Solubility Equilibrium PDF

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solubility lab...

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Name: Heather Dennis

Partner: Serena Ermond

Student No: 20166876

Student No:

Lab Section: 006

Bench #: 26

Experiment 10: (1 Week) (SOL) Solubility Equilibrium Purpose The purpose of this experiment is to determine identities of unknown anions and cations based on previous observations of reactions between anions and cations (1).

Introduction Reactions can be qualitatively analyzed through changes in colour, pH, or phase. Solubility is the ratio of the maximum amount of solute to the volume of solvent in which the solute can dissolve (2). Solubility equilibrium is the equilibrium associated with dissolving solids in water to form aqueous solution, at the point where no more solid can be dissolve the solution is said to be saturated (3). When two aqueous solutions react sometimes a precipitate, is formed. A precipitate is an insoluble solid that is created when a cation of one reaction and the anion of a second reactant combine in solution (4). A cation is an ion with a net positive change and anion is an ion with a net negative charge (5). To determine if a precipitate is form is based on the solubility of the two reactants. Salts with large Ksp values are very soluble and salts with very small Ksp values will be very insoluble, however, there are exceptions (1).

Procedure 1. Place 10 drops of one cation into four test tubes 2. Place 5 drops of one of the anions into each tube and mix well, recording any observations 3. Repeat step 2 using the remaining anions with the same cation solution, using new cation solution each time 4. Repeat step 2 and 3 with the other cations 5. Place 10 drops of an unknown cation into 4 test tubes 6. Place 5 drops of each anion into a different test tube to identify the unknown cation based on previous observations 7. Place 10 drops of each cation solution into clean test tubes 8. Use an unknown anion and add 5 drops to each test tubes and identify the unknown anion based on previous observations a. Always add anion to cation solution

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Questions 1. Explain in terms of ion concentrations and Ksp why a precipitate form for some solutions. Precipitate forms based on the reactant quotient, Q, and the equilibrium ion concentration, K sp, relationships with each other. If Q ¿ Ksp there is more product present than should be at equilibrium resulting in the solution being supersaturated. The ion concentrations are greater than the equilibrium concentrations resulting in the reaction shifting to the left in the reverse direction resulting in a precipitate forming. If Q ¿ Ksp than there is less product present than should be at equilibrium resulting in the solution being unsaturated. This causes a shift to the right in the forward direction to reach equilibrium resulting in no precipitate forming. If Q=K sp the solution is at equilibrium meaning it is saturated. There is no shift in either direction and no precipitate will form. 2. When ammonia is added to a solution that has Cu (OH) 2(s) precipitate in it, the precipitate dissolves. Use Le Châtelier’s principle to explain this.

The Ksp of Cu(OH)2 is

2.0 ∙10

−19

2+¿ ¿ N H 3 ¿4 ¿ which is relatively low, however the Ksp of is Cu ¿ ¿

13

(7) which is relatively high. As NH3 is added the concentration of the solution increases causing the precipitate to dissolve. According to Le Châtelier’s principle the reaction would proceed in the forward direction because Q ¿ Ksp resulting in more solid dissolving and no new precipitate forming.

1.0 ∙ 10

3. Based on your observations, when a colour change occurs but no phase change occurs, what kind of reaction might have occurred? Based on my observation when there is a colour change, but no phase changes a redox reaction occurred. Colour changes are commonly caused by the oxidation of one compound and the reduction of another (6).

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DATA SHEET

Anions  Cations

0.1 M KI (I–)

1.0 M NH3 (OH–/NH3)

0.1M Na2CO3 (OH–/CO32–)

0.2 M K2CrO4 (CrO4–)

The solution was cloudy and white at the beginning then became dark purple and opaque as the anion fully dissolved.

The solution was dark green and opaque.

No true change, remained light The solution became a cloudy pink and transparent mixture of light blues. As we continued to mix the test tube it became a light blue opaque solution.

The solution was a cloudy pale pink colour. It became opaque as more drops were added and mixed

The solution was orange and translucent.

Copper (II) Very pale cyan blue transparent solution.

The solution because a dark yellow brown colour and was opaque.

The solution became a deeper royal blue tone but not yet navy blue. The solution was opaque.

As the Na2 CO 3 was added the solution began to turn a light shade of sky blue that was darker than original but still very pale. The solution was opaque.

The solution looked similar to the Copper (II) and KI solution, an opaque yellow brown colour, but was darker.

Anions  Cations

0.1 M KI (I–)

1.0 M NH3 (OH–/NH3)

0.1M Na2CO3 (OH–/CO32–)

0.2 M K2CrO4 (CrO4–)

Chromium (III) Light blue, grey, purple colour. Transparent solution.

The solution became a lighter blue grey colour and more transparent version of the original solution.

Cobalt (II) Light pink transparent solution.

The solutions took a long-time mix. As they were mixing the solution was cloudy at first then became a light green blue turquoise colour.

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Iron (III) Transparent

Orange yellow

Difficult to mix substances together, solution became dark orange and opaque with a grainy texture. Darker orange particles settled at the bottom.

