Deck 16: Additional Aqueous Equilibria: Chemistry and the Oceans

Question 1

What reaction occurs as a hydrochloric acid solution is added to a solution containing equal concentrations of acetic acid and sodium acetate?

A)
B)
C)
D)
E)

Answer 1

Question 2

When sodium chloride is added to a saturated solution of lead(II) chloride, some of the lead(II) chloride precipitates. This phenomenon is called ________

A)the common-ion effect.
B)selective precipitation.
C)supersaturation.
D)a solubility anomaly.
E)deionization.

Answer 2

the common-ion effect.

Question 3

A solution that contains a weak acid and its conjugate base in roughly equal concentrations is ________

A)neither acidic or basic.
B)a half-acid solution.
C)a buffer.
D)a heterogeneous mixture.
E)neutral.

Answer 3

a buffer.

Question 4

Which of the following is not a buffer system? A solution containing roughly equal concentrations of ________

A)fluoride ion and hydrofluoric acid.
B)bromide ion and hydrobromic acid.
C)phosphate ion and hydrogen phosphate ion.
D)carbonate ion and hydrogen carbonate ion.
E)phosphoric acid and dihydrogen phosphate ion.

Question 5

What is the pH of a buffer solution where [HA]  [A^]?

A)pH  1
B)pH  K_a
C)pH  pK_a
D)pH  pOH
E)pH  7.0

Question 6

Which of the following cannot be mixed together in water to produce a buffer solution?

A)NH₃ and HCl
B)HF and KF
C)HClO₃ and NaClO₃
D)HCN and NaOH
E)HNO₃ and NaNO₃

Question 7

Which of the following would be the best choice for preparing a buffer with a pH  3.5?

A)a solution of formic acid and sodium formate, K_a  1.8  10^4
B)a solution of acetic acid and sodium acetate, K_a  1.8  10^5
C)a solution of hypochlorous acid and sodium hypochlorite, K_a  3.5  10^8
D)a solution of boric acid and sodium borate, K_a  5.8  10^10
E)All of these solutions would be equally good choices for making this buffer.

Question 8

What is the pH of a solution containing 0.30 M lactic acid and 0.50 M of lactate ion (K_a for lactic acid  1.38  10^4)?

A)9.92
B)10.36
C)3.86
D)4.08
E)3.64

Question 9

Which one of the following would make the best buffer? (Ac  acetate)

A)a solution of hydrochloric acid and sodium chloride, HCl and NaCl
B)a solution of acetic acid and ammonia, NaAc and NH₃
C)a solution of acetic acid and ammonium chloride, HAc and NH₄Cl
D)a solution of sodium acetate and ammonium chloride, NaAc and NH₄Cl
E)a solution of ammonia and ammonium chloride, NH₃ and NH₄Cl

Question 10

Which of the following can be mixed together in water to produce a buffer solution?

A)HClO₄ and NaClO₄
B)HNO₃ and NaNO₃
C)H₂SO₄ and NaHSO₄
D)H₃PO₄ and NaH₂PO₄
E)HCl and NaCl

Question 11

Phenylephrine (PE, see the structure below) is a nasal decongestant and is the active ingredient in Sudafed, which contains phenylephrine hydrochloride (PEHCl). This conjugate acid of phenylephrine (PEH^) has a pK_a  5.5. At a physiological pH of 7.4, what is the ratio of concentrations, [PE]/[PEH^]?

A)6.7
B)0.01
C)0.14
D)79
E)21

Question 12

Which combination of solutions is the best choice for making a buffer solution?

A)equal volumes of 1 M ammonia (NH₃) and 0.001 M ammonium chloride (NH₄Cl)
B)equal volumes of 0.5 M hydrochloric acid (HCl) and 0.5 M sodium hydroxide (NaOH)
C)equal volumes of 0.5 M hydrochloric acid (HCl) and 0.5 M sodium chloride (NaCl)
D)equal volumes of 2 M ammonia (NH₃) and 1 M hydrochloric acid (HCl)
E)equal volumes of 2 M ammonium chloride (NH₄Cl) and 1 M hydrochloric acid (HCl)

Question 13

Research with biochemical systems commonly requires buffers because ________

A)that's just the way it is.
B)proteins have a critical pH dependence in their structure and function.
C)proteins decompose into constituent amino acids outside a certain pH range.
D)proteins are buffers.
E)salts are involved.

