M

Question 6

Determine the molar concentration of ethanol (C₂H₆O) in a wine that is 14% ethanol by mass. The density of this wine is 0.93 g/cm³.

A) 0.063 M
B) 13.0 M
C) 0.14 M
D) 2.8 M
E) 3.0 M

Question 7

A chemistry student attempted to make a 0.2000 M solution of NaCl using a 100.0 mL volumetric flask. She added exactly 100.0 mL of water to the flask, then added 0.02000 mol of NaCl, and found that the total volume in the flask was above the 100.0 mL mark. What was the concentration of the solution?

A) exactly 0.2000 M
B) a bit less than 0.2000 M
C) a bit more than 0.2000 M
D) exactly 0.2002 M
E) There is insufficient information to select one of the above responses.

Question 8

In the dilution of 10.0 mL of a 0.10 M solution of HCl to a volume of 20.0 mL, what remains unchanged?

A) the moles of HCl in the solution
B) the concentration of the HCl solution
C) the volume of the HCl solution
D) the mass of the HCl solution
E) All of the above change.

Question 9

The proof of liquor is defined as the percentage of ethanol it contains times two. If vodka is 80 proof, what is the solvent in vodka?

A) vodka
B) water
C) ethanol
D) not enough information to answer
E) the same as the solute in this case

Question 10

How many grams of sodium chloride, NaCl, are needed to make up 1.00 L of a solution that is 2.00 M ?

A) 23.0 g
B) 29.2 g
C) 58.4 g
D) 117 g
E) 35.5 g

Question 11

Molarity, M, is defined as __________

A) moles of solute dissolved in 1 mol of solvent.
B) moles of solute dissolved in 1 kg of solvent.
C) moles of solute dissolved in 1 L of solvent.
D) moles of solute dissolved in 1 L of solution.
E) moles of solute dissolved in the solution.

Question 12

How many grams of solid magnesium chloride, MgCl₂, are needed to make 250 mL of 0.50 M solution?

A) 9.5 g
B) 48 g
C) 12 g
D) 125 g
E) 4.8 g

Question 13

Commercial hydrochloric acid is 12.1 M. What volume of commercial HCl solution should be used to prepare 250.0 mL of 3.00 M HCl?

A) 139 mL
B) 126 mL
C) 252 mL
D) 62.0 mL
E) 83.0 mL

Question 14

A salt solution is added to a marine aquarium. What mass of sodium chloride is needed to produce 250.0 mL of a solution that has a concentration of 0.0500 M ?

A) 731 g
B) 731 mg
C) 58.5 g
D) 2.92 mg
E) 2.92 g

Question 15

If 100 mL of 3.0 M solution were diluted to 250 mL, what would the concentration be?

A) 0.012 M
B) 0.12 M
C) 1.2 M
D) 12 M
E) 120 M

Question 16

If 120 g of NaOH were used to prepare 500 mL of solution, what would the concentration be?

A) 1 M
B) 2 M
C) 3 M
D) 4 M
E) 6 M

Question 17

Concentrated sulfuric acid contains 4 g of water for every 100 g of solution. The solvent is __________

A) water.
B) sulfuric acid.
C) concentrated.
D) the same as the solution.
E) the same as the solute in this case.

Question 18

A concentrated aqueous ammonia solution has a density of 0.90 g/mL and is 28.0% by mass ammonia. Determine the molar concentration of this solution.

A) 15 M
B) 1.5 M
C) 0.032 M
D) 31 M
E) 3.0 M

Question 19

What volume of 3.0 M NaOH contains 0.15 mole of NaOH?

A) 500 mL
B) 50 mL
C) 5.0 mL
D) 0.50 mL
E) 0.050 mL

Question 20

A homogeneous mixture of two or more substances is called __________

A) a compound.
B) an electrolyte.
C) a solution.
D) a solvent.
E) a mess.

Question 21

In a demonstration of strong electrolytes, weak electrolytes, and nonelectrolytes, Professor Popsnorkle used a lightbulb apparatus that showed how much a solution conducted electricity by the brightness of the lightbulb. When pure water was tested, the bulb did not light. Then Professor Popsnorkle tested the following aqueous solutions. Which one caused the bulb to burn dimly but not brightly?

