Chemistry: An Atoms First Approach
Chemistry: An Atoms First Approach
2nd Edition
ISBN: 9781305079243
Author: Steven S. Zumdahl, Susan A. Zumdahl
Publisher: Cengage Learning
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Chapter 6, Problem 125CP

(a)

Interpretation Introduction

Interpretation: The mass percentage of compound along with balanced chemical equation and formula has to be written.

Concept introduction: The mass percent of compound is given by the calculated mass of the compound to the total mass. The mass percent of compound is given by the formula,

Masspercent(in%)=Calculatedmass(ing)Totalmass(ing)

(a)

Expert Solution
Check Mark

Answer to Problem 125CP

The mass percentage of Cobalt&Chlorine are 29.7%and24.8%

Explanation of Solution

Given:

Record the given info

Mass of sample containing chlorine = 0.256g

Mass of sample containing cobalt    = 0.416g

Mass of silver chloride                     = 0.308g

Mass of cobalt (III) oxide                 = 0.145g

The mass of samples containing chlorine and cobalt are recorded with the masses of silver chloride and cobalt (III) oxide as shown above.

To calculate the mass percent of Cl-

Molar mass of Chlorine          = 35.45g

Molar mass of silver chloride = 143.4g

Moles of Cl- = 0.308gAgCl×35.45gAg143.4gAgCl=0.0761gCl

Therefore, the mass percent of Cl- is,

Mass percent of Cl- = 0.0761g0.256g=29.7%

Mass percent of Cl- = 29.7%

The mass percent of Cl- is calculated by plugging in the values of moles of Cl- to the total mass of sample. The moles of Cl- is calculated by plugging in the values of mass of silver chloride and molar masses of chlorine and silver chloride. The mass percent of Cl- is 29.7%

To calculate the mass percent of Co2+

Molar mass of cobalt                   = 117.86g

Molar mass of cobalt (III) oxide = 165.86g we

Moles of Co2+ = 0.145gCo2O3×117.86gCo165.86gCo2O3=0.103gCo

Therefore, the mass percent of Co2+ is given by,

MasspercentofCo2+=0.103g0.416g×100=24.8%

Mass percent of Co2+ is 24.8%

The mass percent of Co2+ is calculated by plugging in the values of moles of Co2+ to the total mass of sample. The moles of Co2+ is calculated by plugging in the values of mass of silver chloride and molar masses of cobalt and cobalt (III) oxide. The mass percent of cobalt is 24.8% .

To calculate the mass percent of water

Molar mass of water = 18.02g

100-(24.8+27.90)=45.5%iswater

Assume that 100g of compound is,

45.5gH22.016gH18.02gH2O=5.09gHMasspercentofH+=5.09gH100.0g×100=5.09%

45.5gH216.00gO18.02gH2O=40.4gOMasspercentofO-=40.4gO100g×100=40.4%

The mass percent of hydrogen and oxygen is calculated by plugging in the molar mass of water and molar masses of hydrogen and oxygen to the total mass of the sample. The molar masses of hydrogen and oxygen were found to be 5.09% and 40.4%

Conclusion

The mass percentages of Co2+ , Cl- , H+ and O- were calculated using their respective moles and total masses of the samples. The mass percentages of Cl- and Co2+ were found to be 29.7% , 24.8% , 5.09% and 40.4% respectively.

(b)

Interpretation Introduction

Interpretation: To calculate the empirical formula of the compound

Concept introduction: The representation of simplest positive integer of a atoms in a compound is called as empirical formula.

(b)

Expert Solution
Check Mark

Answer to Problem 125CP

The formula for the compound is CoCl2.6H2O

Explanation of Solution

To calculate the empirical formula of the compound

Out of 100 g of compound, there are

24.8gCo×1mol58.93gCo=0.421mol29.7gCl×1mol35.45gCl=0.839mol5.09g1mol1.008gH=5.05mol40.4g1mol16.00gO=2.53mol

Dividing the moles by the smallest number,

The empirical formula of the compound becomes CoCl2.6H2O where, 6H2O the water molecules present in the compound

The empirical formula of the compound is calculated by calculating the mole ratio of individual elements divide by the smallest number. The empirical formula of the compound is found to be CoCl2.6H2O .

