[sahilmangal]

Hey there.. Although I'm in Xth Grade.. My Basics about chemistry are nnot clear.. like valencies.. chemical combining.. reactions.. balancing and all..

Could someone help by

• Giving euqations like [metal+acid--> }
• Giving tips about how to go about it .
• suggesting some good sites for studying and maybe vedios?

I would like to add that I am a very good learner.. its just that I was distracted and didn't study chemistry.. otherwise I am good at studies.. so you can gie high level suggestions.. as I want to go into Non-Medical speicliasation from next year on.. and I really need to Strenthen my Phys,Chem,Maths to get into the best Engineering Colleges.. :)

[sahilmangal]

Sorry for wrong spellings I was in a little furry.. :P

[sahilmangal]

*hurry

[Unknown008]

Well, one thing at a time.

If you get familiar to the periodic table, you can easily grasp the valencies of elements. Valency is a number which indicates how a compound will be formed. You'll learn how the formula of a compound can be written from its elements using other surer methods.

For example, in the group I of the periodic table, all the elements have valency 1. Hydrogen, Lithium, Sodium, Potassium, Rubidium, etc have valency 1.

In group II, Beryllium, Magnesium, Calcium, Strontium, Barium, etc have valency 2.

In group III, Boron, Aluminium have valency 3.

In group IV, however, Carbon, Silicon, Tin and Lead has valency 2 or 4.

In group V, Nitrogen, Phosphorous have valency 3 or 5.

In group VI, Oxygen has valency 2 while Sulfur has valency 2, 4 or 6.

In group VII, Fluorine, Chlorine, Bromine, Iodine have valency 1.

So, if you noticed a pattern, from group I to group 6, the valencies increase, but at group IV, they get one or more valencies. This is a little more like a pyramid where I added the other valencies below: (They are in order of column, group I to group VII)

1 2 3 4 3 2 1
      2 5 4
          6

Knowing this will help you find formulae of compounds. For example, take common salt, which is sodium chloride.

Sodium has valency 1, chlorine has valency 1. Put the symbols of the elements one besides each other, with their respective valencies underneath. Then, 'cross multiply' the symbols with the valencies:

Na  Cl
1    1

But since the convention is metal first (or solid first, then gas element), then non metal this becomes:



And now, if you have a '1' you don't put it.



This is the formula of common salt; Sodium Chloride.

Something else now. Carbon dioxide, the gas which is the causing so much trouble about global warming. This is made up of carbon and oxygen. Here carbon takes valency 4 (which you will learn much much later why).

C  O
4  2

Again, you rearrange but since you have a common factor, you also simplify it like this:



A last one, Aluminium Oxide.

Al  O
3   2

The formula of aluminium oxide becomes:

Got it? :)
~~~~~~~~~~~~~~~
Coming to reactions now.

Metal + Acid? Okay.

Sodium + Hydrochloric acid --> ?

You should know that metals react with acids to form a salt (metal + nonmetal) and hydrogen gas.

In this case, you get sodium chloride and hydrogen gas.

Sodium + Hydrochloric acid --> Sodium chloride + Hydrogen

In symbols;



You can find the formula of HCl now, and you already found that of sodium chloride. Now, let's see if the equation is balanced.

There is 1 Na on both sides... good!
There is 1 H on the left, but 2 H on the right... not good!

What you do, is multiply the HCl by 2 so that there will be 2 H on the left:



Okay, 1 Na on both sides... good!
2 H on both sides... good!
2 Cl on the left, but 1 Cl on the right... not good!

So, multiply the NaCl on the right by 2. You'll see that you now have less Na on the left after counting all the elements. Multiply Na by 2, to get:



This time, everything is balanced!

Some other reactions now...
Magnesium + Nitric acid --> Magnesium nitrate + Hydrogen


I already balanced the equation. You'll notice that there are some 'compounds' such as 'nitrate' which have an overall valency. You'll have to learn them for the time being.



Now, can you do these?
Zinc + Hydrochloric acid --> ? (Zinc - Valency 2)
Iron + Sulfuric acid --> ? (Iron - Valency 2)
Iron + Nitric acid --> ? (Iron - Valency 3)
Copper + Nitric acid --> (Copper - Valency 2)

[sahilmangal]

:O :O
Terrified at such a nice and big answer! You are really awesome Unknown008! OMG!

Now,getting back to my question,

Metal + Acid? Okay.

Sodium + Hydrochloric acid --> ?

You should know that metals react with acids to form a salt (metal + nonmetal) and hydrogen gas.

Quite true.. But I was asking for equations like these..

for e.g.. Metal+Acid-> Salt+h2
Metal Carbonate+Acid-> Salt+h20+co2
etc etc ( some call these "skeletal equations" i.e. the basic backbone equations! )


Your answer is highly appreciable!

i would also like to ask that :
1) How to dteremine the overall charge of molecules
2)Redox reactions
3)And those elements with 2 valenices.. they are called transition elements.. right? Or isotopes? Lik Fe2 or Fe3?

:P I really got lot of doubts in Chem.. and I really HOpe AMHD would be a great resource! :)

You Rock!
Thanks!

[Unknown008]

Well,those that I can think about right now aree:

Metal Oxide + Acid --> Metal Salt + Water
Metal Carbonate -(heat)-> Metal Oxide + Carbon dioxide
Acid + Alkali --> Salt + Water

Some more advanced:
Metal (group II) Nitrate -(heat)-> Metal Oxide + Nitrogen Dioxide + Oxygen
Metal (group I) Nitrate -(heat)-> Metal Nitride + Oxygen

To find the overall charge of a molecule, you need to know about oxidation states. Like I told you before, there is something that is used rather than valencies and these are the oxidation states.

Group I metal ions have oxidation state +1 (They form singly positively charged cations)
Group II metal ions have oxidation state +2.
The valencies and oxidation states are similar, but there are positive or negative oxidation states. (as well as 0)

Group III - +3
Group IV - +2, +4
Group V - -3, +5
Group VI - -2, -4, +6

I'm running out of time right now. Got to continue later on.

EDIT: I forgot to add (heat) to the decomposition of nitrates and the Group V oxidation states are -3 and +5, not -3 and -5. I think I pressed the wrong key earlier.

[sahilmangal]

Okay sure. Do continue later! I owe a lot to you! :D

[Unknown008]

Ok, I forgot one reaction:

Metal + Water --> Metal Hydroxide + Hydrogen

Some exceptions now...
This reaction, as the reaction of metal + acid and metal carbonate will depend on the reactivity of the metal. The reactivity series (the essentials) is as follows:

Potassium
Sodium
Calcium
Aluminium
Magnesium
Zinc
Iron
Lead
Copper
Mercury
Silver
Gold

K, Na and Ca all react vigorously with cold water. K sometimes even burn with a lilac (purple) flame, sodium with a yellow flame and calcium with a brick red flame, giving KOH, NaOH and Ca(OH)_2 respectively and hydrogen gas.

Magnesium and aluminium react slowly with cold water, but violenty with steam to give their corresponding hydroxides, Mg(OH)_2 and Al(OH)_3 together with hydrogen gas. However, due to the high temperature, the hydroxide decomposes immediately to give the oxides; MgO and Al_2O_3.

As for zinc, it burns with steam, to form ZnO. The hot ZnO is yellow but white when cold.
-Tip : This colour difference might come handy when doing practicals, to identify this substance

Iron reacts slowly with hot steam forming tri-iron tetroxide and hydrogen gas. But since the tri-iron tetroxide is unstable, it decomposes back to iron metal.
- Tip: Tri iron = 3 Fe, Tetroxide = Tetra oxide = 4 O


Lead, Copper, Mercury, Silver and Gold do not react with water or steam.


With acids now.
K and Na react explosively with acids (even dilute) forming the salt and hydrogen gas.

Calcium reacts vigorously and magnesium reacts rapidly with acids to give the salt and hydrogen gas. Aluminium first react slowly, but after some time, it reacts rapidly to form the salt and hydrogen gas. This 'slow start' is due to the protective oxide coating of aluminium which reacts with the acid slowly first. When this oxide layer has reacted, then the aluminium reacts rapidly.

Zinc and iron react with acids less quickly with acids to form the salt and hydrogen gas. (To get hydrogen gas in the laboratory, Zinc is made to react with an acid, usually hydrochloric acid)

Copper, Mercury, Silver and Gold do not react with acids.
(Copper does however react with hot concentrated nitric acid, which you will learn later)


Now, the thermal decomposition of metal carbonates.
Reactive metal carbonates are stable to heat and will not decompose easily.

Na_2CO_3 and K_2CO_3 do not decompose on strong heating. The bunsen is not hot enough.

CaCO_3 decompose slowly upon strong heating.

