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Iron(II) can be oxidized to iron(III) by dichromate ion, which is reduced to chromium(III) in acid solution. A 2.5000-g sample of iron ore is dissolved and the iron converted into iron(II). Exactly 19.17 mL of 0.0100 M Na 2 Cr 2 O 7 is required in the titration. What percentage of the ore sample was iron?

2.57%

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How many cubic feet of air at a pressure of 760 torr and 0 °C is required per ton of Fe 2 O 3 to convert that Fe 2 O 3 into iron in a blast furnace? For this exercise, assume air is 19% oxygen by volume.

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Find the potentials of the following electrochemical cell:

Cd | Cd 2+ , M = 0.10 ‖ Ni 2+ , M = 0.50 | Ni

0.167 V

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A 2.5624-g sample of a pure solid alkali metal chloride is dissolved in water and treated with excess silver nitrate. The resulting precipitate, filtered and dried, weighs 3.03707 g. What was the percent by mass of chloride ion in the original compound? What is the identity of the salt?

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The standard reduction potential for the reaction [ Co ( H 2 O ) 6 ] 3+ ( a q ) + e [ Co ( H 2 O ) 6 ] 2+ ( a q ) is about 1.8 V. The reduction potential for the reaction [ Co ( NH 3 ) 6 ] 3+ ( a q ) + e [ Co ( NH 3 ) 6 ] 2+ ( a q ) is +0.1 V. Calculate the cell potentials to show whether the complex ions, [Co(H 2 O) 6 ] 2+ and/or [Co(NH 3 ) 6 ] 2+ , can be oxidized to the corresponding cobalt(III) complex by oxygen.

E ° = −0.6 V, E ° is negative so this reduction is not spontaneous. E ° = +1.1 V

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Predict the products of each of the following reactions. (Note: In addition to using the information in this chapter, also use the knowledge you have accumulated at this stage of your study, including information on the prediction of reaction products.)

(a) MnCO 3 ( s ) + HI ( a q )

(b) CoO ( s ) + O 2 ( g )

(c) La ( s ) + O 2 ( g )

(d) V ( s ) + VCl 4 ( s )

(e) Co ( s ) + x s F 2 ( g )

(f) CrO 3 ( s ) + CsOH ( a q )

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Predict the products of each of the following reactions. (Note: In addition to using the information in this chapter, also use the knowledge you have accumulated at this stage of your study, including information on the prediction of reaction products.)

(a) Fe ( s ) + H 2 SO 4 ( a q )

(b) FeCl 3 ( a q ) + NaOH ( a q )

(c) Mn ( OH ) 2 ( s ) + HBr ( a q )

(d) Cr ( s ) + O 2 ( g )

(e) Mn 2 O 3 ( s ) + HCl ( a q )

(f) Ti ( s ) + x s F 2 ( g )

(a) Fe ( s ) + 2 H 3 O + ( a q ) + SO 4 2− ( a q ) Fe 2+ ( a q ) + SO 4 2− ( a q ) + H 2 ( g ) + 2 H 2 O ( l ) ; (b) FeCl 3 ( a q ) + 3Na + ( a q ) + 3OH ( a q ) Fe ( OH ) 3 ( s ) + 3Na + ( a q ) + 3Cl + ( a q ) ; (c) Mn ( OH ) 2 ( s ) + 2 H 3 O + ( a q ) + 2Br ( a q ) Mn 2+ ( a q ) + 2Br ( a q ) + 4 H 2 O ( l ) ; (d) 4Cr ( s ) + 3 O 2 ( g ) 2 Cr 2 O 3 ( s ) ; (e) Mn 2 O 3 ( s ) + 6 H 3 O + ( a q ) + 6Cl ( a q ) 2 MnCl 3 ( s ) + 9 H 2 O ( l ) ; (f) Ti ( s ) + x s F 2 ( g ) TiF 4 ( g )

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Describe the electrolytic process for refining copper.

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Predict the products of the following reactions and balance the equations.

(a) Zn is added to a solution of Cr 2 (SO 4 ) 3 in acid.

(b) FeCl 2 is added to a solution containing an excess of Cr 2 O 7 2− in hydrochloric acid.

(c) Cr 2+ is added to Cr 2 O 7 2− in acid solution.

(d) Mn is heated with CrO 3 .

(e) CrO is added to 2HNO 3 in water.

(f) FeCl 3 is added to an aqueous solution of NaOH.

