CHEM AND BIO HELP AND TIPS HERE

[rameeziiii]

ok its like this Si + 2F₂.... 7.2 grams= 7.2/38...(not 19 as it is the gas molecule not the atom)
so it becomes 0.189.... now since Si needs 2 moles of F₂ 0.08 moles needs 0.16 moles but F₂ has 0.189 and therefore Si is the limiting agent

[sarasa]

can anyone pls ans my question... 

Ok calculate da no. of moles of Br2= 25 divided (80*2)= 0.156
then takin da ration Si: Br2 is 1:2 so if silicon is 0.07 then Br2 should be double it that is 0.14
but the real amount is 0.156 which is greater than 0.07 so bromine is in excess nd Silicon is da limiting reagent
Hope I helped
My answer is for da first variant

[$H00t!N& $t@r]

MJ04  Q4 how do i know  what salt to use, what cant it be a zinc oxide or hydroxide for preparing an insolubles salt?

I'D LIKE A REPLY! theres been like 3 replies AFTER my post ,but no rresonse to my post!

precipitation method uses two solubles to form an insoluble base
hydroxides are insoluble (except those of ammonia, barium and alkali metal (group 1) cations) so we cant use that
all oxides are also insoluble (except those of calcium, barium and alkali metal cations) so we cant use these either

we have to choose a soluble base. we can use chlorides as they are soluble. therefore zinc chloride+ sodium carbonate= zinc carbonate+ sodium chloride

Im not quite sure of my answer though. can some1 pls confirm

[$H00t!N& $t@r]

thnku both for the answer!
i actually got the right answer but i was looking at the markscheme for a different variant! silly me! 
anyway Thanks guys!

[rameeziiii]

precipitation method uses two solubles to form an insoluble base
hydroxides are insoluble (except those of ammonia, barium and alkali metal (group 1) cations) so we cant use that
all oxides are also insoluble (except those of calcium, barium and alkali metal cations) so we cant use these either

we have to choose a soluble base. we can use chlorides as they are soluble. therefore zinc chloride+ sodium carbonate= zinc carbonate+ sodium chloride

Im not quite sure of my answer though. can some1 pls confirm

yeah its correct... although you could use sulphate or nitrate... both are soluble

[rameeziiii]

Umm...could someone tell me WHY increasing pressure favors the RHS of equation in gases... why it moves equilibrium to right

[Raywin]

Umm...could someone tell me WHY increasing pressure favors the RHS of equation in gases... why it moves equilibrium to right

An increase in pressure, decreases the volume for the forward reaction. Thus, the chances of an effective collision of the particles are more since the volume decreases. So, since the chances of the collisions in the forward reaction is more, it favors the RHS of the equation, this moves the equilibrium to the right. hope you got me.

[JD46]

Increasing pressure favours the side which has fewer gas molecules or moles ,as a result the right hand sides  will produce more gas mols,=higher  yield!

[MasterMath]

I haveee justtt one question ..there is this question about using Calcium carbonate instead of calcium oxide .. I know that calcium carbonate is not soluble so it remains longer in soil.. but they say in MS .. that calcium carbonate the Ph cant go above 7 , but with calcium oxide it can go.. i dont get that part.. thanks in advance!

[JD46]

 u answered you own  question!!
 due to its property to noe dissolve in excess watering,rain, caco3 will not make the soil alkaline,on the other hand Cao is  soluble to some extent and willl make the soil  alkaline in PH

[Vin]

Umm...could someone tell me WHY increasing pressure favors the RHS of equation in gases... why it moves equilibrium to right

okay, image the pivot and scale as in physics.. reaction of N2 + H2 as an example..
 ____                          _____
| N2|                          |     |
|H2  |                         |NH3|
------                         |      |
-------------------------------
                    |

Always when a reversible reaction is in equilibrium and you make a change(inc/dec. pressure/temp), it will do what it can to oppose the change.

Temp::Increase the temp. the heat will be used to both for forward as well as the backward reaction. Forward: N2 and H2 combine, backward:heat used to break NH3 to form. This is a state of dynamic equilibrium.

Pressure::Increase the pressure(by adding more N2 and H2), the mixture will act to oppose the change and eliminates these molecules by combining them to form NH3 so the equi. shifts to the right..

[MasterMath]

u answered you own  question!!
 due to its property to noe dissolve in excess watering,rain, caco3 will not make the soil alkaline,on the other hand Cao is  soluble to some extent and willl make the soil  alkaline in PH

but hmm... How does it neutralize the acidity of the soil without increasing its Ph >_< ?
I got what you mean but im a bit confused

[MasterMath]

but hmm... How does it neutralize the acidity of the soil without increasing its Ph >_< ?
I got what you mean but im a bit confused

You mean when you add either of them .. they react with the acidic parts or w.e and then just stop reacting unless they disolve ..? and when they disolve they would obviously make it Ph>7 ?

[nid404]

I haveee justtt one question ..there is this question about using Calcium carbonate instead of calcium oxide .. I know that calcium carbonate is not soluble so it remains longer in soil.. but they say in MS .. that calcium carbonate the Ph cant go above 7 , but with calcium oxide it can go.. i dont get that part.. thanks in advance!

Carbonate is a salt...so it's pH is neutral
whereas oxide of group 2 metals are alkaline.

[JD46]

Could someone  scan their guide,or click a pic or anything,but post it up here,this is about chemistry excess reagents, could you scan the part in bob berry's guides and put it up here Pg 33 -34 i thnk as you can see many  people are having doubts bout the reagent stuff!! so this time around someone DO STH!! the last i got NO RESPONSE!,it will benefit lots of people