Unit 15: Molarity, pH Scale, and Strengths of Acids and Alkalis

Flashcards covering molarity, pH scale, and strengths of acids and alkalis.

Molarity of a solution

The number of moles of solute dissolved in 1 dm³ of the solution.

Molarity of a solution (mol dm³)

number of moles of solute (mol) / volume of solution (dm³)

Methyl orange

red in dilute hydrochloric acid, yellow in dilute sodium hydroxide solution

Litmus solution

red in dilute hydrochloric acid, blue in dilute sodium hydroxide solution

Phenolphthalein

colourless in dilute hydrochloric acid, pink in dilute sodium hydroxide solution

pH formula (to find pH)

pH = -log10[H+(aq)]

Calculate concentration of H ions

[H+(aq)] = log^(-pH)

pH scale

A scale used to measure the degree of acidity or alkalinity of a solution, ranging from 0 to 14.

Methods to measure pH values

using universal indicator solution, using a pH meter, and using a pH sensor attached to a data-logger.

Strong acid

An acid that dissociates almost completely in water to give hydrogen ions.

Weak acid

An acid that dissociates partially in water to give hydrogen ions.

Compared to a weak acid, a strong acid has

lower pH, higher electrical conductivity, higher rate of reaction with metals.

Strong alkali

An alkali that dissociates almost completely in water to give hydroxide ions (OH(aq)).

Weak alkali

An alkali that dissociates partially in water to give a small amount of hydroxide ions (OH(aq)).

Compared to a weak alkali, a strong alkali has

higher pH and higher electrical conductivity.

The strength of an acid or alkali

Refers to how much it dissociates in water.

The concentration of an acid or alkali

Refers to the amount of acid or alkali dissolved in a unit volume of solution.