Training Skills to Solve Some Inorganic Chemistry Exercises by Using the Graphic Method of Calculati...

C.C. Giac, N.T.P. Lien, P.N. Tuan

World Journal of Chemical Education

Training Skills to Solve Some Inorganic Chemistry Exercises by Using the Graphic Method of Calculation for Teaching Chemistry in High School

C.C. Giac1,, N.T.P. Lien2, P.N. Tuan3

1Faculty of Chemistry, Vinh University, Vinh, Vietnam

2Faculty of Environmental Science, Saigon University, Ho Chi Minh City, Vietnam

3Nguyen Thi Minh Khai High School, Ho Chi Minh City, Vietnam

Abstract

This paper introduces the way to solve some inorganic chemistry exercises by using the graphic method of calculation for teaching chemistry in high school. We have divided them into 7 types of exercise involving in the use of graphs to find the solution methods. Based on these ways, the authors have built 9 Sample Problems. On that basis, the authors compiled 15 drilling exercises for Test Yourself which are used for teaching and self-studying inorganic chemistry in High School.

Cite this article:

  • C.C. Giac, N.T.P. Lien, P.N. Tuan. Training Skills to Solve Some Inorganic Chemistry Exercises by Using the Graphic Method of Calculation for Teaching Chemistry in High School. World Journal of Chemical Education. Vol. 5, No. 1, 2017, pp 12-19. http://pubs.sciepub.com/wjce/5/1/3
  • Giac, C.C., N.T.P. Lien, and P.N. Tuan. "Training Skills to Solve Some Inorganic Chemistry Exercises by Using the Graphic Method of Calculation for Teaching Chemistry in High School." World Journal of Chemical Education 5.1 (2017): 12-19.
  • Giac, C. , Lien, N. , & Tuan, P. (2017). Training Skills to Solve Some Inorganic Chemistry Exercises by Using the Graphic Method of Calculation for Teaching Chemistry in High School. World Journal of Chemical Education, 5(1), 12-19.
  • Giac, C.C., N.T.P. Lien, and P.N. Tuan. "Training Skills to Solve Some Inorganic Chemistry Exercises by Using the Graphic Method of Calculation for Teaching Chemistry in High School." World Journal of Chemical Education 5, no. 1 (2017): 12-19.

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At a glance: Figures

1. Introduction

Chemistry exercises play an important role, including content and chemistry teaching methods in high school. Training skills to solve problems is indispensable in chemistry teaching activities. Within the scope of this paper, we will introduce some types of inorganic chemistry exercises that use graphs to infer solution methods. Thereby, training and enhancing skills to solve chemistry exercises in general and inorganic chemistry in particular is very important for students [1, 2, 3].

2. Content

2.1. General Problem

In inorganic chemistry, a common problem is

(The symbol P↓ stands for “precipitate” in solution).

The precipitate P can be soluble in an excess reactant of A or B. At that time the same amount of precipitate can have two different values of A or B. To solve this problems, teacher can guide students to use the graph of the relationship between the number of moles of precipitate P ( ) and the number of moles of A or B [4, 5].

2.2. Some Common Types
2.2.1. Type 1: Bubble Slowly the Gas of CO2 or SO2 through Solution of Ca(OH)2 or Ba(OH)2 → P↓ Soluble

In this case CO2 will perform 2 tasks below.

Task 1: Increase gradually the mass of precipitate up to a maximum, according to the reaction

(1)

Task 2: Dissolve the precipitate, according to the reaction

(2)

The relationship between the number of moles of CO2 and the number of moles of precipitate is represented as the graph in Figure 1.


2.2.2. Type 2: Bubble slowly the Gas of CO2 or SO2 Through the Mixture Solution of Ca(OH)2/Ba(OH)2 and NaOH/KOH → P↓ Soluble

In this case CO2 will perform 3 tasks below.

Task 1: Form the maximum mass of precipitate, according to the reaction

(1)

Task 2: React between acidic oxide with alkali to form the acidic salt (not neutral salt because of excess CO2), according to the reaction

(2)

Task 3: Dissolve the precipitate, according to the reaction

(3)

The relationship between the number of moles of CO2 and the number of moles of precipitate is represented by the graph in Figure 2.


2.2.3. Type 3: Add Slowly Solution of NaOH to Solution of Al3+/Zn2+ P Soluble

In this case OH- will perform 2 tasks below.