Question 14

The pK_a of a weak acid was determined to be 3.39 by measuring the pH of a solution containing the weak acid at 0.20 M and its conjugate base. The measured pH was 3.27. What was the concentration of the conjugate base?

A)0.26 M
B)0.15 M
C)0.20 M
D)0.050 M
E)0.35 M

Question 15

Suppression of the solubility of one ion by the addition of the counter-ion in its insoluble salt is known as the ________

A)ionic suppression effect.
B)counter-ion effect.
C)common-ion effect.
D)excession effect.
E)supersaturation effect.

Question 16

How many moles of sodium acetate must be added to 500 mL of 0.25 M acetic acid solution to produce a buffer with a pH of 4.94? The pK_a of acetic acid is 4.74. You can neglect the change in volume when sodium acetate dissolves in the acetic acid solution.

A)0.011 moles
B)0.021 moles
C)0.125 moles
D)0.198 moles
E)0.206 moles

Question 17

Which of the following would be the best choice for preparing a buffer with a pH  8.0?

A)a solution of formic acid and sodium formate, K_a  1.8  10^4
B)a solution of acetic acid and sodium acetate, K_a  1.8  10^5
C)a solution of hypochlorous acid and sodium hypochlorite, K_a  3.5  10^8
D)a solution of boric acid and sodium borate, K_a  5.8  10^10
E)All of these solutions would be equally good choices for making this buffer.

Question 18

A buffer system is set up with [HA]  2[A^]. If pK_a  5.5, what is the pH of the buffer?

A)5.2
B)5.8
C)7.5
D)3.5
E)7.0

Question 19

The pK_a of a weak acid was determined by measuring the pH of a solution containing the weak acid at 0.40 M and its conjugate base at 0.60 M. The measured pH was 7.8. What is the pK_a of the weak acid?

A)8.0
B)7.8
C)7.6
D)7.0
E)7.4

Question 20

Identify all the correct statements about an acid-base buffer solution.
I. It can be prepared by combining a strong acid with a salt of its conjugate base.
II. It can be prepared by combining a weak acid with a salt of its conjugate base.
III. It can be prepared by combining a weak base with its conjugate acid.
IV. The pH of a buffer solution does not change when the solution is diluted.
V. A buffer solution resists changes in its pH when an acid or base is added to it.

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

Question 21

Acid-base indicators change color ________

A)exactly when pH  pK_a of the indicator.
B)generally over a range of 1 or 2 pH units.
C)at pH  7.
D)always between a pH of 6 and 8.
E)at the midpoint of a titration.

Question 22

Acid-base indicators need to have very intense colors so that a very low concentration is visible. Could there be a problem in using too much indicator?

A)No, the colors would just be darker.
B)No, indicators are inert.
C)Yes, more indicator requires more extreme pH values to change color.
D)Yes, the indicator could affect the acid-base chemistry being measured.
E)No, the colors would just be sharper.

Question 23

A solution of benzoic acid (0.21 M, 25.00 mL), a monoprotic acid, was titrated with 53.10 mL of 0.10 M sodium hydroxide (K_a of benzoic acid  6.46  10^5). What is the final pH of this solution?

A)3.11
B)1.17
C)7.00
D)12.83
E)10.89

Question 24

The most suitable acid-base indicator for a titration of acetic acid with NaOH has ________

A)a pK_in  pK_a of the acid.
B)a pK_in  pK_b of the base.
C)pK_in  pH of a sodium acetate solution.
D)pK_in  pH of an acetic acid solution.
E)pK_in  7.0.

Question 25

To simulate the pH of blood, which is 7.4, an undergraduate researcher in a biology lab produced a buffer solution by dissolving sodium dihydrogen phosphate (K_a  6.2  10^8) and disodium hydrogen phosphate (K_a  3.6  10^13) together in an aqueous solution. What mole ratio of Na₂HPO₄/NaH₂PO₄ did she need to use?

A)1.2
B)1.6
C)0.90
D)1.0
E)0.96

Question 26

At what point in the following titration curve for a weak acid being titrated with a strong base is the pH equal to the pK_a of the acid? The x-axis scale goes from 0.0 mL to 20.0 mL. The sharp rise is at 10.0 mL.

