Acids and Alkalis - The pH Scale

Acids are substances that have a pH value less than $7$. They often have a sour taste and turn blue litmus paper red.

Alkalis are bases that are soluble in water. They have a pH value greater than $7$, feel soapy to the touch, and turn red litmus paper blue.

The pH scale is a numerical range from $0$ to $14$ used to measure how acidic or alkaline a solution is. A pH of $7$ is considered neutral ($pure \ H_2O$).

Indicators are substances that change color depending on the pH. Universal Indicator provides a spectrum of colors: red/orange for acids, green for neutral, and blue/purple for alkalis.

Neutralization is a chemical reaction where an acid reacts with an alkali to produce a neutral solution of salt and water. The $H^+$ ions from the acid react with $OH^-$ ions from the alkali.

Common laboratory acids include Hydrochloric acid ($HCl$) and Sulfuric acid ($H_2SO_4$). A common alkali is Sodium hydroxide ($NaOH$).