Task 1: Form the maximum mass of precipitate, according to the reaction

(1)

Task 2: Dissolve the precipitate, according to the reaction

(2)

The relationship between the number of moles of OH- and the number of moles of precipitate is represented by the graph in Figure 3.


2.2.4. Type 4: Add Slowly Solution of NaOH to Mixture Solution of Al3+/Zn2+ and H+ P Soluble

In this case OH- will perform 3 tasks below.

Task 1: Neutralize H+ ion in the solution, according to the reaction

(1)

Task 2: Form the maximum mass of precipitate, according to the reaction

(2)

Task 3: Dissolve the precipitate, according to the reaction

(3)

The relationship between the number of moles of OH- and the number of moles of precipitate is represented by the graph in Figure 4.


2.2.5. Type 5: Add Slowly Solution of HCl to the Solution of [Al(OH)4]- / [Zn(OH)4]2- P Soluble

In this case H+ will perform 2 tasks below

Task 1: Form the maximum mass of precipitate, according to the reaction

(1)

Task 2: Dissolve the precipitate, according to the reaction

(2)

The relationship between the number of moles of H+ and the number of moles of precipitate is represented by the graph in Figure 5.


2.2.6. Type 6: Add Slowly Solution of HCl to the Mixture Solution of [Al(OH)4]- / [Zn(OH)4]2- and OH- P Soluble

In this case H+ will perform 3 tasks below.

Task 1: Neutralize OH- ion in the solution, according to the reaction

(1)

Task 2: React between H+ ion with complex ion to form the precipitate, according to the reaction

(2)

Task 3: Dissolve the precipitate, according to the reaction

(3)

The relationship between the number of moles of H+ ion and the number of moles of precipitate is represented by the graph in Figure 6.


2.2.7. Type 7: Add Slowly Solution of NH3 to the Solution of Cu2+/Cu1+/Zn2+/Ag+ P Soluble

In this case NH3 will perform 2 tasks below.

Task 1: Form the maximum mass of precipitate, according to the reaction

(1)

Task 2: Dissolve the precipitate, according to the reaction

(2)

The relationship between the number of moles of NH3 and the number of moles of precipitate Cu(OH)2 is represented by the graph in Figure 7.

2.3. Sample Problems

Based on the 7 types of common exercise above, we designed some following exercises to help students practising skills using graphs to solve the exercises of inorganic chemistry in high school.

Example 1: Bubble slowly the gas of CO2 through mixture solution of Ca(OH)2 and KOH. Observed the phenomena according to the following graph (data are calculated in units of moles).

The value of x is

A. 0.45B. 0.42

C. 0.48D. 0.60

Solution: Based on the above graph, we can see the order of tasks of CO2 is

Task 1:

Task 2:

(do not form the neutral salt because of the excess carbon dioxide which dissolved the precipitate)

Task 3:

At the position at which = 3 = a + a + a a = 1 x = 0.6a = 0.6 Answer D.

Example 2: Add slowly an excess of NaOH solution to AlCl3 solution. Experimental results are shown in the following graph (data are calculated in units of moles)

The value of x is

A. 0.412B. 0.456

C. 0.51  D. 0.546

Solution: From the graph, we find that

At the position at which

Answer B.

Example 3: Add slowly 0.2 M Ba(OH)2 solution to a test tube containing V (L) of c (mol/l) Al2(SO4)3 solution. Experimental results are shown in the following graph

When the mass of precipitate is a constant, the minimum volume of Ba(OH)2 solution is required to be

A. 30 mLB. 60 mL

C. 45 mLD. 75 mL

Solution: From the graph, we find that OH- ion performed 2 tasks below

Task 1: Increase gradually the mass of precipitate up to a maximum.

Task 2: Dissolve the precipitate.

In which parallel segment to the axis shown that BaSO4 precipitate is insoluble in base.

We find that :

and

Answer B.

Example 4: Add slowly an excess of NaOH solution to the mixture of solution containing a mol HCl and b mol AlCl3. Experimental results are shown in the following graph (data are calculated in units of moles)

The ratio of is

A. 4/3B. 2/3

C. 1/1D. 2/1

Solution: From the graph, we find that OH- ion performed 3 tasks below.

Task 1: Neutralize the acid in that solution

Task 2: Increase gradually the mass of precipitate up to a maximum

Task 3 : Dissolve the precipitate

At the position at which

The ratio = Answer A.

Example 5: Add slowly an excess of HCl solution to the mixture of solution containing x mol Ba(OH)2 and y mol Ba[Al(OH)4]2. Experimental results are shown in the following graph (data are calculated in units of moles).

