Friday, February 20, 2009

Do u kNow????

How Many Bananas Does It Take to Poison You?
Thursday February 19, 2009
You probably know too much water and too many apple or cherry seeds can kill you, but did you know eating too many bananas may lead to an early demise? It's not their high radiation signature. It's because bananas contain potassium. But wait, you may be saying, isn't potassium good for me? It is, but like everything else, too much potassium is bad for you. Too much potassium can lead to heart damage and cardiac arrest. I was reminded of that when reading about an upcoming attempt to set a new world record for eating bananas. Apparently the world record effort has been scaled back so that it involves more people eating bananas and not people eating as many bananas as possible. The reason for the change was to prevent health problems or death from over-eating bananas. I couldn't help but wonder exactly how many bananas you would have to eat in order to ingest a dangerous amount of potassium. I mean... what are we talking about here? Three bananas? Ten? I have a friend who ate 7 bananas as part of some weird man-challenge. He isn't dead and didn't go into cardiac arrest, but he assures me that is nearing the upper limit of banana-eating. How many bananas do you think it takes to poison you with potassium?

Tuesday, February 17, 2009

Calculating mass or volume of a substance from a chemical equation

Here might be a little difficult for you, but I would say, Don't give up!!!
e.g. When 4g of Magnesium reacts in oxygen gas, magnesium oxide will be produced. Calculate the mass of magnesium oxide produced?
[Mg=24, O=16]
Firstly, you have to write out the equation....
Mg + O2 --> MgO
Next, check if the equation is balanced or not... Looks like it is not balance.. so, BALANCE it now!
you should get...
2Mg + O2 --> 2MgO
Now we can start our calculation... given is 4g of magnesium... so we need to calculate the mole value for Magnesium...
Mole = Mass / RAM or RMM
mole = 4g/24 and you'll get 0.1667 mole
Now you have to refer to your balanced equation...
2 mole of Magnesium will produce 2 mole of Magnesium Oxide
therefore, 0.1667 mole of Mg will also produce 0.1667 mole of MgO

The final step now is to convert the mole value of MgO to mass...
mole = mass / RAM or RMM
Mass= mole X RAM or RMM
= 0.1667 X [24 + 16]
= 0.1667 X 40
= 6.6667g
= 6.67g
** leave your answer in 2 decimal places...
Q: What is the mass of copper oxide that will be needed to produce copper when it is reacted with hydrogen gas?
[Cu=64, H=1, O=16]

Balancing Chemical Equations

Balancing a chemical equation is a very important knowledge in chemistry. What u need to do when u have to balance a chemical equation?
e.g. Al + CuO --> Al2O3 + Cu
Now the equation is not balanced.. Firstly U have to know how many Al atoms are on your left? Only 1 but you have 2 Al atoms on your right.. so u put a no 2 infront of Al...
2Al + CuO --> Al2O3 + Cu
Now u find that the number of oxygen isn't balance.. so you'll have to do something.. you can add the no 3 to CuO so that you have 3 oxygen atoms...
2Al + 3CuO --> Al2O3 + Cu
Problem now is... you have 3 Cu atoms on your left but only 1 Cu atom on your right... to make it balance, you can add the no 3 to Cu...
2Al + 3CuO --> Al2O3 + 3Cu
Now you hae a balanced equation... It is not that difficult right... try this and tell me your answer:
a) H2 + O2 --> H2O
b) Fe + Cl2 --> FeCl3
c) KMnO4 + HCl --> KCl + MnCl2 + H2O + Cl2
Good Luck :D

Saturday, February 14, 2009

How Was the TRIP?

Hi boys & girls....
I hope u gained something & learnt something 4rm the trip besides beaches, 1B and etc.. I, myself learnt a lot.. never seen so many things when I was in school or University.. U all r so gifted hehe... I hope U'l had benefited fr this trip.. Tq foe behaving well tru out the trip.. Cheers!!!

Friday, February 6, 2009

Mac Monthly Test...

10 Objective questions...(10marks X 3 = 30marks = 30%)
(7 from chapter 2 & 3 from chapter3)

3 Structure questions (30 marks X2 = 60marks = 60%)
(1 from chapter2 & 2 from chapter 3)

Online discussion (10marks=10%)
[January-February discussions]

Tuesday, February 3, 2009

Why people mix vinegar&bleach???

If mixing bleach and vinegar releases toxic chlorine gas, then why do people do it? There are two answers to this question. The first answer is that vinegar lowers the pH of bleach, making it a better disinfectant. I'll explain how that works in a bit. The second answer to 'why people mix bleach and vinegar' is that people don't know any better or underestimate the risk. They hear mixing the chemicals makes them better cleaners and disinfectants, but don't realize it isn't going to make enough of a difference to justify the considerable health hazard.

What Happens When Bleach and Vinegar Are Mixed
Chlorine bleach contains sodium hypochlorite or NaOCl. Because bleach is sodium hypochlorite in water, the sodium hypochlorite in bleach actually exists as hypochlorous acid:
NaOCl + H2O ↔ HOCl + Na+ + OH-
Hypochlorous acid is a strong oxidizer. This is what makes it so good at bleaching and disinfection. If you mix bleach with an acid, chlorine gas will be produced. For example, if you mix bleach with toilet bowl cleaner, which contains hydrochloric acid:
HOCl + HCl ↔ H2O + Cl2
Chlorine gas attacks mucous membranes, such as your eyes, throat, and lungs and can kill you, so causing that reaction isn't in your best interest. If you mix bleach with another acid, such as the acetic acid found in vinegar, you get essentially the same result:
2HOCl + 2HAc ↔ Cl2 + 2H2O + 2Ac- (Ac : CH3COO)
There is an equilibrium between the chlorine species that is influenced by pH. When the pH is lowered, as by adding toilet bowl cleaner or vinegar, the ratio of chlorine gas in increased. When the pH is raised, the ratio of hypochlorite ion is increased. Hypochlorite ion is a less efficient oxidizer than hypochlorous acid, so some people will intentionally lower the pH of bleach to increase the oxidizing power of the chemical, even though chlorine gas is produced as a result.

What You Should Do Instead
Don't poison yourself! Rather than increasing the activity of the bleach by adding vinegar to it, just buy fresh bleach! Chlorine bleach has a shelf life. This is particularly true if your bleach has been hanging around for several months. It's far safer for you to buy fresh bleach than to risk releasing a chemical weapon on yourself by mixing bleach with another chemical. You can use bleach and vinegar for cleaning, just make sure you rinse before switching products!!!