A) table salt, NaCl
B) ethanol, CH₃CH₂OH
C) table sugar, C₁₂H₂₂O₁₁
D) acetic acid, CH₃COOH
E) methanol, CH₃OH

Question 22

Hydroxyapatite, [Ca₅(PO₄)₃(OH)], the major component of tooth enamel, is attacked and decomposed by acids more readily than fluorapatite, [Ca₅(PO₄)₃F]. Which one of the following reactions is analogous to the reaction of hydroxyapatite?

A) Ca(s) + 2HCl(aq) CaCl₂(s) + 2H⁺
B) CaF₂(s) + 2H⁺(aq) Ca²⁺(aq) + 2HF(aq)
C) Ca(OH)₂(s) + 2H⁺(aq) Ca²⁺(aq) + 2H₂O( )
D) Ca(s) + 2H⁺(aq) Ca²⁺(aq) + H₂(g)
E) Ca₃(PO₄)₂(s) + 6H⁺(aq)  3Ca²⁺(aq) + 2H₃PO₄(aq)

Question 23

Which picture best represents an atomic-level view of acetic acid, which is a weak acid, in aqueous solution (water molecules not shown)?

A)
B)
C)
D)

Question 24

What is the molar concentration of sodium in a 200.0 mL solution prepared from 1.223 g of sodium phosphate (Na₃PO₄, 163.9 g/mol), which is a cleaning agent, food additive, and stain remover?

A) 0.03731 M
B) 0.2486 M
C) 0.7338 M
D) 0.1119 M
E) 0.1243 M

Question 25

Identify the acid in the following acid-base reaction. PbCO₃(s) + H₂SO₄(aq)  PbSO₄(s) + CO₂(g) + H₂O( )

A) PbCO₃(s)
B) CO₂(g)
C) PbSO₄(s)
D) H₂O( )
E) H₂SO₄(aq)

Question 26

Identify the base in the following acid-base reaction. PbCO₃(s) + H₂SO₄(aq)  PbSO₄(s) + CO₂(g) + H₂O( )

A) CO₃^2-
B) CO₂
C) SO₄^2-
D) H₂O
E) H₂SO₄

Question 27

Chalk contains calcium carbonate. What would be the best solution for cleaning a sidewalk that a preschool class covered with smiling suns, flowers, birds, rainbows, and houses using sidewalk chalk?

A) ammonia
B) plain water
C) vinegar
D) paint thinner
E) olive oil

Question 28

Which one of the following statements regarding a weak acid is not correct?

A) A weak acid ionizes only to a small extent in water.
B) A weak acid ionizes in water to produce hydronium ions.
C) A weak acid neutralizes bases.
D) Acetic acid is an example.
E) A weak acid has a very low concentration.

Question 29

In a demonstration of strong electrolytes, weak electrolytes, and nonelectrolytes, Professor Popsnorkle used a lightbulb apparatus that showed how much a solution conducted electricity by the brightness of the lightbulb. When pure water was tested, the bulb did not light. When some acetic acid was added to the water, the bulb burned dimly. When more acetic acid was added to the solution, the bulb burned a little more brightly. In his frustration to make the bulb shine brightly with acetic acid, Professor Popsnorkle started over by testing the beaker of the pure acetic acid. What was the result?

A) The bulb did not light.
B) The bulb burned dimly.
C) The bulb burned more than any of the others but still not brightly.
D) The bulb burned brightly.
E) Professor Popsnorkle was electrocuted.

Question 30

In a demonstration of strong electrolytes, weak electrolytes, and nonelectrolytes, Professor Popsnorkle used a lightbulb apparatus that showed how much a solution conducted electricity by the brightness of the lightbulb. When pure water was tested, the bulb did not light. Then Professor Popsnorkle tested the following aqueous solutions. Which one caused the bulb to burn the brightest?

A) table salt, NaCl
B) ethanol, CH₃CH₂OH
C) table sugar, C₁₂H₂₂O₁₁
D) acetic acid, CH₃COOH
E) methanol, CH₃OH

Question 31

Which contains more solute particles: a 0.10 M aqueous solution of methanol (CH₃OH) or a 0.10 M aqueous solution of salt (NaCl)?

A) They contain the same number of solute particles.
B) The salt solution contains twice as many particles as the methanol solution.
C) The methanol solution contains three times as many particles as the salt solution.
D) Neither solution contains solute particles.
E) The methanol solution contains twice as many particles as the salt solution.

