equivalent weight

[san001]

What is the equivalent weight of acid if 1.321gm acid reacts with magnesium to give 1.72gm salt?

[John Cuthber]

Is this homework help?

[studiot]

san, you have mentioned equivalent weight which is an old fashioned term not often taught nowadays.

When you reply to John's question about homework please tell us the circumstances of this question so we can find out if you really need the equivalent weight or another property.

[John Cuthber]

The equivalent weight is one of the few things you can calculate from the information given, so I think it probably is what they want to know.

However, it looks like a homework question.so I think it should be here

http://www.scienceforums.net/forum/35-homework-help/

and follow the rules for that section.

[san001]

I am sorry that I posted in wrong place. I am new and this is my first question. I am preparing for entrance exam and I am unable to solve this type of objective question. How to solve this question? I have posted full question here no any circumstances are given in the question.

should i post same question in homework section?

[studiot]

Don't worry about posting it in the wrong place, the mods will easily fix that.

 

What I was trying to find out is if you know what equivalent weight means, given that it is a (nearly) obsolete term.

 

Or if you like do I need to explain that part to help you solve the question?

 

The actual calculation is trivial, do you know the normal valency of magnesium?

You will also need to look up the atomic weight of magnesium, if you haven't already done so.

 

Here is a sample equation of the type in the question, the reaction of permanganic acid with magnesium to form a salt plus something else.

 

Mg + 2HMnO₄ = Mg(MnO₄)₂ + H₂

Edited June 7, 2015 by studiot

[John Cuthber]

In order to tell you how to solve the problem we need to know how well you understand it.

The easiest way for us to do that is for you to show us how far you have got so far with answering it.

 

The significance of the homework help area is that, when you post stuff there, it makes it clear that you will get help; but not the answer.

"Homework Help Rules A simple reminder to all: this is the "Homework Help" forum, not the "Homework Answers" forum. We will not do your work for you, only point you in the right direction. Posts that do give the answers may be removed."

[san001]

i know about the term equivalent weight. Equivalent weight of magnessium is 12 and valency is 2. I have solved similar question in which known salt was given or equivalent weight of salt is given. I used "number of gram equivalent weight of acid = no. of gram eq. wt. of salt/or any other compound". Generaly number of gram equivalent weights are equal in a balanced equation. But in this question neither known salt nor eq. wt. of salt is given. Instead of this magnesium is added in the question. And i dont know how to use magnesium (or eq. wt. of magnesium) to find solution. Please give some hints.

[John Cuthber]

It often helps to start by writing an equation. Can you do that here?

(Since you don't know anything about the acid you will have to make up a dummy formula for it. The "traditional" one is H_xA where x is the number of protons that acid can give up.

[san001]

I took acid as HxA where A is anion. And the equation became

 

HxA + Mg -> MgxA2 + H2.

 

Then we know eq. wt. of H, Mg also we know the wt. of salt and acid.

I used concept that no. of gram eq. weights are equal. Also eq wt of acid = eq wt of H(1.008) + eq wt of anion (this is unknown say 'e') and eq wt of salt = eq wt of Mg(12) + ew wt of anion. And by solving

 

wt of acid/eq wt of acid = wt of salt/eq wt of salt.

 

I got e=35.38. Thus eq wt of acid=e+1.008=36.39.

Is this correct or not? But the ans given is 36.5.

Edited June 8, 2015 by san001

[John Cuthber]

I would need to check the arithmetic to be certain, but I think you have got it sorted out .

Well done.

The small difference between your answer and that given is probably because the equivalent weight of magnesium isn't exactly 12; it's 12.153