Hidrolisis Garam (2) | Penentuan pH Larutan Garam| Kimia Kelas 11

Summary

In this video, the presenter explains the concept of salt hydrolysis and how to determine the pH of salt solutions. The explanation covers four types of salts formed from different combinations of strong and weak acids and bases, detailing their acidic, basic, or neutral properties. The video also demonstrates how to calculate pH using specific formulas, with examples including salts like KCl, NH4SO4, and CH3COONa. It further explores how to solve pH problems directly and indirectly using data from acids and bases, providing clear, step-by-step instructions for determining pH in various scenarios.

Takeaways

• 😀 Garam can be categorized into four types based on the acid and base from which they are formed: 1) salt from strong acid and strong base (neutral), 2) salt from strong acid and weak base (acidic), 3) salt from weak acid and strong base (basic), and 4) salt from weak acid and weak base (depends on Ka and Kb).
• 😀 For salts formed from a strong acid and a strong base (e.g., KCl), the pH is neutral (pH = 7).
• 😀 Salts formed from a strong acid and a weak base (e.g., NH4Cl) are acidic with a pH less than 7. The pH can be calculated using a specific formula involving K_w, K_b, and the concentration of the salt.
• 😀 For salts formed from a weak acid and a strong base (e.g., CH3COONa), the pH is basic (greater than 7), and the pH can be determined using a similar formula involving K_w, K_a, and the concentration of the salt.
• 😀 Salts formed from weak acids and weak bases exhibit variable pH values depending on the relative strength of Ka and Kb. If Ka > Kb, the pH will be acidic; if Ka < Kb, the pH will be basic; if Ka = Kb, the pH will be neutral.
• 😀 To calculate the pH of a salt solution, you can use the formulas: for acidic salts, [H+] = √(K_w / K_b) × concentration × X, and for basic salts, [OH-] = √(K_w / K_a) × concentration × X, where X represents the number of ions from the weak acid or base.
• 😀 In practical applications, the pH can be determined directly by plugging in known values for K_w, K_a, K_b, and concentration, as shown in sample problems involving salts like CaCO3 and NH4Cl.
• 😀 A direct example of using the pH calculation formula: for a solution of CaCO3, the pH is determined based on the concentration of the salt and the specific ion contributions from its weak acid and strong base components.
• 😀 For NH4Cl (which is acidic), the pH is calculated by determining the concentration of H+ ions through the formula and solving for the final pH value.
• 😀 In some cases, when the reactants are known (e.g., H2SO4 and NH4OH), the pH of the resulting salt solution can be determined indirectly by first finding the limiting reagent, calculating the moles, and determining the final concentration of the salt formed (NH4)2SO4. This value can then be used to calculate the pH of the solution.

Q & A

What is the main topic of the video?

The main topic of the video is about learning how to determine the pH of salt solutions, specifically focusing on hydrolysis of salts in chemistry for 11th grade students.

What are the four types of salts based on the acid-base composition?

The four types of salts are: 1) Salt from a strong acid and a strong base (neutral, pH = 7), 2) Salt from a strong acid and a weak base (acidic, pH < 7), 3) Salt from a weak acid and a strong base (basic, pH > 7), and 4) Salt from a weak acid and a weak base (pH depends on the strengths of Ka and Kb).

How is the pH of a salt formed from a strong acid and a weak base determined?

The pH of such a salt is acidic, and the pH can be determined using the formula: [H+] = √(Kw / Kb × salt concentration × X), where X is the number of ions from the weak base.

Can you give an example of a salt formed from a strong acid and a weak base?

An example of a salt formed from a strong acid and a weak base is ammonium sulfate (NH4)2SO4.

What formula is used to determine the pH of a salt formed from a weak acid and a strong base?

For such salts, the formula used to determine the pH is: [OH-] = √(Kw / Ka × salt concentration × X), where X represents the number of ions from the weak acid.

Provide an example of a salt formed from a weak acid and a strong base.

An example of a salt formed from a weak acid and a strong base is sodium acetate (CH3COONa).

What happens when a salt is formed from both a weak acid and a weak base?

The pH of such salts depends on the relative values of Ka and Kb. If Ka > Kb, the salt will be acidic. If Ka < Kb, the salt will be basic. If Ka = Kb, the salt will be neutral.

What is the method to determine pH for salt solutions where the acid and base data are provided?

When acid and base data are provided, the pH is determined through indirect calculation. First, the acid and base must fully react, and the stoichiometric ratio of their moles is considered. The pH is then determined from the resulting salt solution.

In the example problem involving H2SO4 and NH4OH, how is the molarity of the resulting salt calculated?

In the example problem, the molarity of the resulting salt is calculated by using the number of moles of the limiting reagent (H2SO4 or NH4OH), adjusting for volume changes, and then applying the formula for molarity: M = moles / volume.

How is the pH of a salt solution like NH4Cl determined in an example provided?

For NH4Cl, a salt formed from a weak base (NH4OH) and a strong acid (HCl), the pH is determined using the formula [H+] = √(Kw / Kb × salt concentration × X), where X represents the number of ions from NH4+.