Acidic and basic aqueous solutions can be identified using dyes called indicator

Question

Acidic and basic aqueous solutions can be identified using dyes called indicators. A common indicator in chemistry shows acidic solutions (excess of H^+ ions) as red and basic solutions (excess of OH^- ions) as blue. Consider the following neutralization reaction: H_2S0_3(aq) + 2KOU(aq) K^2SO^3(aq) + 2H20(/) Suppose an acidic aqueous solution containing 0.0170 mol of sulfurous acid (H2SO3) is added to another basic aqueous solution containing 0.0289 mol of potassium hydroxide (KOH). Answer the following questions: How many moles of potassium hydroxide are neutralized by the sulfurous acid? Which reactant is in excess? After mixing, if you dipped one of the indicator strips into the solution, would the strip be red (acidic) or blue (basic)?

Explanation / Answer

ratio is 1:2

that is, 1 mol foH2SO3 per 2 mol of KOH

if 0.017 mol of H2SO3 then 0.017*2 = 0.034 mol of KOH are needed

the reagent in excess

H2SO3 since there is plenty of H2SO3; and KOH will not be enough to react

since there is excess of H2SO3

expect H+ in solution, that is a low pH, or a red litmus!

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