GRE Subject Test: Chemistry : Indicators and Complexometry
Study concepts, example questions & explanations for GRE Subject Test: Chemistry
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Example Questions
Example Question #11 : Acid Base Chemistry
250mL of 2N 
Basic and yellow
Acidic and green
Basic and green
Acidic and yellow
Neutral and green
Acidic and green
Each of these compounds requires one equivalent of H+ is added to 100mL of 5N NH3 mol, so for HClO4, 2N = 2M, and for NH3, 5N = 5M.
Using the concentrations and volumes, we can find the moles, finding 
In this case, equivalents of acid are equal to the equivalents of base, meaning that we are at the equivalence point in a titration. HClO4 is a strong acid, and NH3 is a weak base.
Thus, the acid will fully dissociate, while the base will not, resulting in a greater concentration of H+ than OH– in the solution. This means the resulting solution will be acidic. We know that the indicator changes from yellow to green at 8.3, which is a basic pH. Our initial solution is basic, and we must pass through the pH of 8.3 to reach our final acidic solution, with pH < 8.3, meaning that the indicator must change from yellow to green during the reaction. This gives out final answer that the solution will be acidic and green.
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