[EddyJuaniMeron]

I have many questions that I don't understand from my chemistry practice. The practice has a total of 100 problems but these are the ones that we didn't understand at all. We appreciate if you could at least do some of them. And sorry if some terms are incorrect since we are translating from spanish to english

1) How many ml of H2SO4 (density =1,84 and 93% pure) are needed to prepare 700ml of a solution 1,3M. Also determine the molality and normality.

2) How many grams of ethanol are  in 400g of solution of ethanol 0,25 molal?

3) Measure the volume necessary to prepare 100ml of a solution 0,45N of Aluminium hydroxide (density = 0,9 and 58% pure).

4) The Magnesium of KMnO₄ is reduced according to the following reaction.

MnO₄^1- + H¹⁺ -------------------- Mn²⁺
What is the normality of 15,75 g of such salt dissolved in 500 ml of solution.

5) 200 ml of sulfuric acid 2M and 300ml of Nitric Acid 0,5N are mixed. Then at the middle of the mixture, 400 ml of NaOH are added and then 200ml of water. Is the solution acid or basic? What is the final normality of the solution?

6) 800 ml of a solution 4M of Calcium Hydroxide reacts with 400ml of a solution 3,5N of Phosphoric Acid. How many grams of the salt are formed? Which is the rreactive in excess and by how many?

If there's any problem understanding the translation please ask.

[Borek]

You have to show your attempts at solving the question to receive help. This is a forum policy.

At least list relevant equations and formulae and see if you can apply them.

[EddyJuaniMeron]

Ok, I'm really sorry for that. Here's my attempt at solving #1.

1) How many ml of H2SO4 (density =1,84 and 93% pure) are needed to prepare 700ml of a solution 1,3M. Also determine the molality and normality.

g = M x MM x V
g = 1,3M x 0,7L x 98g (Molar mass of H2SO4)
g = 89,18g of solute

Pure density = 1,84g/ml x 0,93 = 1,7 g/ml

1,7g/ml = 89,18g/ml
ml = 89,18g/ml/1,7g
ml=52,46ml

I think that this would be the answer for question A but the thing is that I'm not really sure if the gram I get from the first formula can be used to get the ml.

Normality = moles of solute/kg of solvent

I still can't understand this concept. I would show my attempts but the thing is that I don't even know how to start here.

I don't really get how are we supposed to get the kg of solvent or the moles of solute. Since we only have the g of solute I think.

Normality = g/Meq(V)

[Arkcon]

Normality = moles of solute/kg of solvent

Normality = g/Meq(V)

These two formulas aren't correct.  So, that's another source of the problems you're having.  Normaility is defined here:  http://en.wikipedia.org/wiki/Normality_%28chemistry%29  And I'm sorry there isn't an entry in the Spanish language wikipedia.

[Borek]

1,84g/ml x 0,93 = 1,7 g/ml

Your approach to the first problem is correct, but what you did here is not. You should not round intermediate results. That is - you should report them rounded, but when using them for further calculations you should use at least several additional guard digits. Better yet, do calculations in such a way you don't need to reenter them into your calculator. In this case 1.84*0.93=1.7112 - too many significant digits, but you should use them in this step instead of 1.7:

ml = 89,18g/ml/1,7g
ml=52,46ml

and you would get 52.1 mL.