Question 32

Ammonia (NH₃) is a weak base that reacts with a strong acid to form the ammonium ion, NH₄⁺. If 5.00 mL of a solution of an ammonia cleaner is titrated directly with 42.6 mL of 0.5000 M HCl, what is the concentration of the NH₃ in solution? (Assume that the ammonia is the only solute that reacts with the acid.)

A) 0.0587 M
B) 0.107 M
C) 4.26 M
D) 1.07 M
E) 5.87 M

Question 33

If the molar concentration of sodium sulfate (Na₂SO₄) is 0.10 M, what is the concentration of sodium ion?

A) 0.10 M
B) 0.050 M
C) 0.20 M
D) 0.30 M
E) 0.40 M

Question 34

What would be the products in the ionic equation for the following reaction? 2HBr(aq) + 2KOH(aq)  products
I. K⁺(aq) and Br^-(aq);
II. KH(aq);
III. H₂O( );
IV. KBr(s); V. BrOH(aq); VI. KBr(aq)

A) I and III
B) III and IV
C) III and VI
D) II, III, and V
E) II and V

Question 35

In its reaction with water, ammonia (NH₃) __________

A) acts as an acid.
B) acts as a base.
C) acts neither as an acid nor as a base.
D) serves as both an acid and as a base.
E) causes a precipitate to form.

Question 36

Which one of the following statements regarding a strong acid is not correct?

A) A strong acid ionizes completely in water.
B) A strong acid ionizes in water to produce hydronium ions.
C) A strong acid neutralizes bases.
D) HCl is an example.
E) A strong acid is highly concentrated.

Question 37

Calcium hydroxide is slightly soluble in water. About 1 gram will dissolve in 1 liter. What are the spectator ions in the reaction of such a dilute solution of calcium hydroxide with hydrochloric acid?

A) Ca²⁺ and Cl^-
B) Ca²⁺ and OH^-
C) H₃O⁺ and OH^-
D) H₃O⁺ and Cl^-
E) Ca²⁺, Cl^- , H₃O⁺, and OH^-

Question 38

Two phosphoric acid molecules can combine to make pyrophosphoric acid and another molecule as shown here. The pyrophosphoric acid molecule is a phosphoester and is a structural element in the ADP/ATP metabolic energy system. What molecule is represented by the question mark in the structural reaction equation below?

A) O₂
B) OH^-
C) H₂O
D) PO
E) H₂

Question 39

If 50.0 mL of a 0.10 M solution of sodium chloride is mixed with 50.0 mL of 0.10 M magnesium chloride, what is the molar concentration of chloride in the resulting solution?

A) 0.10 M
B) 0.20 M
C) 0.05 M
D) 0.15 M
E) 0.25 M

Question 40

A cross section of a Mad-Dawg gumball shows an outer layer of citric acid and malonic acid, beneath that a layer of food coloring, sugar, and flavoring, beneath that a layer of sodium bicarbonate (NaHCO₃), and finally in the middle-gum! A 12-year-old puts one in his mouth and immediately puckers, smiles, and then foams at the mouth before chewing. Where did the foam come from?

A) Twelve-year-olds naturally foam at the mouth.
B) The sodium bicarbonate explodes when exposed to moisture.
C) The acids react with the sodium bicarbonate, making unstable carbonic acid.
D) The foam must have been packed in the gum somewhere.
E) The acids react with the sugar making carbon volcano.

Question 41

Sodium metal easily loses an electron to form the sodium ion. In this process, sodium is __________

A) reduced.
B) oxidized.
C) ionized.
D) complexed.
E) both ionized and oxidized.

Question 42

In a titration, the solution of known concentration delivered by the buret is called the titrant, and the solution being titrated is called the analyte. To carry out a calculation to determine an unknown concentration of a sample from titration data, one would need all of the following data except __________

A) the volume of the titrant delivered.
B) the volume of the analyte.
C) the stoichiometry of the reaction between the titrant and the analyte.
D) the concentration of the analyte.
E) the concentration of the titrant.

Question 43

If 1.0 L of 1.0 M HCl spilled and needed to be neutralized, how many grams of the solid sodium carbonate (Na₂CO₃, 106 g/mol) would be required?

