[BreakingB619]

Hello. I'm stuck with a couple of questions as I'm not sure how to approach them and what formula to use. I could use a hint or two.

1.) Calcium hydride combines with water according to the equation: CaH2(s) + 2H2O(l) >> 2H2(g) + Ca(OH)2(s)
Beginning with 84.0g of CaH2(s) and 36.0g of H2O, what volume of H2 will be produced at 273K and a pressure of 2 atm?

I tried using the formula PV=nRT but I'm not sure how to find "n". I add 84g CaH2 and 36g H2O, together and I get 120g. Am I suppose to do stoichiometry at this point? I tried to but I couldn't figure it out how to get the # of H2. It's my first chemistry class so I could use some help.

2.) Calculate the volume of 0.500 M KOH required to neutralize 150ml of 0.100 M HCl.

KOH is a strong base and HCl is obviously an acid. Am I over analyzing this question? 150ml of KOH should be enough to neutralize it right? I'm not sure how else to approach this problem, I tried using (M1)(V1)=(M2)(V2) formula but I don't think that's right. Any hints?

[UG]

1.) Calcium hydride combines with water according to the equation: CaH2(s) + 2H2O(l) >> 2H2(g) + Ca(OH)2(s)
Beginning with 84.0g of CaH2(s) and 36.0g of H2O, what volume of H2 will be produced at 273K and a pressure of 2 atm?

Ok, do you know how to calculate the number of moles of CaH₂ and H₂O using the masses given and their molar masses? Once you have solved this, you need to look at your balanced equation and decide if any of the two substances is 'limiting' the reaction (ie, there may be an excess of one substance which does not react). A bit of stoichiometry should then get you the number of moles of H₂ produced (which is the 'n' in your equation PV=nRT). See how you go with this one.

2.) Calculate the volume of 0.500 M KOH required to neutralize 150ml of 0.100 M HCl.

KOH is a strong base and HCl is obviously an acid. Am I over analyzing this question? 150ml of KOH should be enough to neutralize it right? I'm not sure how else to approach this problem, I tried using (M1)(V1)=(M2)(V2) formula but I don't think that's right. Any hints?

Your approach of M₁V₁ = M₂V₂ is correct.

[BreakingB619]

Ok, do you know how to calculate the number of moles of CaH₂ and H₂O using the masses given and their molar masses? Once you have solved this, you need to look at your balanced equation and decide if any of the two substances is 'limiting' the reaction (ie, there may be an excess of one substance which does not react). A bit of stoichiometry should then get you the number of moles of H₂ produced (which is the 'n' in your equation PV=nRT). See how you go with this one.


Your approach of M₁V₁ = M₂V₂ is correct.

Ok, I solved both in about 2 minutes lol. I got 22.4L for the first question and 750ml for the second question. Is that correct? if I am, then those questions are actually pretty simple and my brain just needed a break from studying (finals). Let me know if I got them right, thanks again for the help.

[UG]

Ok, I solved both in about 2 minutes lol. I got 22.4L for the first question and 750ml for the second question. Is that correct? if I am, then those questions are actually pretty simple and my brain just needed a break from studying (finals). Let me know if I got them right, thanks again for the help.

Yes I got 22.4 L for the first one too. Don't know how you got 750 mL for the second one though, probably got your multiply and division mixed up (if this is the case, you definitely need a break )

[BreakingB619]

oops.. I may have plugged in the wrong values in the wrong places haha. 30 ml 

[UG]

Ah, that looks better.

[Borek]

I tried using (M1)(V1)=(M2)(V2) formula but I don't think that's right.

And you are right about the formula being - in general - wrong. It works, but by accident, as KOH and HCl react 1:1. The same formula will fail miserably for the reaction between KOH and H₂SO₄.

Compare http://www.titrations.info/titration-calculation - while the page is about titration, acid base titrations are just neutralization reactions, so everything works the same way as in your question.