O 12/2/2016 11:55 PM A 86.7/100 11/15/2016 04:01 AM Gradebook Print Calculator l

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O 12/2/2016 11:55 PM A 86.7/100 11/15/2016 04:01 AM Gradebook Print Calculator l Periodic Table Question 8 of 27 Incorrect X Incorrect Incorrect Incorrect Map Sapling Learning macmillan learning Reset mL The flask shown here contains 0.467 g of acid and a few drops of phenolphthalein indicator dissolved in water. The buret 20 contains 0.100 M NaOH 10 15 What volume of base is needed to reach the end 20 25 point of the titration? 25 Number 30 30 35 25.00 mL base 40 45 50 What is the molar mass of the acid (assuming it is diprotic and that the end point corresponds to Add base to the solution until the second equivalence point)? it just turns pink. You may need to reset the titration if Number you go past the end point. 372.11 g mol You may not have reached the end point of the titration yet, or you may be reading the volume in the buret incorrectly Once you see pink that fades away in the flask continue adding base drop by drop until the pink color persists in the flask Previous & Give Up & View Solution Try Again Next Exit

Explanation / Answer

Step 1: Number of moles of NaOH consumed to neutralize the acid solution =

Molarity of NaOH solution x Volume of NaOH solution

= 0.10 M x X ml = 0.1 X moles

Note: Molarity = moles / Liter. So, molarity x volume (in L) = (moles/ L) x L = moles]

Note: It seems are you are running online titration (simulation/ programs). So, it is not possible to correctly know the volume of base required for neutralization. For simplicity, it’s assume that, the voume of base required = X liter. Be noted, the volume must be in terms of Liters to get (M x Vol = moles). So, if the volume of base consumed were 25 mL, it is equal t0 0.025 L.

Step 2: Since the acid is diprotic, one mole of its donates 2 H+.

That is 1 mol acid is neutralized by 2 moles base. Or, 1 mole base neutralizes (1/2) moles acid.

So, number of moles of acid neutralized by base = (1/ 2) x number of moles of NaOH

                                                            = (1/2) x (0.1X) = 0.05X moles.

Now,

Molar mass of the acid = mass / number of moles

                                    = 0.467 g / (0.05 X) moles = (9.34 / X) g mol-1

Note: First get the correct value volume (in Liters; use 1 L = 1000 mL) of NaOH required to neutralize acid. No one will be able to run the online simulation of titration in your place, so please do it yourself.

Just divide that volume (in Liter) of NaOH to 9.34, you get the molar mass of the acid.

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