Lab 4 overview - acids, bases, and buffers

The Ballroom Buffer Dancers

Two partners. One trophy. That trophy is the proton (H⁺). They pass it back and forth so the dance floor never floods and never goes empty.

The cast

Acid Antonio

HA - holds the trophy

Base Bella

A⁻ - empty-handed

The Intruder

H⁺ from HCl

The Thief

OH⁻ from NaOH

Why they are "weak" (in a good way)

Strong acids dump every trophy on the floor and walk away. Antonio keeps almost all of his. That leftover stock is the buffer. Same concentration, very different pH:

0.1 M acid	What happens	Typical pH
HCl (strong)	Every molecule breaks: HCl → H⁺ + Cl⁻	~1
CH₃COOH (weak)	Almost all stay intact: CH₃COOH ⇌ CH₃COO⁻ + H⁺	~2.9

Same 0.1 M. The gap is strength, not concentration. Diluting HCl does not make it weak.

Two directions. One pair.

1. Adding acid - Bella catches the trophy

Key concept: the conjugate base does the work

A pushy guest (H⁺ from HCl) storms in waving extra trophies.
Bella takes the trophy and becomes Antonio.
The dance continues. Free H⁺ barely rises, so pH barely falls.
Net: A⁻ + H⁺ → HA

2. Adding base - Antonio hands the trophy over

Key concept: the weak acid does the work

A thief (OH⁻ from NaOH) tries to steal trophies.
Antonio hands his over. The thief leaves as water (H₂O).
The dance continues. Free OH⁻ is gone, so pH barely rises.
Net: HA + OH⁻ → A⁻ + H₂O

Who catches what - two buffers, same job

Buffer	Catches added acid	Catches added base
Acetate CH₃COOH + CH₃COO⁻	CH₃COO⁻ (Bella) CH₃COO⁻ + H⁺ → CH₃COOH	CH₃COOH (Antonio) CH₃COOH + OH⁻ → CH₃COO⁻ + H₂O
Ammonia NH₃ + NH₄⁺	NH₃ (Bella) NH₃ + H⁺ → NH₄⁺	NH₄⁺ (Antonio) NH₄⁺ + OH⁻ → NH₃ + H₂O

Same two columns either way. The hats are just counted from the other end on the ammonia pair.

Your six beakers

Beaker	In it	You add	Who works	ΔpH
1	Distilled water	5 drops 0.1 M HCl	Nobody. H⁺ stays free.	large ↓
2	Distilled water	5 drops 0.1 M NaOH	Nobody. OH⁻ stays free.	large ↑
3	Acetate buffer	5 drops 0.1 M HCl	Bella: CH₃COO⁻	small ↓
4	Acetate buffer	5 drops 0.1 M NaOH	Antonio: CH₃COOH	small ↑
5	Ammonia buffer	5 drops 0.1 M HCl	Bella: NH₃	small ↓
6	Ammonia buffer	5 drops 0.1 M NaOH	Antonio: NH₄⁺	small ↑

Beakers 1 and 2 are the control. Every "small" number only means something compared with those two. Acetate defends ~4.7. Ammonia defends ~9.3. Both resist. There is no pH-7 rule.

Memory Hook

A buffer is a dance pair, one trophy apart. Acid arrives - Bella takes it. Base arrives - Antonio gives it. The floor never floods and never goes empty, until the partners run out.

🧬 Tehrani Labs 2026 - Interactive Learning Guide
"Same 0.1 M. HCl reads ~1. Acetic acid reads ~2.9. That gap is why a buffer can exist."

Cast: Antonio = weak acid (HA) · Bella = conjugate base (A⁻) · trophy = the proton. Companion to the Lab 4 acids, bases and buffers bench guide. Self-contained page: inline styles only, no scripts, no external assets.