A) 53 g
B) 106 g
C) 1060 g
D) 530 g
E) 212 g

Question 44

What mass of silver chloride will be recovered if excess sodium chloride is added to 500 mL of solution containing 10.79 g of Ag⁺?

A) 10.8 g
B) 21.6 g
C) 28.6 g
D) 7.2 g
E) 14.3 g

Question 45

Ion-exchange resins can remove Mg²⁺ and Ca²⁺ in water (called softening) by releasing Na⁺. What would be the concentration of sodium ion in the softened water if the combined concentration of these Group 2A ions that were removed from the hard water was 0.026 M?

A) 0.052 M
B) 0.26 M
C) 0.13 M
D) 0.00 M
E) Can't tell, necessary information is lacking.

Question 46

Sodium thiosulfate (Na₂S₂O₃, molar mass = 158.2 g/mol) is used in photography. Your summer job is at a photography lab and you need to check the purity of an outdated supply. You react 40.21 mL of 0.246 M iodine solution with a 3.232 g sample. What is the percent purity of the sodium thiosulfate that you report to your boss? I₂(aq) + 2S₂O₃^2-(aq)  2I^-(aq) + S₄O₆^2-(aq)

A) 100%
B) 48.4%
C) 96.8%
D) 98.6%
E) 84.4%

Question 47

If one regular antacid tablet contains 500 mg of solid CaCO₃ (100 g/mol), how many mL of 1.0 M stomach acid (HCl) could it neutralize?

A) 5 mL
B) 10 mL
C) 50 mL
D) 100 mL
E) 15 mL

Question 48

A reaction that takes place between dissolved barium nitrate and dissolved sodium sulfate results in formation of solid barium sulfate. Which equation describes this reaction?

A) Ba(NO₃)₂(aq) + Na₂SO₄(aq)  BaSO₄(s) + 2NaNO₃(aq)
B) BaNO₃(aq) + NaSO₄(aq)  BaSO₄(s) + NaNO₃(aq)
C) 2Ba(NO₃)(aq) + Na₂SO₄(aq)  Ba₂SO₄(s) + 2NaNO₃(aq)
D) Ba(NO₃)₂(aq) + 2NaSO₄(aq)  Ba(SO₄)₂(s) + 2NaNO₃(aq)
E) Ba(NO₃)₂(aq) + Na₂SO₄(aq)  BaSO₄(aq) + 2NaNO₃(s)

Question 49

In carrying out a titration of a hydrochloric acid solution with a standard sodium hydroxide solution, a student went beyond the end point before reading the volume on the buret. That is, the volume used was larger than the volume required to reach the end point. How will this error affect the calculated concentration of the hydrochloric acid?

A) The calculated concentration will be larger than the actual concentration.
B) The calculated concentration will be smaller than the actual concentration.
C) The calculated concentration will be the correct concentration.
D) There is no way to tell how this error will affect the calculation.
E) The calculated concentration will be the actual concentration.

Question 50

Most chloride salts are soluble. Identify an exception to this generalization.

A) AgCl
B) CaCl₂
C) MgCl₂
D) BaCl₂
E) NaCl

Question 51

Water-soluble toxic chromium compounds are waste products of electroplating operations, but the chromium can be precipitated as Cr(OH)₃ to remediate the water. How much 1.0 M NaOH solution is needed to remove the chromium from 100 L of a solution that is 0.001 M in Cr³⁺?

A) 100 mL
B) 300 mL
C) 10 L
D) 30 L
E) 33 L

Question 52

Tube worms that survive near geothermal vents of hydrogen sulfide rely on bacteria living inside them to obtain energy by the oxidation of H₂S to SO₄^2-. What is the overall change in the oxidation number of sulfur for this reaction?

A) -2
B) +2
C) -6
D) +8
E) +10

Question 53

A 500 mg dietary supplement of L-lysine (an amino acid, 146.2 g/mol) required 68.4 mL of 0.100 M NaOH to reach the end point. How many protons were removed for each L-lysine molecule in this titration?

A) 1
B) 2
C) 3
D) 0.500
E) 2.5

Question 54

Magnesium hydroxide is insoluble. Write the net ionic equation for the reaction that takes place between a solution of magnesium chloride and a solution of sodium hydroxide.

