pH scale explorer: household substances, indicator colours, pH = −log[H⁺] and dilution

What it does

The pH scale tells you how acidic or basic a solution is, from 0 (very acidic) through 7 (neutral) to 14 (very basic). This page lets you move along the scale and see what changes.

• Drag the pointer along the coloured scale, use the slider, or tap a substance such as lemon juice, milk, soap or drain cleaner. Each substance has a rounded, typical pH.
• The page says whether the solution is acidic, neutral or basic, how much hydrogen ion (H⁺) it holds in mol/L, and how many times more or less H⁺ that is than pure water.
• Indicator colours show what litmus (blue and red), phenolphthalein, methyl orange, turmeric and universal indicator would look like at that pH.
• Add water dilutes the solution 10, 100, 1 000 or more times and shows the new pH.
• The Level switch adds the Class 11 details: [OH⁻], pOH, the ionic product of water Kw and the colour-change range of each indicator.

It follows Class 10 Science (acids, bases and salts: indicators, the pH scale, how strong acid and base solutions are, pH in everyday life) and Class 11 Chemistry (equilibrium: ionisation of water, the pH scale, pH = −log[H⁺]). Next, see how pH changes during a titration in the titration curve simulator, or turn grams into molarity with the concentration converter.

How to use it

1. Tap a substance, or drag along the scale.
2. Read the result and the formula line, which shows the sum with your numbers.
3. Look at the indicator colours. Try the same substance with different indicators.
4. Choose a dilution in Add water and see where the pH ends up.
5. Answer the Check yourself questions; New questions gives a fresh set.

Worked example: lemon juice

Tap Lemon juice (typical pH 2.2). The page reads “pH 2.2: strongly acidic”.

• [H⁺] = 10⁻²·² = 0.00631 mol/L, so pH = −log(0.00631) = 2.2.
• That is about 63 000 (6.31 × 10⁴) times more H⁺ than pure water, which has 10⁻⁷ mol/L.
• Blue litmus turns red, methyl orange is red, phenolphthalein stays colourless, turmeric stays yellow and universal indicator is red.

Now dilute it 100 times. The H⁺ concentration falls 100 times, so the pH goes up by log 100 = 2, to 4.2. Dilute it 10 million times and the pH ends near 7 but stays just below it: once the acid is very dilute, the H⁺ that water makes on its own matters more than the acid’s.

Why each step is ten times

pH is a logarithm. Going from pH 3 to pH 2 means ten times more H⁺; from 3 to 1 means a hundred times more. That is why a small change in pH, such as in your mouth after sugary food (tooth enamel starts to dissolve below about 5.5) or in soil for crops, can make a big difference.

Tips

• Phenolphthalein is the indicator to use when you want to see a base: it is colourless in acids and neutral solutions.
• Turmeric (haldi) stains turn reddish-brown with soap because soap solution is basic.
• At 25 °C, pH + pOH = 14. At other temperatures water’s Kw changes and neutral is not exactly 7.

FAQ

Are the substance values exact? No. They are rounded, typical values. Real lemons, soft drinks and soaps vary.

Why does dilution never make an acid basic? Adding water adds equal amounts of H⁺ and OH⁻, so it can only bring the pH towards 7.

Is anything saved? No. Everything runs in your browser and nothing is stored or sent.

Is this an official textbook tool? No. It is an independent practice page that follows the same school topics.

Last updated 2026-11-09.