Dilution v.s Neutralization Problem

[Lori]

Homework Statement

So, i have two different problems, and I'm not sure why the technique for solving them is different! They look the same! My main problem is whether i should us M1V1 = M2V2 to solve for volume or to use stoic by using a balanced chemical equation...

the first problem is : What volume of 2.50 M HNO3 is needed to completely neutralize 34.6 ml of 1.22 M Ba(OH)2. [/B]
In this case, i used the stoic method to solve for the volume which got my the correct answer of : 33.9 ml. What i did was just convert Ba(OH)2 to the mols and use mole ratio to find vols of HNO3 and converted it to liters... However, using M1V1 = M1V2 does not work in this case.

the second problem is : 10.0g of Ca(OH)2 was added to enough water to make 435 ml Of solution. what volume of this solution should be added to 45 ml of 0.867 M sulfuric acid solution to completely neutralize the acid.?

In this problem, i used the M1V1 = M2V2 which yielded the correct answer! It was fast and simple since all i needed to do was plug into the formula. I didn't need a chemically balanced equation

Homework Equations

M1V1 = M2V2
M = mols/1 liter

 

[mjc123]

Can you think of an obvious chemical difference between HNO₃ and H₂SO₄? (Hint: was your answer out by a factor of 2? If not, I am on the wrong track.)

 

[Lori]

Can you think of an obvious chemical difference between HNO₃ and H₂SO₄? (Hint: was your answer out by a factor of 2? If not, I am on the wrong track.)

There aee 2 mols of H in the second acid right.
Is it because in the first problem, the mols of acid is not equal mols of base OH? So I'd have to use the stoic method?

 

[Borek]

My main problem is whether i should us M1V1 = M2V2 to solve for volume or to use stoic by using a balanced chemical equation...

Stoichiometry works always.

The formula you listed works only for reagents reacting 1:1. I hate it when people teach it as an approach to the titration problems, it is confusing and misguiding, you have just failed into this trap. Forget you ever saw the M1V1 = M2V2 formula, use stoichiometry and you won't ever have problems with any titration question.

 

[Lori]

Stoichiometry works always.

The formula you listed works only for reagents reacting 1:1. I hate it when people teach it as an approach to the titration problems, it is confusing and misguiding, you have just failed into this trap. Forget you ever saw the M1V1 = M2V2 formula, use stoichiometry and you won't ever have problems with any titration question.

I'm kinda aware of this but like I find it easier. So when can I use this formula? For dilutions right? Where m1v1 is initial and m1v2 is final

 

[Borek]

I'm kinda aware of this but like I find it easier. So when can I use this formula? For dilutions right? Where m1v1 is initial and m1v2 is final

Despite looking the same it is not the same formula. For dilutions you have concentration of the same substance on both sides of the equation.

 

[Lori]

Despite looking the same it is not the same formula. For dilutions you have concentration of the same substance on both sides of the equation.

Oh true. Totally forgot about it . That makes sense. Thanks!