HCl(aq) → H+(aq) + Cl-(aq)
Acidic solutions have pH values less than 7.
NaOH(aq) → Na+(aq) + OH-(aq)
Alkaline solutions have pH values greater than 7.
A neutral solution is neither acidic nor alkaline. A neutral solution has a pH value of 7.
Acid-alkali indicators can show whether a solution is acidic, neutral (pH 7) or alkaline. The table shows the colours for two different common indicator solutions.
Describe the limitations of methyl orange when determining if a solution is alkaline.
Methyl orange is yellow in neutral solutions as well as in alkaline solutions, so you can only be sure that a solution is acidic if methyl orange turns it red.
Describe the limitations of phenolphthalein when determining if a solution is acidic.
Phenolphthalein is colourless in neutral solutions and in acidic solutions, so so you can only be sure that a solution is alkaline if phenolphthalein turns it pink.
The pH scale measures the acidity or alkalinity of a solution. The pH of a solution can be measured using a pH probe, or estimated using universal indicator and a colour chart.