Very faint yellow and transparent.

Bright neon orange transparent solution.

Iron (II) Pale transparent yellow solution.

No real colour change stayed very pale colour and transparent

Very dark black green colour. The solution was opaque with black solids forming.

Dark green blue translucent solution.

The solution became a dark muddy brown with precipitate forming at the bottom. The solution was opaque.

Nickel (II)

No real change the solution remained light blue green and transparent.

The solution became blue green but still remained light. It became less transparent but not yet translucent.

The solution became a very light green blue solution, almost white. It was opaque.

The solution became a light lime green yellow colour and was transparent.

Light blue green transparent solution.

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UNKNOWN CATION SAMPLE #: 11 >> IDENTITY? C o 2

+

Reaction with 0.1 M KI

Observations There was no real change, the solution remained light pink and transparent.

Inferences Could potentially be Cobalt (II) because it had the same reaction with KI.

1.0 M NH3

The solution became light blue and opaque.

This cation could be Cobalt (II) because it experienced the same reaction with NH3 and KI above.

0.1 M Na2CO3

The solution became a light cloudy pink and was opaque.

This cation could be Cobalt (II) because it experienced the same reaction with Na2CO3 and NH3, KI above.

0.2 M K2CrO4

The solution became orange and transparent.

This cation could be Cobalt (II) because it experienced the same reaction with K2CrO4 and Na2CO3, NH3, KI above.

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UNKNOWN ANION SAMPLE #: 19 >> IDENTITY? NH3 Reaction with Chromium (III) Light blue, grey, purple colour. Transparent solution.

Observations The solution became a creamy grey, blue, green colour. It was opaque.

Inferences The anion could be NH3 because it experienced the same reaction with Chromium (III).

Cobalt (II) Light pink transparent solution.

The solution became a blue turquoise opaque solution.

The anion could be NH3 because it experienced the same reaction with Cobalt (II) and Chromium (III) above.

Copper (II) Very pale cyan blue transparent solution.

The solution was a very bright royal blue colour was not yet navy, it was opaque.

The anion could be NH3 because it experienced the same reaction with Copper (II) along with Cobalt (II) and Chromium (III) above.

Iron (III)

The solution was a medium orange colour and was opaque with solids forming.

The anion could be NH3 because it experienced the same reaction with Iron (III) in addition to Copper (II), Cobalt (II) and Chromium (III) above.

The solution was dark green, blue, black colour and was opaque.

The anion could be NH3 because it experienced the same reaction with Iron (II) along with Iron (III), Copper (II) Cobalt (II) and Chromium (III) all above.

The solution was a very light blue green solution. It was translucent.

The anion could be NH3 because it experienced the same reaction Nickel (II) as well as Iron (II), Iron (III), Copper (II) Cobalt (II) and Chromium (III) above.

Transparent Iron (II) Pale transparent yellow solution. Nickel (II) Light blue green transparent solution.

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Reaction 1 Type Precipitate Reaction

Net Ionic Equation(s)

2+¿ CO¿

(aq)

+ CO3

(aq)

+ 4 NH 3

2-

(aq)

⟶Co CO 3

(s)

Cobalt (II) and NH3 2 Type Complex Ion Formation (precipitate dissolved)

2+¿ C u¿

(aq)

⟶C u(NH 3)

4

2+

Copper (II) and NH3 3 Type Redox Reaction

3+¿ 2 Fe ¿

(aq)

+ 2I- (aq) ⟶ I 2

(aq)

+

+¿ 2 Fe ¿

(aq)

Iron (III) and KI 4 Type No Reaction

2+¿ Fe¿

(aq)

+ 2I- (aq) ⟶ FeI2 (s)

(aq)

+ CrO 4

Iron (II) and KI 5 Type Redox Reaction

2+¿ ¿¿

2-

(aq)

⟶ NiCrO 4

Note that numbers 1-5 are found in Table 1 in this year’s lab manual.

(aq)

(aq)

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References 1. Chemistry 112 Laboratory Manual 2. Stone, E. (n.d.). Retrieved from https://www.chem.tamu.edu/class/fyp/stone/tutorialnotefiles/acid-base/ksp.htm 3. Chemical Equilibrium - Chemistry. (n.d.). Retrieved from https://www.brightstorm.com/science/chemistry/chemical-equilibrium/

4. What is a Precipitate? (n.d.). Retrieved from https://study.com/academy/lesson/precipitationreactions-predicting-precipitates-and-net-ionic-equations.html

5. Helmenstine, T. (2019, July 3). Do You Know How to Tell Cation and Anion Ions Apart? Retrieved from https://www.thoughtco.com/cation-and-an-anion-differences-606111

6. Helmenstine, A. M. (2019, September 9). Color Change Chameleon Chemistry Demonstration. Retrieved from https://www.thoughtco.com/how-to-do-color-change-chameleon-4057571

7. Wired Chemist. (n.d.). Retrieved from http://www.wiredchemist.com/chemistry/data/solubilityproduct-constants...