(a)
Cr 2 ( SO 4 ) 3 ( a q ) + 2Zn ( s ) + 2H 3 O + ( a q ) 2Zn 2+ ( a q ) + H 2 ( g ) + 2H 2 O ( l ) + 2Cr 2+ ( a q ) + 3SO 4 2− ( a q ) ; (b) 4TiCl 3 ( s ) + CrO 4 2− ( a q ) + 8H + ( a q ) 4Ti 4+ ( a q ) + Cr ( s ) + 4H 2 O ( l ) + 12Cl ( a q ) ; (c) In acid solution between pH 2 and pH 6, CrO 4 2− forms HCrO 4 , which is in equilibrium with dichromate ion. The reaction is 2HCrO 4 ( a q ) Cr 2 O 7 2− ( a q ) + H 2 O ( l ) . At other acidic pHs, the reaction is 3Cr 2+ ( a q ) + CrO 4 2− ( a q ) + 8H 3 O + ( a q ) 4Cr 3+ ( a q ) + 12H 2 O ( l ) ; (d) 8CrO 3 ( s ) + 9Mn ( s ) Δ 4Cr 2 O 3 ( s ) + 3Mn 3 O 4 ( s ) ; (e) CrO ( s ) + 2H 3 O + ( a q ) + 2NO 3 ( a q ) Cr 2+ ( a q ) + 2NO 3 ( a q ) + 3H 2 O ( l ) ; (f) CrCl 3 ( s ) + 3NaOH ( a q ) Cr ( OH ) 3 ( s ) + 3Na + ( a q ) + 3Cl ( a q )

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What is the gas produced when iron(II) sulfide is treated with a nonoxidizing acid?

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Predict the products of each of the following reactions and then balance the chemical equations.

(a) Fe is heated in an atmosphere of steam.

(b) NaOH is added to a solution of Fe(NO 3 ) 3 .

(c) FeSO 4 is added to an acidic solution of KMnO 4 .

(d) Fe is added to a dilute solution of H 2 SO 4 .

(e) A solution of Fe(NO 3 ) 2 and HNO 3 is allowed to stand in air.

(f) FeCO 3 is added to a solution of HClO 4 .

(g) Fe is heated in air.

(a) 3Fe ( s ) + 4H 2 O ( g ) Fe 3 O 4 ( s ) + 4H 2 ( g ) ; (b) 3NaOH ( a q ) + Fe ( NO 3 ) 3 ( a q ) H 2 O Fe ( OH ) 3 ( s ) + 3Na + ( a q ) + 3 NO 3 ( a q ) ; (c) MnO 4− + 5 Fe 2+ + 8 H + Mn 2+ + 5 Fe 3 + 4 H 2 O ; (d) Fe ( s ) + 2H 3 O + ( a q ) + SO 4 2− ( a q ) Fe 2+ ( a q ) + SO 4 2− ( a q ) + H 2 ( g ) + 2H 2 O ( l ) ; (e) 4Fe 2+ ( a q ) + O 2 ( g ) + 4HNO 3 ( a q ) 4Fe 3+ ( a q ) + 2H 2 O ( l ) + 4NO 3 ( a q ) ; (f) FeCO 3 ( s ) + 2HClO 4 ( a q ) Fe ( ClO 4 ) 2 ( a q ) + H 2 O ( l ) + CO 2 ( g ) ; (g) 3Fe ( s ) + 2O 2 ( g ) Δ Fe 3 O 4 ( s )

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Balance the following equations by oxidation-reduction methods; note that three elements change oxidation state.
Co ( NO 3 ) 2 ( s ) Co 2 O 3 ( s ) + NO 2 ( g ) + O 2 ( g )

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Dilute sodium cyanide solution is slowly dripped into a slowly stirred silver nitrate solution. A white precipitate forms temporarily but dissolves as the addition of sodium cyanide continues. Use chemical equations to explain this observation. Silver cyanide is similar to silver chloride in its solubility.

As CN is added,
Ag + ( a q ) + CN ( a q ) AgCN ( s )
As more CN is added,
Ag + ( a q ) + 2 CN ( a q ) [ Ag (CN) 2 ] ( a q ) AgCN ( s ) + CN ( a q ) [ Ag (CN) 2 ] ( a q )

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Predict which will be more stable, [CrO 4 ] 2− or [WO 4 ] 2− , and explain.

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Give the oxidation state of the metal for each of the following oxides of the first transition series. (Hint: Oxides of formula M 3 O 4 are examples of mixed valence compounds in which the metal ion is present in more than one oxidation state. It is possible to write these compound formulas in the equivalent format MO·M 2 O 3 , to permit estimation of the metal’s two oxidation states.)

(a) Sc 2 O 3

(b) TiO 2

(c) V 2 O 5

(d) CrO 3

(e) MnO 2

(f) Fe 3 O 4

(g) Co 3 O 4

(h) NiO

(i) Cu 2 O

(a) Sc 3+ ; (b) Ti 4+ ; (c) V 5+ ; (d) Cr 6+ ; (e) Mn 4+ ; (f) Fe 2+ and Fe 3+ ; (g) Co 2+ and Co 3+ ; (h) Ni 2+ ; (i) Cu +

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Source:  OpenStax, Chemistry. OpenStax CNX. May 20, 2015 Download for free at http://legacy.cnx.org/content/col11760/1.9
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