A ruler for acids

The idea

The pH scale measures hydrogen ion concentration in a solution, generally from 0 (very acidic) to 14 (very alkaline); pH is a number indicating the acidic or basic nature of a solution.

Where does water sit?

A scientist wants one number to say how acidic or basic a liquid is. The number runs from 0 at one end to 14 at the other.

Where would pure water sit on this ruler?

• In the middle, at 7
• At 0
• At 14

Slide along the scale

Tap a liquid to send the marker to its pH. Or slide the marker yourself.

pH is a number

The pH scale measures the hydrogen ion concentration in a solution, generally from 0 (very acidic) to 14 (very alkaline). pH is a number that shows whether a solution is acidic or basic.

The p in pH stands for *potenz*, German for power. The pH values here are typical; real juices vary a little.

• pH | The solution is
• 0 | very acidic
• less than 7 | acidic
• 7 | neutral
• more than 7 | basic (alkaline)
• 14 | very alkaline

Notes

The pH scale measures hydrogen ion concentration in a solution, generally from 0 (very acidic) to 14 (very alkaline); pH is a number indicating the acidic or basic nature of a solution.

Check yourself

What does a pH number tell us?

Which pH is very acidic?

Pure water has pH …

Milk of magnesia has a pH of about 10.5. It is …

• Whether a solution is acidic or basic — correct. Yes!
• How hot the solution is. Heat is measured with a thermometer, not pH.
• How much the solution weighs. pH is about acidic or basic nature.
• 0 — correct. Yes! The scale starts at 0 for the very acidic end.
• 7. 7 is neutral, the middle.
• 14. 14 is the very alkaline end.
• 0. 0 is very acidic.
• 7 — correct. Yes! Neutral.
• 14. 14 is very alkaline.
• basic (alkaline) — correct. Yes! More than 7 means basic.
• acidic. Acids have pH less than 7.
• neutral. Neutral is exactly 7.