The other metal oxides below CaCO_3 in the reactivity series decompose quite easily in a bunsen flame to give the oxide and carbon dioxide.

For metal oxides + acid, they all react... carbonates + acid they all react.

One other thing concerning the reactivity series, is displacement.
A more reactive metal will displace a less reactive metal from its salt.

e.g..


In this reaction, the blue coloured solution due to CuSO_4 fades until it becomes colourless. You will find a reddish brown (or pink) deposit on the iron that you put. This is copper metal being deposited onto the surface of the iron.
- Tip: A more reactive metal is stronger... and will steal the companion of the less reactive metal.

If you have:


You will predict that NaNO_3 and Fe are formed... but in fact, Na is so reactive that it will first react with water to give:



Then, this NaOH will react with the Fe(NO_3)_3 to give Fe(OH)_3:




Coming back to the overall charge of a molecule. A molecule by itself is never charged. It is always neutral. But there are molecular ions which exists naturally in aqueous solutions or in solids.



N has oxidation state +5 here and O has oxidation state -2.
There is one N and 3 O, so:
+5 -2 -2 -2 = -1

Hence, NO_3 has an overall charge of 1-.



S : +6
O: -2

Overall: +6 -2 -2 -2 -2 = -2

So, it becomes:

Try out for (C: +4, O: -2)


As for redox reactions, they involve a change in oxidation states of chemical species.
An atom on its own, like metals (Na, K, Mg, Fe, etc), element gases (H_2, O_2, N_2) and element solids (P_4, S_8) are all considered to be at oxidation state (also called oxidation number) zero, 0.
Otherwise, the oxidation state of an ion is given by its charge.

has oxidation state 1+.

has oxidation state 3-.

Let's take the molecular ion,

We know that the overall charge is 2-. That of oxygen is 2-. We have to find that of Cr now. Let's say, it's oxidation number is 'x'.

2x -2 -2 -2 -2 -2 -2 -2 = -2
2x - 14 = -2
2x = +12
x = +6

So, the oxidation state of Cr in is 6+.

In redox reactions, the oxidation state of elements change. One increases while another one decreases. Let's take metal + acid.



The oxidation states on the left hand side are:
Zn : 0
H : +1
Cl : -1

Those on the right hand side are:
Zn : 2+
H : 0
Cl : -1

We say that the zinc metal has reduced the Hydrogen ion because the oxidation number of the latter decreased from +1 to 0. We can also say that the Hydrogen ion has oxidised the Zn metal from 0 to 2+.

A reducing agent is one that reduces a substance with itself being oxidised.
An oxidising agent is one that oxidises a substance with itself being reduced.

Taking the displacement reactions:


Fe is oxidised to Fe^2+ by Cu^2+.
Cu^2+ is reduced to Cu by Fe

This is the basics of redox and this should enable to do do most problems on this.


Transition elements can have many different valencies, let me show you:

Sc  Ti  V   Cr  Mn  Fe  Co  Ni  Cu  Zn
                                +1
    +2  +2  +2  +2  +2  +2  +2  +2  +2
+3  +3  +3  +3  +3  +3  +3  +3  +3
    4+  4+  4+  4+  4+  4+  4+
        +5  +5  +5  +5  +5
            +6  +6  +6
                +7

As you can see, Mn has the largest number of oxidation states with up to +7! In redox, the higher oxidation number a species, the more likely it will get reduced, and so, oxidise another substance. MnO_4^-, for instance, you'll see that Mn has oxidation number +7 and is one of the most powerful oxidising agents in a common laboratory.

Phew! Questions? :)

[sahilmangal]

@Unkown008

Don't tell me that you really typed all that stuff all by yourself? :O :O.. O.M.G! A BIG one!

Its really going to take me sometime reading this.. You are totally awesome! WOW man!. I can't expres myself!

I'll study deeper into the answers you gave and then get back to my textbook.. and is it okay if I get back after a few days in this topic again? :)

[Unknown008]

No problem at all :)

Yes, I type it all by myself. The LaTeX code sure is handy to write in chemical equations :)

Plus, it's a revision for me too. I tend to forget some basic stuff which concentrating on the latest things that I learn.

But tell me, in what class are you right now? This will help me estimate where to stop, where to continue. Are you taking O-Levels? A-Levels?

For my part, I'm taking my A-Levels this year as you can see in my signature. The exams are in some 40 days! :eek:

[sahilmangal]

But tell me, in what class are you right now? This will help me estimate where to stop, where to continue. Are you taking O-Levels? A-Levels?

For my part, I'm taking my A-Levels this year as you can see in my signature. The exams are in some 40 days!

It seems we have different systems here.I belog to India.. and we don't have 'levels' here.. but we have 'classes' class 1,2,3 etc.. (each year you succeed into the next class)

I am in class 10 right now.. (15yrs :D)

But I study in the ICSE board... which is quite ahead of the normal CBSE board as followed in India.

So,virtually, you have really high levels to stop at, I have done all kind of numerical from Mole Concept, detailed study of elements like H,HCl,Nh3... and now I am studying Organic chemistry :)


And.. I would like to mention I am really going crazy to talk to you over chat or something! :P

[sahilmangal]

I would alo like to mention.. as such I;m okay in chemistry.. but from my first post in this ques you might think I'm weak.. but the thing is. Just some of the basics.. somewhere or the other are not clear.. otherwise I;'m good enough :) about what's being taught ;)

[Unknown008]

Hm... so that goes to the first year of O-Levels for me, which is three years back for me. Okay, I know where to stop.

Because if you were 17, then I'd have to talk more about redox, the equations involving and .

Okay, if you have questions, I'll do my best to answer them :)

[sahilmangal]

Hmm Okay.. I'll just keep studying and ask if I have some doubts ?

Thanks! :) I'm your fan! :D