Based on the balanced equation, what volume of .250 M of S2O3(aq) is needed to c

Question

Based on the balanced equation, what volume of .250 M of S2O3(aq) is needed to completely react with 12.44 mL of .125 M of I3(aq)? 2S2O3^2- (aq) + I3- (aq) --> S4O6^2- (aq) + 3I-(aq)

Explanation / Answer

1.) Step 1: Find how many moles of NaOH you added to the drink. moles = volume * molarity moles = .03351 L * 0.0102 moles/L moles = 0.000341802 moles NaOH Step 2: Since you need 3 moles NaOH per mole of C6H8O7, you must have 0.000113934 moles of C6H8O7. Step 3: Find the mass of C6H8O7. 192.13 g/mol * 0.000113934 mole = 0.0219 g C6H8O7 (solution!) 2.) In the photographic process, silver bromide is dissolved by adding sodium thiosulfate. AgBr(s) + 2Na2S2O3(aq) --> Na3Ag(S2O3)2(aq) + NaBr(aq) If you want to dissolve 0.250 g of AgBr (molar mass = 187.8 g/mol), how many milliliters of 0.0138 M Na2S2O3 should you add? Step 1: Find how many moles of AgBr you have: Moles = mass / molar mass moles = .250 g / 187.8 g/mol moles = 0.0013312 moles Step 2: Find how many moles of Na2S2O3 you need: 0.0013312 moles AgBr * 2 = 0.0026624 moles Na2S2O3 Step 3: Find how many mL you need of 0.0138 M Na2S2O3. molarity = moles / volume volume = moles / molarity volume = 0.0026624 moles / 0.0138 M v = 0.192928 L v = 192.93 mL (solution!)

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