A)0.0 mL
B)5.0 mL
C)9.0 mL
D)10.0 mL
E)18.0 mL

Question 27

A solution of formic acid (0.15 M, 15.00 mL), a monoprotic acid, was titrated with 18.50 mL of 0.10 M sodium hydroxide (K_a of formic acid  1.80  10^4). What is the final pH of this solution?

A)3.08
B)4.41
C)7.00
D)9.59
E)10.92

Question 28

Bromocresol green is yellow in its acidic form and blue in its basic form. When is it green?

A)at the equivalence point in a titration
B)in its neutral form
C)when the solution pH equals its pK_a
D)when the solution pH equals 7
E)at the midpoint in a titration

Question 29

Glycolic acid, which is a monoprotic acid and a constituent in sugar cane, has a pK_a of 3.9. A 25.0 mL solution of glycolic acid is titrated to the stoichiometric point with 35.8 mL of 0.020 M sodium hydroxide solution. What is the pH of the resulting solution at the stoichiometric point?

A)4.12
B)9.88
C)6.01
D)7.98
E)Sufficient information is not provided to determine the pH.

Question 30

Lactic acid, which is found in milk products, has a pK_a of 3.85. A 50.0 mL solution of 0.05 M lactic acid is titrated with 0.025 M sodium hydroxide. What is the pH of the solution after 64.0 mL of the sodium hydroxide has been added?

A)3.85
B)3.60
C)9.90
D)4.10
E)7.00

Question 31

The following titration curve is most likely to be associated with ________

A)the titration of a strong acid with a strong base titrant.
B)the titration of a weak acid with a strong base titrant.
C)the titration of a strong base with a strong acid titrant.
D)the titration of a weak base with a strong acid titrant.

Question 32

Halfway to the equivalence point in a titration curve of a weak acid with a strong base, ________

A)nothing is happening yet.
B)the pH  pK_a of the weak acid.
C)pH  3.5 exactly.
D)pH  pK_a of the indicator.
E)the pH has not yet changed.

Question 33

A 25.0 mL solution of quinine was titrated with 1.00 M hydrochloric acid, HCl. It was found that the solution contained 0.125 moles of quinine. What was the pH of the solution after 50.00 mL of the HCl solution were added? Quinine is monobasic with pK_b  5.10.

A)5.10
B)8.90
C)8.72
D)4.92
E)9.08

Question 34

The following titration curve is most likely to be associated with

A)the titration of a strong acid with a strong base titrant.
B)the titration of a weak acid with a strong base titrant.
C)the titration of a strong base with a strong acid titrant.
D)the titration of a weak base with a strong acid titrant.

Question 35

A 0.500 g sample of an unknown substance was titrated with a 0.1 M HCl solution. Another 0.500 g sample of it was titrated with a 0.1 M NaOH solution. The resulting titration curves are illustrated here. Given the following possibilities, what is the sample?

A)Na₂CO₃
B)NaHCO₃
C)H₂CO₃
D)CO₂
E)There is no way to tell.

Question 36

What is indicated by the shape of the titration curve?

A)A diprotic acid was titrated with a strong base.
B)A triprotic acid was titrated with a strong base.
C)A diprotic base was titrated with a strong acid.
D)A triprotic base was titrated with a strong acid.
E)A strong acid was titrated with a strong base.

Question 37

In a titration of monoprotic acids and bases, there is a large change in pH ________

A)at the point where pH  pK_a of the acid.
B)when the volume of acid is exactly equal to the volume of base.
C)when the concentration of acid is exactly equal to the concentration of base.
D)when the number of moles of acid is exactly equal to the number of moles of base.
E)at the point where pH  pK_b of the base.

Question 38

When an acetic acid solution is titrated with sodium hydroxide, the slope of the titration curve (pH versus volume of NaOH added) increases when sodium hydroxide is first added. This change shows that ________

A)nothing is happening during this part of the titration.
B)the reaction is very slow during this part of the titration.
C)a more concentrated solution of NaOH needs to be present to initiate the reaction.
D)acetic acid is being converted to sodium acetate.
E)the pH is not affected until all the acetic acid is consumed.

Question 39

What are the characteristics of a pH indicator? A pH indicator ________
I. is a weak acid.
II. has different characteristic colors in protonated and unprotonated forms.
III. changes color when the pH is near its pK_a.

