Biology; Chemistry; Physics: Post your doubts here!

[usama321]

I usually get no more than 30

practice past papers, and try to understand the concept behind the ones you do wrong

 

[papajohn]

practice past papers, and try to understand the concept behind the ones you do wrong

Arrrr!

 

[chocolate_girl]

Can someone please tell me what exactly oxidation state is with an example

 

[chocolate_girl]

Also please tell me the method of making ionic equations! I just cannot get them right

 

[lklk123]

Also please tell me the method of making ionic equations! I just cannot get them right

Ikr.. Me too

 

[AhsanAfzal]

why is the answer A?

 

[usama321]

Can someone please tell me what exactly oxidation state is with an example

oxidation state is well, the oxidation number of an element, when they make an ion. for example we say that Na has an ion of +1 when it gives one electron, so we will say it has an oxidation state of +1. Similarly, as some transition elements have more than 1 ion e-g Fe 2+ and Fe 3+ the first one has oxidation state of +2 and the second one +3. In compounds, the overall oxidation state is always 0 e-g MgO. The Mg has oxidation state of +2 and O has -2.

 

[usama321]

lets look at the other options

B NH3 to NO. The oxidation number in the NH3 of nitrogen is -3, while in the second one it is +2, thus it has been oxidised.
C S to H2SO4. the oxidation state increases from 0 to +6, so it has been oxidised.
D ZnS to Zn. Well in the first one its oxidation state was +2, but later reduced to 0, so reduction has taken place


now to A.
NH3 + H2SO4 = (NH4)2SO4
i am not completely sure about this, can anyone confirm it

the oxidation state of N in the reactants is -3, and that of H is +1. Now in the products, Nitrogen still has oxidation state of -3, and hydrogen still has +1, resulting in the overall charge on the NH4 ion being +1. The charge on S and O is same too on both sides

 

[chocolate_girl]

oxidation state is well, the oxidation number of an element, when they make an ion. for example we say that Na has an ion of +1 when it gives one electron, so we will say it has an oxidation state of +1. Similarly, as some transition elements have more than 1 ion e-g Fe 2+ and Fe 3+ the first one has oxidation state of +2 and the second one +3. In compounds, the overall oxidation state is always 0 e-g MgO. The Mg has oxidation state of +2 and O has -2.

Thanks alott ) would you please solve my other problemm 2! How do we make ionic equations

 

[usama321]

Thanks alott )

also remember that an element always has an oxidation state of 0...... H2, Cl2, S, etc all of them have 0 state, when they are elements and not ions

 

[AhsanAfzal]

great which year though, 2008 or 2005?

2005

 

[AhsanAfzal]

lets look at the other options

B NH3 to NO. The oxidation number in the NH3 of nitrogen is -3, while in the second one it is +2, thus it has been oxidised.
C S to H2SO4. the oxidation state increases from 0 to +6, so it has been oxidised.
D ZnS to Zn. Well in the first one its oxidation state was +2, but later reduced to 0, so reduction has taken place


now to A.
NH3 + H2SO4 = (NH4)2SO4
i am not completely sure about this, can anyone confirm it

the oxidation state of N in the reactants is -3, and that of H is +1. Now in the products, Nitrogen still has oxidation state of -3, and hydrogen still has +1, resulting in the overall charge on the NH4 ion being +1. The charge on S and O is same too on both sides

i have got it.
equation for the reaction is NH3 + H2SO4 = (NH4)2SO4+ H2O. ionic equation for all neutralization reactions= H+ + OH- =H2O. So there is no change in oxidation state of ammonia

 

[AhsanAfzal]

shouldnt answer be C? marknig scheme says D.

 

[usama321]

i have got it.
equation for the reaction is NH3 + H2SO4 = (NH4)2SO4+ H2O. ionic equation for all neutralization reactions= H+ + OH- =H2O. So there is no change in oxidation state of ammonia

nope, there would be no water, it is not titration, the ammonium salt would be the only product. Funny thing is, if water had been formed, it would have been a redox reaction

 

[AhsanAfzal]

nope, there would be no water, it is not titration, the ammonium salt would be the only product. Funny thing is, if water had been formed, it would have been a redox reaction

why? NH3 is alkaline and and H2So4 is acidic they would neutralize each other..... maybe

 

[AhsanAfzal]

nope, there would be no water, it is not titration, the ammonium salt would be the only product. Funny thing is, if water had been formed, it would have been a redox reaction

it would be a redox but ammonia's oxidation would not change

 

[AhsanAfzal]

.... but i think i am wrong

 

[usama321]

why? NH3 is alkaline and and H2So4 is acidic they would neutralize each other..... maybe

thing is it does not have OH ion even though it is basic......... NH3 reacts with acids to form fertilizers mostly.......... no water though

 

[usama321]

it would be a redox but ammonia's oxidation would not change

the mcq does not specifically ask about ammonia, it just asks about redox reaction as a whole. I assure you though, there is no oxidation reduction in this reaction, check the oxidation states yourself i was confused about it too

 

[AhsanAfzal]

anyway, whats the answer to the other question. aquatic plant dont die without oxygen. they can produce it themselves but when aquatic plant die bacteria decompose them by aerobic respiration and oxygen decreases.