Conclusion

The empirical formula of the compound was calculated by using the mole ratio of individual elements divided by the smallest number. The empirical formula of the compound is found to be CoCl2.6H2O .

(c)

Interpretation Introduction

Interpretation: To write the balanced equation of the precipitation reactions.

Concept introduction:

When two solutions containing soluble salts are mixed together, an insoluble salt so called precipitate is obtained and the reaction is called as precipitation reaction. These precipitation reactions help in the determination of various ions in the solution.’

(c)

Expert Solution
Check Mark

Answer to Problem 125CP

CoCl2.6H2O(aq)+2AgNO3(aq)2AgCl(s)+Co(NO3)2(aq)+6H2O(l)CoCl2.6H2O(aq)+2NaOH(aq)Co(OH)2(s)+2NaCl(aq)+6H2O(l)Co(OH)2Co2O34Co(OH)2(s)+O2(g)2Co2O3(s)+4H2O(l)

This is redox reaction. Hence, an oxidizing agent is required and the oxidizing agent is O2

Explanation of Solution

To write the balanced equation of the precipitation reactions.

The reaction between cobalt chloride hexahydrate with base such as silver nitrate and sodium hydroxide yields precipitates of silver chloride and cobalt hydroxide with release of water and sodium chloride. The equation for this reaction can be given as,

CoCl2.6H2O(aq)+AgNO3(aq)AgCl(s)+Co(NO3)2(aq)+H2O(l)CoCl2.6H2O(aq)+NaOH(aq)Co(OH)2(s)+NaCl(aq)+H2O(l)Co(OH)2Co2O3Co(OH)2(s)+O2(g)Co2O3(s)+H2O(l)

Cobalt hydroxide oxidizes to cobalt (III) oxide and water.

Two moles of silver nitrate are required to react with cobalt chloride hexahydrate to give 2 moles of silver chloride as precipitate with side products being cobalt nitrate and water. Cobalt nitrate being water soluble remains inside the solution, thus precipitating silver chloride out of the solution.

Two moles of sodium hydroxide are required to react with cobalt chloride hexahydrate to give 2 moles of cobalt hydroxide with sodium chloride and water. Sodium chloride being soluble in water, dissociates as spectator ions thus remaining in the solution and a precipitate of cobalt hydroxide is precipitated out.

Cobalt hydroxide on heating is oxidized to cobalt (III) oxide with water.

The balanced form of these equations can be given as,

CoCl2.6H2O(aq)+2AgNO3(aq)2AgCl(s)+Co(NO3)2(aq)+6H2O(l)CoCl2.6H2O(aq)+2NaOH(aq)Co(OH)2(s)+2NaCl(aq)+6H2O(l)Co(OH)2Co2O34Co(OH)2(s)+O2(g)2Co2O3(s)+4H2O(l)

The reaction of heating cobalt hydroxide is oxidation-reduction reaction, where oxygen is used as oxidizing agent and cobalt (III) oxide is obtained.

Conclusion

The given reactions were found to be precipitation reaction and moles on the reactant and the product were obtained. The reaction of heating cobalt hydroxide is oxidation-reduction reaction, where oxygen is used as oxidizing agent to oxidized cobalt hydroxide to cobalt (III) oxide. The balanced equations are,

CoCl2.6H2O(aq)+2AgNO3(aq)2AgCl(s)+Co(NO3)2(aq)+6H2O(l)CoCl2.6H2O(aq)+2NaOH(aq)Co(OH)2(s)+2NaCl(aq)+6H2O(l)Co(OH)2Co2O34Co(OH)2(s)+O2(g)2Co2O3(s)+4H2O(l)

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Chapter 6 Solutions

Chemistry: An Atoms First Approach

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