The value of x and y are

A. 0.05 and 0.15B. 0.10 and 0.30

C. 0.10 and 0.15D. 0.05 and 0.30

Solution: From the graph, we find that H+ ion performed 3 tasks below.

Task 1: Neutralize the base in that solution

Task 2: Increase gradually the mass of precipitate up to a maximum

Task 3 : Dissolve the precipitate

At the position at which

Answer A.

Example 6: Add slowly an excess of HCl solution to the mixture of solution containing a mol KOH and b mol K2[Zn(OH)4]. Experimental results are shown in the following graph (data are calculated in units of moles).

The ratio of is

A. 1.5B. 1.0

C. 2.0D. 2.5

Solution: From the graph, we find that H+ ion performed 3 tasks below.

Task 1: Neutralize the base in that solution

Task 2: Increase gradually the mass of precipitate up to a maximum

Task 3: Dissolve the precipitate

At the position at which

= Answer C.

Example 7: Add slowly an excess of NaOH solution to the mixture of solution containing a mol HCl and b mol ZnCl2. Experimental results are shown in the following graph (data are calculated in units of moles)

The total value of (a + b) is

A. 1.4B. 1.6

C. 1.2D. 1.3

Solution: From the graph, we find that OH- ion performed 3 tasks below.

Task 1: Neutralize the acid in that solution

Task 2: Increase gradually the mass of precipitate up to a maximum

Task 3: Dissolve the precipitate

At the position at which

Answer C.

Example 8: Add slowly an excess of NaOH solution to AlCl3 solution, experimental results are shown in the following graph (data are calculated in units of moles)

The ratio of is

A. 7/8B. 6/7

C. 5/4D. 4/5

Solution: From the graph, we find that OH- ion performed 2 tasks below.

Task 1: Increase gradually the mass of precipitate up to a maximum

Task 2: Dissolve the precipitate

From the graph, we find that

Answer B.

Example 9: Bubble slowly the gas of CO2 through mixture solution of Ca(OH)2 and NaOH. Experimental results are shown in the following graph (data are calculated in units of moles)

The value of x is

A. 0.64B. 0.58

C. 0.68D. 0.62

Solution: From the graph, we find that CO2 performed 3 tasks below.

Task 1: Increase gradually the mass of precipitate up to a maximum

Task 2: Keep the constant mass of precipitate

Task 3: Dissolve the precipitate

We have: Answer A.

2.4. Test Yourself

1. Bubble slowly the gas of CO2 through solution of Ba(OH)2. Observed the phenomena happening according to the following graph (data are calculated in units of moles)

The value of x is

A. 1.8B. 2.0

C. 2.2D. 2.4

Answer B

2. Bubble slowly V (L) at s.t.p. of the gas of CO2 through the mixture of Ba(OH)2 and KOH solution. Experimental results are shown in the following graph (data are calculated in units of moles). Hint: 1 mole of gas at s.t.p. occupies 22.4 dm3.

In order to obtain the maximum precipitate, the value of V is

A. 4.480 V 8.960B. 2.240 V 6.720

C. 3.654 V 6.585D. 4.200 V 8.904

Answer D

3. Add slowly an excess of NaOH solution to AlCl3 solution. Experimental results are shown in the following graph (data are calculated in units of moles)

The value of x is

A. 0.412B. 0.456

C. 0.515D. 0.546

Answer B

4. Add slowly an excess of NaOH solution to the mixture of solution containing a mol HCl and b mol AlCl3. Experimental results are shown in the following graph (data are calculated in units of moles)

The ratio of  is

A. 4/3B. 2/3

C. 1/1D. 2/1

Answer A

5. Add slowly an excess of HCl solution to the mixture of solution containing x mol Ba(OH)2 and y mol Ba[Al(OH)4]2. Experimental results are shown in the following graph (data are calculated in units of moles)

The value of x and y are

A. 0.05 và 0.15B. 0.10 và 0.30

C. 0.10 và 0.15D. 0.05 và 0.30

Answer A

6. Add slowly 0.2 M Ba(OH)2 solution to a test tube containing V (L) of c (mol/l) ZnSO4 solution. Experimental results are shown in the following graph

In order to constant precipitate, the volume of Ba(OH)2 solution is the minimum needed

A. 50 mLB. 60 mL

C. 45 mLD. 75 mL

Answer D

7. Add slowly an excess of NaOH solution to X solution containing x mol H2SO4 and y mol Al2(SO4)3. Experimental results are shown in the following graph (data are calculated in units of moles)

If add slowly a solution containing 0.7 mol Ba(OH)2 to solution X until the reaction occurs completely, we obtain m grams of precipitate. Value of m is closest to which of the following value?

