Help with Chemistry

[EunSoo]

Hello! I need some help with a chemistry titration problem:

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a) If 25 mL of 1.00 M HCl is mixed with 75 mL of 1.00 M NaOH, how many moles of each ion are present BEFORE the reaction?

          Na+ = _ moles

          Cl- = _ moles

          H3O+ = _ moles

          OH- = _ moles

 

and

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c) What are the FINAL concentrations of all ions present?

          [Na+] = _ M

          [Cl-] = _ M

          [H3O+] = _ M

          [OH-] = _ M

 

I know how to find molarity or how many ml or moles of HCl and NaOH but I have no idea about the other side of the equation. Can anyone give me a hint or any pointers on how to proceed? Thanks!

[davrosG5]

If you know how to calculate the molarities of the reagents before mixing you've essentially already got the answer. The levels of sodium and chloride will be unchanged as they don't go anywhere.

For questions C, as this is a neutralisation reaction the H+ (or H3O+ as you've written it) reacts with the OH- to give water. As there is an excess of OH- it will react with ALL of the H3O+ present so assuming the reaction goes to completion (which it will in this case) you effectively have zero H3O+ and 2/3 of the OH- that you started with.

 

Another way to look at it is that all of the initial HCl has been consumed by the reaction and turned into NaCl and water. As there was an excess of NaOH to start with the remainder of the NaOH that wasn't needed to react with the HCl is still present. As this is all taking place in solution the amount of Na and Cl present remains the same as it was initially but it is a different form (you have a mixture of NaCl and NaOH (and some extra water) rather than HCl and NaOH). The H and OH have reacted to form water.

 

Hope that helps