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.

Application

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.