Kaplan Gen. Chem Question

[jdpaul14]

Q: 100 mL of 5M H2SO4 (aq) are diluted to 800 mL. What is the molarity of the solution after dilution?

A: 5/8 M

My question is, why aren't we using Normality here? I would have used N1V1 = N2V2, and then solved for N2

Hopefully someone can help me,

Thanks

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[nze82]

Q: 100 mL of 5M H2SO4 (aq) are diluted to 800 mL. What is the molarity of the solution after dilution?

A: 5/8 M

My question is, why aren't we using Normality here? I would have used N1V1 = N2V2, and then solved for N2

Hopefully someone can help me,

Thanks

Normality is essentially the concentration of the "Reactive Species." So, in general, you will use normality only when some sort of reaction is occurring (Example: When you're adding Acid to Base, you're essentially promoting a neutralization reaction, which is why you can use normality). However, in your example, you're simply adding water to dilute the acid. Adding water doesn't promote any reactions. So, having a "Reactive Species" is meaningless, which is why you use molarity rather than normality.

 

[jdpaul14]

Oh...got it, thanks buddy!

 

[doc toothache]

Q: 100 mL of 5M H2SO4 (aq) are diluted to 800 mL. What is the molarity of the solution after dilution?

A: 5/8 M

My question is, why aren't we using Normality here? I would have used N1V1 = N2V2, and then solved for N2

Hopefully someone can help me,

Thanks

You can use the N1V1=N2V2 but in the case of H2SO4 there are two available hydrogens and, therefore, 1M=2N. Since it is asking for molarity you can pretend that there is no difference. The answer does not change.