Eriochrome Black T Solution Preparation

Chemists use an analytical technique called "complexometric titration" to analyze the amounts of dissolved metals in solutions. The technique typically involves placing the metal-containing solution in a beaker or flask and adding a complexing agent, such as ethylenediaminetetraacetic acid, or EDTA, dropwise from a buret. The complexing agent binds to the metals and, after all the metals have been complexed, the next drop of complexing agents binds to an indicator to induce a color change. The color change allows the chemist to know when the titration is complete. Eriochrome black T, or EBT, represents one of the color-changing compounds for such titrations. EBT, however, is a solid and must be prepared as a solution prior to its use as an indicator.

Step 1

Put on gloves and protective eyewear and weigh out approximately 0.5 g of solid Eriochrome Black T, (EBT) on a balance and transfer it to a small beaker or flask. Add about 50 mL of 95 percent ethyl alcohol and swirl the mixture until the EBT has fully dissolved.

Step 2

Weigh out 4.5 g of hydroxylamine hydrochloride on a balance and transfer it to the beaker or flask containing the EBT. Swirl until the hydroxylamine hydrochloride has fully dissolved.

Step 3

Transfer the solution containing the EBT and hydroxylamine hydrochloride to a 100-mL graduated cylinder. Add enough 95 percent ethyl alcohol to bring the total volume to exactly 100 mL.

Step 4

Transfer the EBT solution from the 100-mL graduated cylinder to a dropper bottle and label the bottle "0.5% Eriochrome Black T in Ethanol."