very trivial question: (1 Viewer)

[underthesun]

Was looking back at my half-yearly, and there was this question :

"Of the following, the REDOX reaction is:-"

and the answer is..

"A. dissolving sodium metal in water"

the other answers were

B. dissolving common salt in water
C. adding sodium chloride to silver nitrate solution
D. adding sodium hydroxide to hydrochloric acid

now, i must have done some elimination tactic, but im still quite curious. How is dissolving sodium metal in water a redox reaction? Have no idea where the loss of electron is and where the reduction is..

 

[iambored]

umm i dunno, have u tried writing out the equation 2 c the loss of electrons? i'm 2 lazy 2 do it atm

 

[underthesun]

that's the problem, i dont know how did they lose the electrons..

I thought you were bored? won't you mind feeling a bit adventurous and try it out?

 

[forsaken_99]

The sodium metal had an oxidation state of 0, but after it was added to the water it had an oxidation state of +1, thus redox has occured oxidation states were changed.

Hope that helped.

 

[underthesun]

That makes sense for the changing oxidation state, but how were the electrons lost, and where's the reduction?

Anyhow, it seems that I've confirmed that this is indeed not a teacher mistake, and will proceed in life knowing that this is true. thanks anyways

 

[BlackJack]

Properly, the reaction is:

2 Na(s) + 2 H20 -> 2 Na+ + 2 OH- + H2(g)

 

[spice girl]

Na(s) -> Na+ + e- (oxidation of sodium)
2H2O + 2e- -> 2OH- + H2(g) (reduction of protons in water to form H2)

 

[jims]

would help if i knew subscripts but anyway...

Oxidation: 2Na <-> 2Na(+) + 2e(-)

Reduction: 2H2O + 2e(-) <-> H2 + OH(-)

Net: 2Na + 2H2O <-> H2 + OH(-) + 2Na(+)

 

[BlackJack]

. That was almost simultaneous.

 

[underthesun]

ah, i get it now. thanks

 

[xiao1985]

the question is still weird tho i fink..... cuz u normally talk bout dissolvin interms of breakin ionic bonds, so normally u r talkin bout a physical reaction, instead of a chemical one.......... however, among the four, i fink A is most correct, but technically speakin..... dunt fink so

 

[wogboy]

Actually A) is a chemical reation (not physical reaction) because the sodium metal is not merely dissolving into the water, as say NaCl (table salt) would.

When NaCl dissolves in water, only the ionic bond between Na+ and Cl- breaks and these ions are separated in the water, so there's no chemical reaction only a physical reaction. However, when sodium metal is "dissolved" in water ("dissolve" is a misleading word, perhaps a better word is "react"), sodium metal (Na) reacts with water (H20) to form hydrogen gas (H2) and sodium hydroxide (NaOH). So there's definitely a chemical reaction going on.