Biology; Chemistry; Physics: Post your doubts here!

[Saad Mughal]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Chemistry (5070)/5070_s08_qp_1.pdf

Same Paper. Q.33. Explain what happens through the processes please. Thanks in Advance!

The large gravel is to separate twigs and large substances.
The small sized gravel is to separate mud, sand and smaller substances.
The carbon is used to remove tastes and odor from the water.
The chlorine is used to kill bacteria.

 

[Saad Mughal]

Can you explain Reduction and Oxidation too? Please this is killing me

Remember these,
Oxidation is gain of oxygen, loss of hydrogen and loss of electrons.
Reduction is loss of oxygen, gain of hydrogen and gain of electrons.

 

[Amnaa]

Find the moles ratio using the equation.
Calculate the number of moles of each reactant by the given mass/volume.
The reactant that has the greater quantities of moles than required for the reaction (by mole:mole ratio) is in excess. The other one is the limiting agent.

i usually find moles perfecty.. but i am unable to solve with the ratioo...
like in EQ= i mol of zinc reacts with 2 mole of HCL.. and if 0.05 mol of zinc was reacte with 0.075 mol of HCl.. so which rectant will be in excess

 

[farhan141]

Okay thanks alot. Answer my other question please.

 

[Saad Mughal]

Okay thanks alot. Answer my other question please.

Which one?

 

[Saad Mughal]

i usually find moles perfecty.. but i am unable to solve with the ratioo...
like in EQ= i mol of zinc reacts with 2 mole of HCL.. and if 0.05 mol of zinc was reacte with 0.075 mol of HCl.. so which rectant will be in excess

Look at it like this,
Ratio from equation, 1 : 2,
From calculations,
1 : 2 = 0.05 : 0.075
Now, from this, we can tell that,
0.05 moles of Zn requires 0.1 moles of HCl but only 0.075 is present.
So HCl is limiting agent or you can say, Zinc is in excess.

 

[Amnaa]

in ionic bond.. every metal is combined with 6 other element?

 

[Saad Mughal]

in ionic bond.. every metal is combined with 6 other element?

It depends. If the ionic bond is NaCl, then each Na ion is attached to 4 Cl ions and the converse is also true.
In MgCl2, each Mg ion is attached to 6 Cl ions.
And so on,
But we don't have to study structures of the complex lattices.

 

[Amnaa]

in metals.. free electrons are responsible for the transfer of heat and electricity?

 

[Saad Mughal]

in metals.. free electrons are responsible for the transfer of heat and electricity?

Yeah.

 

[Amnaa]

should i study the endothermic and exothermic reaction.. or there is any clue to observe frm the equation?

 

[Amnaa]

Yeah.

and ions in ionic bond and in molten solution..?? and electrons in covalent bond??

 

[Saad Mughal]

should i study the endothermic and exothermic reaction.. or there is any clue to observe frm the equation?

You should know the basics, such as photosynthesis, dissolving, neutralization, combustion, thermal decomposition.

 

[Saad Mughal]

and ions in ionic bond and in molten solution..?? and electrons in covalent bond??

Ions conduct electricity in Ionic bonds.
Covalent compounds are not good conductors of heat and electricity because they have no free electrons.

 

[Amnaa]

NAHI...

You should know the basics, such as photosynthesis, dissolving, neutralization, combustion, thermal decomposition.

NAHI... :/ yaad hy to nah hota :S

 

[Saad Mughal]

NAHI...
NAHI... :/ yaad hy to nah hota :S

It's pretty easy,
Photosynthesis, Dissolving, Thermal Decomposition - Endothermic.
Neutralization, Combustion - Exothermic.

 

[Amnaa]

Okay... i have more questions..
look if there is given that X element have b.p and m.p.
how would i come to know its state rtp?

 

[Amnaa]

H2+O2---H2O..
is this reaction is enodthermic or exothermic

 

[Saad Mughal]

Okay... i have more questions..
look if there is given that X element have b.p and m.p.
how would i come to know its state rtp?

20 deg. C is room temperature.
If melting point and boiling point is below this then it is a gas,
If boiling point is above and melting point is below this then it is a liquid,
If both melting and boiling point are above this, it is a solid.

 

[Saad Mughal]

H2+O2---H2O..
is this reaction is enodthermic or exothermic

It's exothermic.