To prepare universal indicator, add 0.18 g of mehtyl red and 0.36 g of phenolphthalein to 550 mL of 95% ethyl alcohol. Next, add 0.43 g of bromthymol blue to 300 mL of DI water. Mix the two solutions and dilute to a final volume of 1 L. Add 0.1 M sodium hydroxide dropwise until the solution is green.
A universal indicator is a pH indicator made of a solution of several compounds that exhibits several smooth colour changes over a wide range of pH values to indicate the acidity or alkalinity of the solution. They are used to indicate the acidity and alkalinity of the solution by colour change.
The Universal Indicator Color Guide shows that Universal Indicator turns red when it is added to a strong acid, it turns purple when it is added to a strong base, and it turns a yellowish-green when it is added to a neutral solution. All acids in the range of 1 to 4 turn the indicator red.