A)I only
B)II only
C)both II and III
D)I, II, and III
E)I and III

Question 40

You have a summer job as an intern in an analytical chemistry laboratory. You are about to titrate a solution of nicotine (pK_b  6.0), which is a base similar to ammonia, with a standard hydrochloric acid solution. Two pH indicators are available for you to use: thymol blue (pK_a  3.47) and phenolphthalein (pK_b  9.4). Which indicator do you select as being the more appropriate one to use?

A)Both indicators would work equally well because at the equivalence point the pH of the solution changes very sharply from strongly basic to strongly acidic.

B)Phenolphthalein is the better choice because it is one of the most commonly used pH indicators.
C)Neither of these indicators would work because their pK_a values are not close to 7.00, which is the pH of the solution at the equivalence point.
D)Phenolphthalein is the better choice because the sample pH at the equivalence point will be close to the pK_a value of 9.4.
E)Thymol blue is the better choice because the sample pH at the equivalence point will be close to the pK_a value of 3.47.

Question 41

A solution of ammonia (0.12 M, 15.00 mL) was titrated with 0.2 M hydrochloric acid (K_b of ammonia  1.8  10^5). What is the pH at the equivalence point?

A)3.75
B)5.19
C)7.00
D)8.81
E)10.25

Question 42

Identify the Lewis base in the following reaction:

A)PH₃
B)H^
C)PH₄^
D)None of these is a base.
E)All of these are bases.

Question 43

Identify the Lewis acid in the following reaction:

A)BF₃
B)F^
C)BF₄^
D)None of these is an acid.
E)All of these are acids.

Question 44

A solution of sulfuric acid (H₂SO₄, 25.00 mL) was titrated to completion with 34.55 mL of 0.1020 M sodium hydroxide. What was the concentration of the sulfuric acid?

A)0.07048 M
B)0.1410 M
C)0.2819 M
D)0.0353 M
E)0.0533 M

Question 45

A phosphate buffer solution (25.00 mL sample) used for a growth medium was titrated with 0.1000 M hydrochloric acid. The components of the buffer were sodium monohydrogen phosphate and sodium dihydrogen phosphate. The first endpoint occurred at a volume of 10.32 mL, and the second occurred after an additional 18.62 mL was added, for a total volume of 28.94 mL. What was the total concentration of phosphate (in any form) in the buffer?

A)0.03992 M
B)0.1198 M
C)0.04243 M
D)0.07448 M
E)0.08382 M

Question 46

One brand of extra-strength antacid tablets contains 750 mg of calcium carbonate (100 g/mol) in each tablet. Stomach acid is essentially a hydrochloric acid solution. Is so much calcium carbonate really needed to neutralize stomach acid? Calculate the volume of stomach acid with a pH of 1.0 that one of these tablets could neutralize, and compare that value with the normal volume of stomach fluid, which usually is about 100 mL. One tablet can neutralize ________ mL of stomach acid at a pH of 1.0.

A)75
B)150
C)250
D)15
E)7.5

Question 47

A solution of hydrofluoric acid (0.27 M, 10.00 mL) was titrated with 15.0 mL of 0.13 M sodium hydroxide (K_a of hydrofluoric acid  7.20  10^4). What is the final pH of this solution?

A)3.33
B)3.56
C)4.57
D)10.44
E)11.27

Question 48

A Lewis acid is ________

A)a proton donor.
B)a proton acceptor.
C)an electron-pair donor.
D)an electron-pair acceptor.
E)never viewed also as a Brønsted-Lowry acid.

Question 49

A solution of hydrochloric acid (HCl, 25.00 mL) was titrated to completion with 34.55 mL of 0.1020 M sodium hydroxide. What was the concentration of the hydrochloric acid?

A)0.07048 M
B)0.1410 M
C)0.2819 M
D)0.0353 M
E)0.0533 M

Question 50

A solution of hydrofluoric acid (0.15 M, 25.00 mL) was titrated with 0.10 M sodium hydroxide (K_a of hydrofluoric acid  7.20  10^4). What is the pH at the equivalence point?

A)5.12
B)6.04
C)7.00
D)7.96
E)8.88

Question 51

Which of the following species is a Lewis acid?

A)Cl₂
B)NH₃
C)F^
D)P(CH₃)₃
E)Al^3

Question 52

A Lewis base is any species capable of ________ an electron pair.