A) MgCl₂(aq) + NaOH(aq) MgOH(s) + NaCl₂(aq)
B) MgCl₂(aq) + 2NaOH(aq) Mg(OH)₂(s) + 2NaCl(aq)
C) Mg²⁺(aq) + 2OH^-(aq) Mg(OH)₂(s)
D) Mg²⁺(aq) + 2Cl^- (aq) + 2Na⁺(aq) + 2OH^-(aq) Mg(OH)₂(s) + 2NaCl(s)
E) Mg²⁺(aq) + OH^-(aq) MgOH(s)

Question 55

Hard water contains Mg²⁺ and Ca²⁺ ions and tends to form a ring in a bathtub due to its reaction with the soluble anions in soap. The formation of this insoluble material is an example of __________

A) an acid-base reaction.
B) a precipitation reaction.
C) a redox reaction.
D) a bathochromic shift.
E) bad housekeeping.

Question 56

How many liters of 0.200 M NaOH solution are required to completely react with 1.00 L of 0.100 M HCN solution to produce sodium cyanide and water?

A) 0.25 L
B) 0.50 L
C) 1.00 L
D) 1.50 L
E) 2.00 L

Question 57

Silver salts are used in black-and-white photography. Owing to the value of silver, the ions left in developing solutions are often collected by precipitation reactions for recycling. A 4.5 L jug of a developing solution was treated with an excess of sodium chloride, and a precipitate containing 2.86 g of dry silver chloride was collected. What was the molar concentration of the silver ions in the developing solution? The net ionic equation is Ag⁺(aq) + Cl^-(aq) AgCl(s)

A) 2.9 M
B) 5.9  10^-3 M
C) 2.9  10^-3 M
D) 4.4  10^-3 M
E) 4.4 M

Question 58

Which of the following ionic compounds is insoluble in water?

A) BaCl₂
B) BaSO₄
C) NaOH
D) Ba(NO₃)₂
E) MgCl₂

Question 59

Which of the following compounds is most soluble in water?

A) AgCl
B) CaCO₃
C) Al(OH)₃
D) K₂SO₄
E) MgS

Question 60

Polymers with ionic functional groups have been developed for removal of ions from water. One example is Amberlite. One form of Amberlite has the structure shown below, where the -SO₃H groups act like a weak acid. What type of ions will this polymer attract?

A) cations
B) anions
C) all ions
D) impossible to tell
E) none, since the polymer is neutral

Question 61

Potassium is a very reactive metal. Many of its compounds are not very reactive. For example, some class B fire extinguishers contain potassium bicarbonate as a dry powder for use in extinguishing burning liquids. Why is there such a difference in the reactivity of potassium in the bicarbonate salt and potassium that is a combustible metal?

A) The difference in reactivity really is not that great to warrant an explanation.
B) The potassium atom is bonded to an oxygen atom in the bicarbonate salt but is unbonded in the metal and free to react.
C) The potassium metal possesses one additional electron that is easily transferred to other substances; the potassium in the bicarbonate salt already has lost this reactive electron.
D) The potassium in the bicarbonate salt is a base, but the potassium metal is an acid.
E) The potassium in the bicarbonate salt is an acid, but the potassium metal is a base.

Question 62

What is the oxidation number of P in H₂PO₄^-?

A) -5
B) -6
C) 5
D) 6
E) 4

Question 63

In which one of the following compounds is the oxidation number of S equal to +4?

A) H₂S
B) S₂Cl₂
C) MgSO₄
D) S₈
E) Na₂SO₃

Question 64

What is meant by the terms solution, solvent, and solute?

Question 65

The thermite reaction is used in welding applications and chemistry demonstrations because it releases a tremendous amount of energy. Which of the following statements is not correct regarding this reaction? 8Al + 3Fe₃O₄ 9Fe + 4Al₂O₃

A) Aluminum is oxidized.
B) Iron is reduced.
C) The oxidation number of Al changes from 0 to +3.
D) Aluminum is the reducing agent.
E) Three electrons are transferred from each aluminum atom to each iron atom.

Question 66

In a spontaneous oxidation-reduction reaction between aluminum and silver ion, the aluminum(III) ion and solid silver are formed. If 0.1 mol of aluminum is consumed in this reaction, how much silver will be produced?

