Feynman teaching note

Acids, Bases, and pH

SubjectChemistry

Area tags

Chemistry

pH measures how many free hydrogen ions (H+) are floating in a solution. More H+ means more acidic. The scale runs 0 to 14, with 7 being neutral (pure water). The sneaky part: the scale is logarithmic. Each step is a factor of ten. pH 4 is ten times more acidic than pH 5 and a hundred times more than pH 6. So lemon juice (pH 2) isn't 'a bit more sour' than coffee (pH 5); it has a thousand times more H+. Bases are the opposite: they soak up H+ (or release OH-), pushing pH above 7. Mixing an acid and a base lets their H+ and OH- combine into water, dragging pH back toward neutral. That's neutralisation, and it's why antacids calm an acidic stomach.

Same topic, fresh practice—does not count as an adaptation.

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Clarity score: 82/100How well you know it: Can use it anywhere

Explain why going from pH 3 to pH 6 is a thousand-fold change, not a threefold one.

Doesn't define what a base does as precisely as what an acid does.
Skips why the scale typically stops around 0 and 14.

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