3.1.4—pH scale

$pH = −log10[H+]; [H+] = 10^(−pH)$

pH is logarithmic: a one-unit change represents a tenfold concentration change. Universal indicator gives a colour range; a pH probe gives an instrumental pH measurement.

For [H⁺] = 2.0 × 10⁻³ mol dm⁻³, pH = 2.70; the leading 2 makes the answer non-integer. A colour indicator estimates a range, whereas a calibrated probe supports a numerical measurement.

Representative question

[Maximum number: 1]

A solution has a pH of 3.0 . What is the hydrogen ion concentration in the solution in $\mathrm{mol} \mathrm{dm}^{-3}$ ?

$3.0 \times 10^{-3}$

$1.0 \times 10^{-3}$

$1.0 \times 10^{3}$

$3.0 \times 10^{3}$

Retrieve the route: track proton transfer and conjugates, calculate pH and Kw, distinguish strength, balance neutralization, read titration curves, use Ka/Kb and hydrolysis, select indicators, and explain and calculate buffer behaviour.

Check donor versus acceptor, one-proton differences, logarithm direction, ion comparison, strength versus concentration, equivalence versus endpoint, pKa landmarks, conjugate equations and dilution ratios.

3.1.4—pH scale

pH and Hydrogen-Ion Concentration

Calculating pH and [H+]

Assessment in practice

Proton Transfer Reactions Summary

Question 1