A)accepting
B)donating
C)creating
D)neutralizing
E)gaining

Question 53

A solution of nitrous acid (0.13 M, 20.00 mL) was titrated with 18.0 mL of 0.12 M sodium hydroxide (K_a of nitrous acid  4.00  10^4). What is the final pH of this solution?

A)2.71
B)4.09
C)5.34
D)11.29
E)9.91

Question 54

Vitamin C is a monoprotic weak acid, which also is called ascorbic acid (C₆H₈O₆, 176 g/mol). A vitamin C tablet weighing 0.75 g was dissolved in 50.0 mL of water and titrated with 0.250 M sodium hydroxide. It took 12.5 mL of the NaOH solution to reach the end point. What is the percentage of vitamin C in the tablet? Only the vitamin C reacted with the NaOH.

A)98.7%
B)64.2%
C)87.7%
D)95.5%
E)73.3%

Question 55

In the following reaction, which species is the Lewis acid?

A)Cu^2
B)NH₃
C)[Cu(NH₃)]^2
D)None of these is an acid.
E)All of these are acids.

Question 56

In the following reaction, which species is the Lewis base?

A)Co^2
B)NH₃
C)Co(NH₃)₆^2
D)None of these is a base.
E)All of these are bases.

Question 57

A Lewis base is ________

A)an electron-pair acceptor.
B)an electron-pair donor.
C)a proton donor.
D)a proton acceptor.
E)never viewed also as a Brønsted-Lowry base.

Question 58

A phosphate buffer solution (25.00 mL sample) used for a growth medium was titrated with 0.1000 M hydrochloric acid. The components of the buffer were sodium monohydrogen phosphate and sodium dihydrogen phosphate. The first endpoint occurred at a volume of 10.32 mL; the second occurred after an additional 18.62 mL was added, for a total volume of 28.94 mL. What was the approximate ratio of HPO₄^2 to H₂PO₄^ in the buffer?

A)1:1
B)4:5
C)5:3
D)5:4
E)3:5

Question 59

Which of the following species is a Lewis base?

A)H₃O^
B)Na^
C)BF₃
D)P(CH₃)₃
E)NH₄^

Question 60

A Lewis acid is any species capable of ________ an electron pair.

A)accepting
B)donating
C)creating
D)neutralizing
E)losing

Question 61

The bond between a metal cation and a ligand can best be described as ________

A)an ionic bond.
B)a covalent bond.
C)a coordinate covalent bond.
D)a polar covalent bond.
E)a bidentate bond.

Question 62

Hydrated transition metal ions produce solutions that are ________

A)acidic.
B)basic.
C)neutral.
D)strongly basic.
E)strongly acidic.

Question 63

Determine the molar concentration of Ag^(aq) ions in a 1.00 M solution of AgCl₂^ with no excess chloride. Given: K_f  2.50  10⁵ for AgCl₂^.

A)2.52  10^2 M
B)1.26  10^2 M
C)0.0100 M
D)0.0020 M
E)2.50  10⁵ M

Question 64

Calculate the equilibrium concentration of Zn^2(aq) in a solution that is 0.0125 M Zn(NO₃)₂ and 0.600 M NH₃.
Given: Zn^2(aq)  4NH₃(aq) Zn(NH₃)₄^2(aq) K_f  2.9  10⁹.

A)7.8  10^12 M
B)4.7  10^11 M
C)1.5  10^8 M
D)2.5  10^9 M
E)2.9  10⁹ M

Question 65

Which of the following compounds contains a coordinate covalent bond?

A)Cl₂
B)NH₃
C)H₂CCH₂
D)Co(H₂O)₆^2
E)CH₄

Question 66

When Ni(NH₃)₆Cl₂ dissolves in water, which of the following species form the inner coordination sphere around the Ni^2 ions?

A)other Ni^2 ions
B)Cl^ ions
C)H₂O molecules with O closest to the Ni^2 ions
D)H₂O molecules with H closest to the Ni^2 ions
E)NH₃

Question 67

Which of the following species is most likely to function as a ligand in a transition metal complex ion?

A)BF₄^
B)AlBr₃
C)P(CH₃)₃
D)Ca^2
E)BeCl₂

Question 68

What is the equilibrium concentration of Cu^(aq) in a solution that is 0.0200 M solution in CuNO₃ and 0.450 M HCl(aq)? Given: Cu^(aq)  3Cl^(aq) CuCl₃^2 K_f  5  10⁵.

