pH Scale Lab

🧪 ONLYGYAANI CHEMISTRY VIRTUAL LAB

pH Scale Virtual Lab

Explore the pH scale from 0 to 14. Test common substances, observe universal-indicator colours and investigate how hydrogen and hydroxide ion concentrations change with pH.

🍋 pH 0–6 Acidic
💧 pH 7 Neutral at 25°C
🧼 pH 8–14 Basic
🌈 Indicator Colour scale
🌈 Interactive pH Scale
CURRENT SOLUTION Pure Water pH 7 NEUTRAL H⁺ 1×10⁻⁷ M Hydrogen ions OH⁻ 1×10⁻⁷ M Hydroxide ions pH SCALE 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 pH 7 ACIDIC NEUTRAL BASIC
🎛 pH Controls
🧪 pH Value pH 7.0
0 Strongly acidic 7 14 Strongly basic
🧴 Common Solutions Pure Water
pH 7.0
Nature Neutral
[H⁺] 1.00 × 10⁻⁷ M
[OH⁻] 1.00 × 10⁻⁷ M
Universal Indicator Green
pOH 7.0
Neutral solution
At pH 7.0, [H⁺] and [OH⁻] are equal in this 25°C model.
pH relationship

pH = −log₁₀[H⁺]
[H⁺] = 10−pH

At 25°C:
pH + pOH = 14
[H⁺][OH⁻] = 1.0 × 10−14

🎯 pH Challenge

Move the slider until the hydrogen-ion concentration is approximately 1 × 10⁻³ M.

Current [H⁺] = 1.00 × 10⁻⁷ M

🎯 Aim

To study the pH scale and investigate the relationship between pH, hydrogen-ion concentration and hydroxide-ion concentration.

🧰 Apparatus

Virtual pH scale, universal indicator, test solutions, beaker and digital concentration display.

📘 What is pH?

pH is a logarithmic measure related to hydrogen-ion activity in an aqueous solution. In introductory calculations, hydrogen-ion concentration is commonly used as an approximation.

Lower pH → more acidic

Higher pH → more basic

🔢 pH is Logarithmic

A change of one pH unit represents a tenfold change in hydrogen-ion concentration in the simplified concentration model.

pH 3:
[H⁺] = 10⁻³ M

pH 4:
[H⁺] = 10⁻⁴ M

Therefore pH 3 has approximately ten times the hydrogen-ion concentration of pH 4.

⚖️ Acidic, Neutral & Basic

Acidic: pH below 7

Neutral: pH 7 at 25°C

Basic: pH above 7
The neutral pH depends on temperature. The pH 7 neutral point used in this lab corresponds to the standard introductory 25°C model.

🌈 Universal Indicator

Universal indicator contains a mixture of indicators that produces a range of colours across different pH values.

pH 0–2 → Red
pH 3–4 → Orange
pH 5–6 → Yellow
pH 7 → Green
pH 8–10 → Blue
pH 11–14 → Violet/Purple

🧪 Experiment

Compare:

Lemon Juice
Vinegar
Pure Water
Baking Soda Solution
Soap Solution
Ammonia

Record pH, [H⁺], [OH⁻], pOH and indicator colour.

📊 Observation Table

Trial Substance pH pOH [H⁺] [OH⁻] Indicator Colour Nature
No observations recorded.

🔍 Expected Observations

As pH decreases, calculated [H⁺] increases.
As pH increases, calculated [OH⁻] increases in the 25°C model.
At pH 7, [H⁺] = [OH⁻] = 1 × 10⁻⁷ M.
Every one-unit pH change corresponds to a factor of ten in [H⁺].

📝 Procedure

  1. Select a common substance or move the pH slider.
  2. Observe the pH-scale pointer.
  3. Observe the universal-indicator colour.
  4. Read [H⁺] and [OH⁻].
  5. Identify whether the solution is acidic, neutral or basic.
  6. Record the observation.
  7. Change pH by one unit.
  8. Compare the change in hydrogen-ion concentration.
  9. Repeat using several substances.

💡 Remember

pH is a logarithmic scale.
A lower pH corresponds to greater hydrogen-ion concentration.
pH + pOH = 14 is used here for aqueous solutions at 25°C.
Household-substance pH values are approximate and can vary with concentration and composition.

🎓 Quick Viva Questions

1. What does pH measure?

pH is defined in terms of hydrogen-ion activity and indicates the acidity or basicity of an aqueous solution.

2. What is the pH of a neutral solution at 25°C?

Approximately 7.

3. What is [H⁺] when pH = 3 in the simplified model?

1 × 10⁻³ mol/L.

4. What happens to [H⁺] when pH increases by one unit?

It decreases by a factor of ten.

5. What is pOH when pH = 4 at 25°C?

pOH = 14 − 4 = 10.

6. What colour does universal indicator generally show near pH 7?

Green.

7. Is pH 2 twice as acidic as pH 4?

No. The pH scale is logarithmic. In terms of hydrogen-ion concentration, pH 2 has about 100 times the [H⁺] of pH 4.

✅ Result

The pH scale provides a logarithmic measure of acidity and basicity. In the simplified concentration model, decreasing pH increases hydrogen-ion concentration by a factor of ten for every pH unit, while increasing pH decreases hydrogen-ion concentration.

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