A. 170B. 150

C. 180D. 120

Answer A

8. Add slowly an excess of X solution to Y solution to form Z precipitate. Experimental results are shown in the following graph (data are calculated in units of moles)

Which result of the following experiment is shown as the above graph?

A. Add slowly an excess of HCl solution to Na[Al(OH)4] solution

B. Add slowly an excess of NaOH solution to AlCl3 solution

C. Add slowly an excess of NaOH solution to ZnCl2 solution

D. Bubble slowly the gas of CO2 through solution of Ca(OH)2

Answer A

9. When add slowly a substance X to a substance Y to form a precipitate Z. Experimental results are shown in the following graph (data are calculated in units of moles)

Which result of the following experiment is shown as the graph above?

A. Add slowly an excess of HCl solution to Na[Al(OH)4] solution

B. Add slowly an excess of NaOH solution to AlCl3 solution

C. Add slowly an excess of HCl solution to Na2[Zn(OH)4] solution

D. Bubble slowly the gas of CO2 through solution of Ca(OH)2

Answer B

10. Add slowly a substance X to a substance Y to form a precipitate Z. Experimental results are shown in the following graph (data are calculated in units of moles)

Which result of the following experiment is shown as the above graph?

A. Add slowly an excess of KOH solution to ZnCl2 solution

B. Bubble slowly the gas of CO2 through solution of Ca(OH)2

C. Bubble slowly the gas of NH3 through solution of AlCl3

D. Bubble slowly the gas of NH3 through solution of ZnCl2

Answer C

11. Add slowly an excess of X solution to Y solution to form Z precipitate. Experimental results are shown in the following graph (data are calculated in units of moles)

Which result of the following experiment is shown as the graph above?

A. Add slowly an excess of Ba(OH)2 solution to AlCl3 solution

B. Add slowly an excess of Ba(OH)2 solution to Al2(SO4)3 solution

C. Add slowly an excess of Ba(OH)2 solution to mixture solution of HCl and AlCl3

D. Add slowly an excess of NaOH solution to Al2(SO4)3 solution

Answer B

12. Dissolve AlCl3 in water to form a solution X. Add slowly an excess of NaOH solution to X solution. Experimental results are shown in the following graph.

Based on the above graph, the maximum mass of the precipitate obtained in above experiment is

A. 12.48 gramsB. 14.04 grams

C. 16.77 gramsD. 23.40 grams

Answer C

13. A solution X contains a mol of ZnSO4, a solution Y contains b mol of AlCl3 and a solution Z contains c mol of KOH. Perform 2 following experiments:

Experiment 1: Add slowly to the end of an excess of the solution Z to the solution X.

Experiment 2: Add slowly to the end of an excess of the solution Z to the solution Y.

The precipitate of two experiments changed according to the following graph

If each experiment used x mol KOH, the total mass (grams) precipitate obtained in two experiments will be closest to which of the following value?

A. 8.0B. 8.5

C. 9.0D. 9.5

Answer B

14. Bubble slowly the gas of CO2 through 11 % (by mass) Ca(OH)2 solution. The reaction occurs completely to form a solution X. Experimental results are shown in the following graph (data are calculated in units of moles)

Defining concentration of solution X in terms of mass percent?

A. 16.20 %B.14.59 %

C. 15.28 %D. 16.87 %

Answer C

15. Dissolve a mixture X containing a mol K and b mol Ca in 200 mL 0.1 M Ca(OH)2 solution to form the solution Y and V (L) the gas of H2 (at s.t.p.). Bubble slowly an excess of CO2 gas through Y solution. Experimental results are shown in the following graph (data are calculated in units of moles). Hint: 1 mol of gas at s.t.p. occupies 22.4 dm3.

The value of V is

A. 14.56B. 19.04

C. 22.40D. 26.88

Answer A

3. Conclusions

The paper proposed identification signs of 7 types of inorganic chemistry exercises can use the graphic method to solve easily. Based on the experimental results are shown in the graph, easily infer the relationship between the number of moles of precipitate and the number of moles of reactants. Thereby, teacher will practice skills to solve chemical exercises for students based on the experimental results are illustrated by the graph. They are exciting forms of exercise for students in high school.

Acknowledgements

We thank the anonymous reviewers of this paper for many very helpful suggestions.

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