Video summary

Titik Didih Larutan Elektrolit | Kimia SMA | Tetty Afianti

Main summary

Key takeaways

Educational

Main ideas / concepts

  • Boiling point elevation in electrolyte solutions (Class 12 / SMA Chemistry) The video explains how to calculate the increase in boiling point when an electrolyte dissolves in a solvent (water), and then how to compute the actual boiling point of the solution.

  • Electrolyte solutions An electrolyte is defined as a solution that breaks down into ions:

    • Positive ions (cations)
    • Negative ions (anions) Examples mentioned: KBr, H₂SO₃, Na₃PO₄, Al₂(SO₄)₃.

  • Counting ions (determining number of ions, n) A compound “contains” its ions based on its formula. Examples:

    • KBr → 2 ions (K⁺ and Br⁻), so it’s treated as a binary electrolyte.
    • H₂SO₃ → 3 ions (2 H⁺ + SO₃²⁻ interpreted as a total of 3 ions; the narration uses “two plus one totals three ions”).
    • Na₃PO₄ → 4 ions (PO₄ counted as one unit, leading to a total of 3 + 1 = 4).
    • Al₂(SO₄)₃ → 5 ions (2 + 3 = 5).

  • Boiling point elevation formula (ΔTᵦ) The method uses:

    • ΔTᵦ = Kᵦ × (mass-based expression) including ionization effects. The subtitles show it (as spoken):

    • ΔTᵦ = Kᵦ × (g / Mᵣ) × 1000/P × (1 + (n − 1)α)

Where:

- **ΔTᵦ** = increase in boiling point (**°C**)
- **Kᵦ** = boiling point elevation constant (**°C·kg/mol**, as typically used)
- **g** = mass of solute (**grams**)
- **Mᵣ** = relative molecular mass
- **P** = mass of solvent (**grams**)
- **n** = number of ions produced per formula unit
- **α (alpha)** = degree of ionization (often given as a percentage)
  • Actual boiling point of solution
    • Tᵦ(solution) = 100°C + ΔTᵦ (Using water’s boiling point as the base in the examples.)

Step-by-step methodology used in the examples

(Formulas and procedure are repeated across multiple example questions.)

  1. Identify the solute Example: NaOH, K₂SO₄, Na₂CO₃, MgCl₂, Al₂(SO₄)₃.

  2. Determine the number of ions, n Use the compound’s formula to count ions produced:

    • Binary electrolytes: n = 2 (e.g., NaOH, KBr in the narration)
    • Ternary/quaternary and higher: n = 3, 4, 5 depending on formula (as stated in subtitles)

  3. Determine Mᵣ (relative molecular mass) Compute from atomic masses given in the problem (as repeatedly done in the subtitles).

  4. Compute ΔTᵦ Use:

    • ΔTᵦ = Kᵦ × (g / Mᵣ) × 1000/P × (1 + (n − 1)α)

  5. If the problem asks for the degree of ionization α

    • Use: Tᵦ(solution) = 100 + ΔTᵦ
    • Compute ΔTᵦ from the given boiling point.
    • Rearrange the formula to solve for α (demonstrated in the last example).

  6. Compute final boiling point if needed

    • Tᵦ(solution) = 100 + ΔTᵦ

Example questions covered (what each one solves)

Example 1: NaOH

  • Given: 1.6 g NaOH in 500 g water
  • Known: Kᵦ = 0.52
  • Degree of ionization α assumed as 1 (if α isn’t given, take it as 1)
  • Ion count: NaOH treated as n = 2
  • Result:
    • ΔTᵦ ≈ 0.08°C
    • Tᵦ ≈ 100.08°C (shown in subtitles as 100.0 8°C)

Example 2: K₂SO₄

  • Given: 1.74 g K₂SO₄ in 200 g water
  • Known: Kᵦ = 0.502, α = 20% → 0.2
  • Ion count:
    • K₂SO₄ treated as n = 3
  • Result:
    • ΔTᵦ ≈ 0.036°C
    • Tᵦ ≈ 100.36°C

Example 3: Find mass of Na₂CO₃

  • Given: Mᵣ Na₂CO₃ = 106, 500 g water
  • Given boiling point: 100.04°C
  • Known: Kᵦ = 0.52, α = 0.23
  • Ion count: Na₂CO₃ → n = 3
  • Method: compute ΔTᵦ from boiling point, then solve for g
  • Result:
    • g ≈ 3.85 g Na₂CO₃

Example 4: Find mass of MgCl₂

  • Given: MgCl₂ dissolved in 300 g water
  • Boiling point: 100.6°C
  • Known: Kᵦ = 0.502, α = 0.5
  • Ion count: MgCl₂ → n = 3
  • Result:
    • g ≈ 16.4 g MgCl₂

Example 5: Find degree of ionization α for Al₂(SO₄)₃

  • Given: Al₂(SO₄)₃ = 34.2 g, 1 liter water (1000 g)
  • Boiling point: 100.094°C
  • Known: Kᵦ = 0.5
  • Ion count: Al₂(SO₄)₃ → n = 5 (2 from Al part and 3 from SO₄ part)
  • Compute:
    • ΔTᵦ = 100.094 − 100 = 0.094°C
    • Substitute into the ΔTᵦ formula and rearrange to solve for α
  • Result:
    • α ≈ 20%

Speakers / sources featured

  • Tetty Afianti (presenter/teacher, as indicated by the video title)
  • No other clearly identifiable named speakers or sources are mentioned in the provided subtitles (though the subtitles refer to visiting a “chemistry blog”/blogspot for more practice without a specific author).

Original video