Imagine that you are in chemistry lab and need to make 1.00 L of a solution with

Question

Imagine that you are in chemistry lab and need to make 1.00 L of a solution with a pH of 2.60. You have in front of you 100 mL of 7.00 times 10^-2 MHCI, 100 mL of 5.00 times 10^-2 MNaOH, and plenty of distilled water. You start to add HCl to a beaker of water when someone asks you a question. When you return to your dilution, you accidentally grab the wrong cylinder and add some NaOH. Once you realize your error, you assess the situation. You have 81.0 mL of HCl and 90.0 mL of NaOH left in their original containers. Assuming the final solution will be diluted to 1.00 L, how much more HCl should you add to achieve the desired pH? Express your answer to three significant figures and include the appropriate units.

Explanation / Answer

pH = 2.6

[H+] = 10^-2.6 = 0.002511 M of H+

mol of H+ = MV = 0.002511*1 = 0.002511mol of H+

V = mol/M = 0.002511/(7*10^-2) = 0.03587 L or 35.87 mL needed

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