[saurabhorange]

I am 15, From India preparing For Worlds Toughest Exam IITJEE I am finding chemistry a little tough I have joined specialized coaching for IITJEE exam and they have provided me with their modules for each subject and in chemistry i am not able to udnerstand law of gram equivalents completely



even if i learn it by heart and apply in practical problems (Acid Base titration problems) There is always a curiosity in my mind what is the proof it How does it work for all reactions I would be really thankful if someone can help me in this I know these things are not taught in USA,UK (atleast to students who are 11th grade 15 years old )

Here is the law

The equivalents of the reactants are equal to each other and also to the equivalents of the products

here is the statement


N1V1=N2V2






Exactly what the title says I am really fed up with the following law as it is used so commonly and in my coaching books and they dont even give its proof

LOOKING FORWARD FOR THE PROOF THANKS 

[Hunter2]

This means matter will not dissapear.

For example hydrogen will be burnt and forms water.

2 H₂ + O₂ => 2 H₂O

On the left side you have 2 hydrogen molecules (together 4 hydrogen atoms) and also 1 Oxygen molecule (2 oxygen atoms).  In sum you have 6 atoms. After reaction you  get 2 water molecules (containing 2 hydrogen and one oxygen atom), in sum these are also 6 atoms. Left and right side you have the same amount.

The mass would be if we talk in moles

2 x 2g + 32 g => 2 * 18 g

36 g => 36 g

[Borek]

There is no proof in a strict, mathematical sense. This is a thing that was observed and made into law.

[saurabhorange]

Exactly what i thought thanks from the bottom of my heart I have another question that is also very rare how do we do questions such as

Q. What will be the minimum weight of compound having 8% sulphur by mass

How do you do such kinds of problems the above one involved only one element but what if there were many

[Hunter2]

First thing is you develop the chemical equation. Then you calculate the moles by using given mass or percentages and molar mass and compare.

[saurabhorange]

You didnt got me IF the formula for compound is not given it dosnt reacts with anything its not related to writing equations I

In my chemistry module it is done like this

We need to find out minimum molecular weight of sulphur so we can assume the compound wil have atleast one sulphur atom

and perecentage of sulphur in compound is 8% or whatever %

so

32/molecular weight of comound * 100 =8

we can solve for Molecular weight from here

I dont get this

[Borek]

Compound that contains sulfur must contain at least one atom. If so, 8% of its molecular weight must be at least 32 a.m.u. It gives a simple proportion:

[tex]\frac{8\%}{32\ a.m.u.}=\frac{100\%}{molecular\ weight}[/tex]

[Hunter2]

Simple mathematics.

Molecular weight is 32 g/mol for S and the molecule contain 1 sulfur which is 8% of the compound.

You can say 8% = 32 g/mol  
and 100% = x g/mol

x = 32 g/mol *100% /8% = 400 g/mol

Borek was faster