A) 0.3 mol
B) 0.1 mol
C) 1.0 mol
D) 3 mol
E) 0.2 mol

Question 67

Magnesium metal burns brightly in the air to make a white powder. What are the likely products?

A) Mg(H₂O) and MgO₂
B) MgCO₃ and MgCO
C) Mg₂N₃ and Mg₂O
D) Mg₃N₂ and MgO
E) MgNO

Question 68

Chalk is mostly calcium carbonate. Could chalk-dust catch fire and burn in air?

A) Yes, the carbon in the chalk would burn.
B) Yes, calcium is a reactive metal that will burn.
C) No, calcium carbonate is completely oxidized.
D) No, the manufacturer puts a protective coating on chalk so that it will not burn.
E) No, the ignition temperature is extremely high.

Question 69

In which compound does chlorine have an oxidation number of +5?

A) HClO₄
B) HClO₃
C) HClO₂
D) HClO
E) HCl

Question 70

The carbon cycle characterizes the cyclic transformations of the element carbon through the environment and biomass. Some of the important species in this cycle are CO₂, CO₃^2-, C₆H₁₂O₆, and CH₄. Which of these compounds would undergo complete oxidation by O₂ to give the largest change in oxidation number?

A) CO₂
B) CO₃^2-
C) C₆H₁₂O₆
D) CH₄
E) CO₂ and CO₃^2- are equivalent in this regard.

Question 71

When the oxidation-reduction reaction shown here is balanced, how many electrons are transferred for each atom of copper that reacts? Ag⁺(aq) + Cu(s) Ag(s) + Cu²⁺(aq)

A) 1
B) 2
C) 3
D) 4
E) 0

Question 72

The drinking water standard of the World Health Organization (WHO) for arsenic is 10.0 g/L. What is this standard in parts per billion (ppb)?

Question 73

Chlorine, ozone, and chlorine dioxide are all common disinfectants for municipal water purification. What chemical property do they all share?

A) They are all strong acids.
B) They are all good oxidizing agents.
C) They are all good reducing agents.
D) They all form precipitates with a wide range of contaminants.
E) They are all strong bases.

Question 74

One type of alcohol breathalyzers used by law enforcement involves the following reaction. The amount of ethanol present is determined by a change in color of the solution. What type of reaction is this? 3CH₃CH₂OH(g) + 2K₂Cr₂O₇(aq) + 8H₂SO₄(aq) 
3CH₃COOH(aq) + 2Cr₂(SO₄)₃(aq) + 2K₂SO₄(aq) + 11H₂O

A) base ionization
B) acid ionization
C) acid-base neutralization
D) oxidation-reduction
E) dissociation

Question 75

The half-reaction for the reduction of molecular oxygen to water is __________

A) O₂(g)  H₂O( ).
B) O₂(g) + H₂(g) H₂O( ).
C) O₂(g) + H₂(g) + 2e^- H₂O( ).
D) O₂(g) + 2 H⁺(g) + 2e^- H₂O( ).
E) O₂(g) + 2 H⁺(g) H₂O( ) + 2e^-.

Question 76

Lead sinkers used for saltwater fishing do not react with sodium ions in the water. From this we can infer that __________

A) lead can reduce sodium ions.
B) sodium ions can reduce lead.
C) lead is heavier than sodium.
D) sodium ions cannot oxidize lead.
E) sodium ions cannot reduce lead.

Question 77

The oxidation number of carbon in carbon dioxide is

A) +2
B) -2
C) +4
D) -4
E) +1

Question 78

Nitrogen-fixing bacteria and plants are capable of converting atmospheric nitrogen to ammonia. This process is an example of __________

A) an acid-base reaction.
B) a precipitation reaction.
C) an oxidation reaction.
D) a reduction reaction.
E) ion exchange.

Question 79

Methane (CH₄) is a suitable fuel for burning because it is readily oxidized by oxygen gas, forming carbon dioxide and water. Hydrogen is also a good fuel for burning with oxygen gas, forming water as a product. What change in oxidation number always accompanies oxidation?

A) a decrease
B) an increase
C) no change
D) The change varies with the reaction.
E) Oxidation number increases by 1 unit.

Question 80

In the following reactions, which element is oxidized? Cu + FeSO₄  Fe + CuSO₄

A) Cu
B) Fe
C) S
D) O
E) None, this is not a redox reaction.