albertlee

I always wonder why this happens...

if I place a cup of water on the table, after a very long time, the water is gone...

why's that? why doesn't it remain liquid water?

Wow...

does silica have high melting point?

It looks to me as an ionic compound...

btw, are all crystals covalent?

We know that carbon always exist in covalent bond with itself or other elements.

But, how about Silicon? is silica a convalent or ionic compound?

Well, I actually have my proof, but I dont know whether you can call it a proof or not.

Say, a>b,

(a+b)/2 must be the center point between a and b, right? let's call this point c.

(a+c)/2 is the point between a and c, which is also a point between a and (a+b)/2, so--> (a+[(a+b)/2])2, call this point d.

Then we can also find a point between a and d.

(a+d)/2, which is also (a+(a+[(a+b)/2])2)/2

etc etc, the above sequence can go as follow in simplfied:

1, (a+b)/2

2, (a+(a+b)/2)/2 --> (3a+b)/4

3, (a+(3a+b)/4)/2 --> (7a+b)/8

4, (15a+b)/16

5, (31a+b)/32

...

so, the formula of such sequence is:

((2ⁿ-1)a+b)/2ⁿ

therefore, there exists infinite rationals between any two points a and b.

Is this a good proof?

proove that between any two points a and b, a!=b, on the x axis, there are infinitely many rational points.

How do you solve the above? I know it's simple, but I just cant put down mathematically.

please help

thanks

Has any one used NetBeans before??

Is my question that hard????

package supershare;

 

import java.awt.event.*;

import javax.swing.*;

 

public class testGUI extends javax.swing.JFrame implements java.awt.event.ActionListener{

 

 

public testGUI(){initComponents();}

 

public void initComponents(){/*Generated Code*/}

 

public static void main(String args[]) {

 

new testGUI().setVisible(true);

 

}

public void actionPerformed(ActionEvent e)

{

/*JProgressBar jp = new JProgressBar(0' date=' 100);

jp.setValue(0);

jp.setStringPainted(true);

 

this.add(jp);

this.validate();*/

 

this.remove(jButton1);

this.validate();

this.repaint();

}

// Variables declaration - do not modify

private javax.swing.JButton jButton1;

// End of variables declaration

 

}

 

[/quote']

 

 

Above is the code I made under NetBeans....

 

As you know, NetBeans has a function called "JFrameForm", which allows you to design GUI more conviniently....

 

if you are familar with NetBeans, you can easily understand the above code...

 

You know what I am trying to do is that when I click the button, the button should disappear, but it doesnot....

 

please help here... actually, I have a bigger project meeting this problem.. and if I have to design the whole project without using NetBeans's JFrameForm function, it will be a nightmare...yes, lots of work...

 

 

Apreciate any help

 

thanks

However, if the water is evaporated away, the iron hydroxide rearranges itself and forms iron-oxide with molecules of water trapped inside the crystal structure. This is what we call rust.

oh yeah..

btw, I have seen rust formed by iron in water, without evaporating the water..

what's the chemistry here apart from the above quote??

thanks alot

Virtually ALL gases are more soluble in cold water than hot water. That's why we keep soda pop in the fridge. This is because gases dissolve as a result of very weak intermolecular forces between the gas and the water. Remember, electrons are NOT static creatures. They are constantly moving around the gas molecules resulting in partial charges forming here and there. These partial charges allow the gas to gain momentary attractions to the water molecules and allows it to dissolve in the water. At low temperatures, the water molecules aren't moving around as much so the gas molecules are constantly surrounded by the charged water molecules. In higher temperature water, the water molecules move around at a MUCH greater rate which cuts back on the amount of time the gas molecule is 'stabilized' by the polar water molecules. As a result, the solubility is not nearly as great.

but, why sugar dissolves better in warmer water?

thanks Jdurg

How is oxygen dissolved in water??

Since oxygen is neutral, ie, formed by covalent bond, it shouldn't have any charge, right??

from wikipedia

When steel contacts water, an electrochemical process starts. On the surface of the metal, iron is oxidised to iron(II):

 

Fe → Fe2+ + 2e-

Can any one just explain how the above happens in rusting?? ie, what is the electrochemical process here? What does it have to do with electrochemistry??

Can any one please help here.....

thanks

any one can help me according to post #7?

oh... please help...

Am I asking something nonsense??

please help...

thanks

so what element/molecule/compound attracts the electrons of iron in the 1st place during rusting??

I mean, the OH- ions should not be the factor, because it does not need more electrons...

what is wt. %?

and again, any one can help me according to post #7?

ok... this question has nothing to do with my last question here...

First we know that iron must be oxidized,

Fe + H2O -> FeOH + H2 (not balanced)

However, is it OH- ion that cause Fe to loose its electrons??

OH- already has excess electron, therefore it must be the H+ ion which causes Fe to loose electron

so, the oxidizing agent is actually H+ ions, right??

like this: Fe + 2H+ --> Fe2- + H2

2nd question: If there is no oxygen in water, does Iron still form iron hydroxide?? because in reality, I never see what does iron hydroxide look like....

any help??

thx alot

YT, I think iron is not a very reactive metal, you might need to heat the whole thing up.

Cheers

the thing is,

1M = 1mole of acid molecules / 1L of water

To me, there is no % here, because you can have 1M, 2M, 3M, ...nM...

by the way, please also help me from the the post #7...

thx alot

Fe(s) + H2SO4(aq) -> Fe(II)SO4(aq) + H2(g)

how does H2 exist as positive ion??

is it a diatomic ion or as a single atom ion in the solution??

thx alot

btw, I always find hard to tell the concentration of acid/alkali in %.

Say 1M of acid in water, what is its concentration in %?

btw, I always find hard to tell the concentration of acid/alkali in %.

Say 1M of acid in water, what is its concentration in %?

An example of inappropriate use of this forum: You ask something about hydroxide in acid. You get a good answer and now in your followup you suddenly ask a question about solubility of oxygen. This behavior does not really give us the impression that you think over the answers you obtain and just shoot out random questions.

Why do you think that I didnot think over the answers?

aren't both questions related to "concentration of particles in a solution"?

all questions actually related to an investigation I did about iron rusting under different pH.

there are five sets of iron nail in testtube with different solution, and each of them is sealed with a stopper.

1, sulfuric acid 1/3M

2, sulfuric acid 2/3M

3, Sodium Hydroxide 1/3M

4, Sodium Hydroxide 2/3M

5, tap water

This is what I found out,

the rusting of nail under tap water is the greatest, the weaker Alkali is the second greatest, but only a little bit of rust.

For the stronger acid, the nail turns completely black and for the weaker one, the nail is corroded to an extent that it becomes black powders.

for the stronger alkali, nothing happens to the nail.

This actually contradicts to what I thought in the beginning. I thought that alkali will increase the rate of rusting....

So I conclude that it must be the alteration of concentration of oxygen, which means that maybe there is less oxygen in alkali than in water, when the tube is sealed.

The other thing goes out of expectancy is the acid, how come the weaker acid actually corrodes more??

Any help on this??

thx alot

I am abit confused about what do you mean by "pure"...

pure acid does contain water, therefore it has OH- ions in it.

Secondly, how do you find out how much oxygen is dissolved in a solution??

please help

thx alot

Even acid has OH- ions in it...., but how can we measure how many OH- ions there are...

secondly, how can we determine how many ions/molecules a solution can dissolve?? esp with water as the solvent. Eg, how many oxygen molecules, hydrogen ions, halogen ions, etc... can water dissolve?

Any help??

thx alot