A)1.0  10^7 M
B)6.7  10^7 M
C)4.4  10^7 M
D)5.0  10^7 M
E)5.0  10⁵ M

Question 69

Which of the following species is least likely to function as a ligand in a transition metal complex ion?

A)NH₄^
B)NH₃
C)Cl^
D)H₂O
E)OH^

Question 70

What is the molar concentration of Ag^(aq) in a 1.00 M solution of Ag(NH₃)₂^ with no excess ammonia? Given: K_f  1.70  10⁷ for Ag (NH₃)₂^.

A)2.45  10^3 M
B)3.09  10^3 M
C)2.42  10^4 M
D)1.47  10^8 M
E)1.70  10^8 M

Question 71

Which statement A-D regarding acids and bases is not correct?

A)A Lewis base is an electron-pair donor; a Lewis acid is an electron-pair acceptor.
B)A Brønsted-Lowry base is a proton acceptor; a Brønsted-Lowry acid is a proton donor.
C)A Lewis base can accept a proton from a Brønsted-Lowry acid.
D)Coordinate covalent bonds in transition metal compounds are formed when a Lewis base reacts with a Lewis acid.
E)Statements A-D are all correct.

Question 72

Which statement A-D regarding a complex ion in a transition metal coordination compound is not correct?

A)The complex ion consists of a metal cation bonded to ligands through coordinate covalent bonds.
B)The ligands in the complex ion are Lewis bases.
C)The ligands are said to occupy the inner coordination sphere.
D)The coordination number is the number of electron pairs bonded to the metal cation.
E)All complex ions have a net positive charge.

Question 73

Many metal cations produce aqueous solutions that have a pH different from 7. Which one of the following statements A-D about this phenomenon is not correct?

A)For a given metal, the cation with the higher oxidation number will produce more acidic solution, for example, Fe^3(aq) is more acidic than Fe^2(aq).
B)The Lewis acidity of the cation is a good measure of its ability to produce an acidic solution.
C)Small highly charged main group metal cations, such as Al^3, produce acidic aqueous solutions.
D)Alkali metal cations, such as Na^ and K^, have a negligible effect on the pH of a solution.
E)Statements A-D are all correct.

Question 74

Determine the molar concentration of Cl^ ions in an equilibrium mixture containing 1.00 M PbCl₄^2 and 0.0010 M Pb^2 ions. Given: K_f  2.5  10¹ for PbCl₄^2.

A)2.51 M
B)1.90 M
C)0.692 M
D)0.628 M
E)0.173 M

Question 75

Lead poisoning used to be treated by injections of ethylenediaminetetraacetic acid, EDTA. If the concentration of EDTA in the blood of a patient is 3.0  10^9 M and the formation constant for Pb(EDTA)^2 is 2.0  10¹⁸, what is the concentration ratio of free toxic Pb^2 to lead-EDTA complex in the blood?

A)2.0  10^11
B)1.7  10^10
C)2.0  10^9
D)5.0  10^19
E)3.0  10^9

Question 76

Which statement A-D regarding transition metal coordination compounds is not correct?

A)A coordination compound is formed when a Lewis acid reacts with a Lewis base.
B)Many, but not all, coordination compounds consist of a complex ion and some number of counter ions.
C)The Lewis bases attached to the metal ion are called ligands.
D)A coordination compound has no net electrical charge.
E)Statements A-D are all correct.

Question 77

A ligand is any ________ forming a coordinate bond to a metal cation.

A)Lewis acid
B)ion
C)Lewis base
D)organic compound
E)species

Question 78

Which of the following compounds contains a coordinate covalent bond?

A)PF₃
B)H₃NBF₃
C)HCOOH
D)AlCl₃
E)O₂

Question 79

A ligand is best described as ________

A)a Lewis acid.
B)a Lewis base.
C)a Brønsted-Lowry acid.
D)a Brønsted-Lowry base.
E)an ion.

Question 80

The bonds between the zinc ion and the nitrogen atoms in the complex Zn(NH₃)₄^2 are best described as ________

A)ionic.
B)covalent.
C)coordinate covalent.
D)polar covalent.
E)d-electron bonds.