kelarutan Dan Hasil Kali kelarutan (2) | Pengaruh Ion Sejenis atau Senama | Kimia kelas 11

Summary

This video lesson explores the solubility and solubility product (Ksp) concepts for Class 11 Chemistry, focusing on the effect of common ions on solubility. It explains how the presence of ions identical to those in a salt reduces its solubility, following Le Chatelier's principle. Through worked examples, including PbI₂ in pure water, Pb(NO₃)₂, and AgNO₃ solutions, as well as AgBr in MgBr₂, the video demonstrates step-by-step calculations of solubility changes. It also covers Mg(OH)₂ solubility in various solutions, highlighting that lower concentrations of common ions lead to higher solubility. The lesson emphasizes clear methods for applying Ksp to predict and calculate solubility in different chemical contexts.

Takeaways

• 😀 The video explains the concept of solubility and the solubility product (Ksp) for Class 11 Chemistry students.
• 😀 The presence of a common ion (ion sejenis) decreases the solubility of a salt due to Le Chatelier's principle.
• 😀 For AgCl, adding extra Ag⁺ or Cl⁻ ions shifts the equilibrium to the left, increasing precipitation and reducing solubility.
• 😀 The solubility (s) of a salt in pure water can be calculated using the relationship Ksp = [cation][anion]^n based on the dissociation reaction.
• 😀 Example calculation: PbI₂ solubility in pure water is 1.6 × 10⁻³ M, using the formula 4s³ = Ksp.
• 😀 Solubility decreases significantly when the salt is dissolved in a solution already containing a common ion, e.g., Pb(NO₃)₂ or AgI solution.
• 😀 When calculating solubility in a solution with a common ion, the small contribution from the salt itself can often be ignored compared to the pre-existing ion concentration.
• 😀 The video demonstrates similar calculations for AgBr in MgBr₂ solution, showing drastically reduced solubility due to the common Br⁻ ion.
• 😀 To find the highest solubility of a salt like Mg(OH)₂, select the solution with the lowest concentration of the common ion OH⁻.
• 😀 Overall, understanding ion effects and Ksp calculations helps predict solubility behavior in different solutions and explains precipitation tendencies.

Q & A

What is the effect of adding a common ion to a solution on the solubility of a salt?

Adding a common ion (an ion already present in the solution that is part of the salt) decreases the solubility of the salt. This occurs because the equilibrium shifts toward the solid form according to Le Chatelier's principle.

How does Le Chatelier's principle explain the common ion effect?

Le Chatelier's principle states that a system at equilibrium will adjust to counteract a change. When a common ion is added, the solution shifts the equilibrium toward forming more solid precipitate, thereby reducing the solubility of the salt.

What is the solubility product constant (Ksp) and how is it used?

Ksp is an equilibrium constant representing the maximum amount of a salt that can dissolve in a solution. It is used to calculate the solubility of ionic compounds in pure water or in solutions containing common ions.

How do you calculate the solubility of PbI2 in pure water using Ksp?

For PbI2, which dissociates as PbI2 ⇌ Pb²⁺ + 2 I⁻, the solubility s can be found using Ksp = [Pb²⁺][I⁻]² = s(2s)² = 4s³. Solving for s gives s = (Ksp/4)^(1/3).

What is the solubility of PbI2 in a solution containing 0.1 M Pb(NO3)2?

The solubility decreases due to the common ion effect from Pb²⁺. Using Ksp = [Pb²⁺][I⁻]² ≈ 0.1 × (2s)², the solubility s is calculated as 2 × 10⁻⁴ M.

Why does PbI2 have much lower solubility in a solution containing AgNO3?

AgNO3 introduces a common ion I⁻. The presence of this additional I⁻ shifts the equilibrium toward forming solid PbI2, greatly reducing its solubility to 4 × 10⁻⁷ M.

How is the solubility of AgBr in MgBr2 solution affected by the common ion?

MgBr2 provides Br⁻ ions, which are common to AgBr. This reduces the solubility drastically. For example, with 0.25 M MgBr2, the solubility of AgBr drops to 9.8 × 10⁻¹³ M.

How can you identify which solution will give the highest solubility for Mg(OH)2?

The highest solubility occurs in the solution with the lowest concentration of OH⁻ ions because OH⁻ is the common ion. Less OH⁻ means less suppression of Mg(OH)2 solubility.

Why is the solubility of a salt smaller in a solution containing a common ion compared to pure water?

Because the added common ion increases the concentration of one of the ions already in equilibrium, the system shifts toward precipitating more solid, which decreases the amount of salt that can dissolve.

How do you adjust the solubility formula for salts in solutions with common ions?

In solutions with common ions, the total ion concentration is the sum of the contribution from the salt's dissolution and the existing common ion. Often, the existing ion dominates, and the contribution from the solubility can be approximated as negligible.

What general trend can be concluded about the effect of ion concentration on solubility?

As the concentration of a common ion increases, the solubility of the corresponding salt decreases. Conversely, solubility is highest when the concentration of common ions is lowest.

Can the common ion effect be used to selectively precipitate salts?

Yes, by adding a solution that contains a common ion, you can decrease the solubility of a specific salt, causing it to precipitate while other salts remain in solution.