In a titration of 0.368 L of 1.222 M B solution, how many liters of 1.088 M A solution are required to reach the end-point. A + 2B → 2C + D

Answer 1

Looking at the balanced equation...

A + 2B ==> 2C + D, we see that it takes 1 mole of A to neutralize (react with) 2 moles of B. So, if we know the moles of B present (which we can find from volume and molarity), we can then find mole of A needed. Once we have moles of A needed, we can determine the volume (see below).

moles of B present = 0.368 L x 1.222 moles/L = 0.4497 moles

moles of A needed = 0.4497 moles B x 1 mole A / 2 moles B = 0.2248 moles of A needed

Since A is 1.088 M, we know it has 1.088 moles A/liter. Thus,...

(x L)(1.088 mol/L) = 0.2248 moles

x = 0.2067 liters of A are required

Answer 2

Hello, Annibelle,

[Please note I have made a couple of changes to my original post as per the mistakes J.R. S. pointed out in his comment]

The definition of Molar is moles per liter (moles/liter). The question want to know how many molecules of a 1.088 Molar solution of A will it take to neutralize/react with the number of molecules of B contained in 0.368 L of 1.222 M of B. I used the term molecules, because this is actually what we are calculating when we use the term "moles."

We can determine the number of B molecules by multiplying the volume of B by the concentration of B: (0.368L)*(1.222 mole/L). I used the definition of M in the calculation so that you can see how the units cancel. Liters cancels out and moles moves to the top, so we know we've done the correct operation to get moles.

I get 0.450 moles of B. [Thanks to J.R. S. for pointing out I had the wrong calculation in my first post] This means we have (0.450 moles)*(6.023x10²³molecules/mole) molecules of B. We don't need this long number since we can use moles instead, as a shorthand measure.

To find how many liters of A are required, let's first look at the balanced equation to see how many molecules of B it takes to react with all of the A molecules. The equation says we need 2 B for each A. So if we have 1 mole of A, we'd need 2 moles of B. We found 0.450 moles of B, so we'll need 0.250 moles of A.

Next, find the volume of 1.088M that would contain 0.250 moles of A. Use the definition of Molar:

1.088M = 0.250 moles A/Volume A (in L). I get 0.230 L (or 230 ml).

I hope this helps,

Bob