Biology; Chemistry; Physics: Post your doubts here!

[flaminheroes]

and one more this when there is water in a electrolyte ALWAYS H+ at cathode and OH- at anode? I heard if there is a halogen then halogen is produced and not -OH is it true?

well see if the soloution is concentrated then a halogen will be released. like uh in concentrated sodium chloride, chlorine gas will be given off instead of oxygen.

 

[ZaqZainab]

no man you got it wrong. In dilute soloutions, water content is in a higher content.
Aqueous has a higher amount of water then in concentrated.

yeah but what about aqueous concentrated

 

[sadiaali]

http://papers.xtremepapers.com/CIE/...al O Level/Chemistry (5070)/5070_s07_qp_4.pdf

please anyone explain Q3 iv

 

[flaminheroes]

yeah but what about aqueous concentrated

-__- There is no aqueous concentrated.

 

[ZaqZainab]

-__- There is no aqueous concentrated.

the other way around i mean concentrated aqueous and it is there
http://papers.xtremepapers.com/CIE/...al O Level/Chemistry (5070)/5070_w03_qp_4.pdf question 3 its there

 

[robinhoodmustafa]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Chemistry (5070)/5070_s07_qp_4.pdf

please anyone explain Q3 iv

4.2 grams of CxHy Reacts with 16 gram of Br2 (we will take Br2 and no Single Br because Gas are in Diatomic Form)
and Mr of Br2 is 160 so just compare
So,

4.2g -------------- 16 g
X-------------------160

Cross multiply and answer is 42 (this is the Mr)
Now Recall that Bromine reacts with Alkene only.. So General formula of alkene is C2H2n so put Values X from 1-10 in Calculator and see the answer..
x=3
C (3) H2(3) = 42

so Its propene ( C3H6)

 

[usama321]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Chemistry (5070)/5070_s07_qp_4.pdf

please anyone explain Q3 iv

you have to remember that bromine is diatomic

so number of moles of bromine = 16/160 = .1 mole.

so 4.2g of hydrocarbon is .1 mole. so 1 mole would be 42 grams. Now, lets see, the mass of C3H6 is 42g

 

[usama321]

the other way around i mean concentrated aqueous and it is there
http://papers.xtremepapers.com/CIE/Cambridge International O Level/Chemistry (5070)/5070_w03_qp_4.pdf question 3 its there

I told you it is the same thing. lets look at the meanings of the words. Concentrated means of high concentration. Concentrated aqueous means containing high concentration of that thing in water. Usually, you can write it both ways, concentrated HCl, or concentrated aquoes HCl, it is the same thing

 

[Snowysangel]

Do transition metals give any reaction with water? And could someone tell me the observation when alkali metals are reacted with water

 

[Kamihus]

Where do we have 2 divide the mass by 2 times Ar and where by one time in calculating moles???
Sometimes diatomic gases such as oxygen r divided by just 1 Ar

 

[usama321]

Where do we have 2 divide the mass by 2 times Ar and where by one time in calculating moles???
Sometimes diatomic gases such as oxygen r divided by just 1 Ar

we do that when they are in compounds like sulfates nitrates that is when they are not in diatomic form. However lets talk about combustion, in which oxygen is in diatomic form. in those reactions, we take the mass of the two atoms

 

[Kamihus]

we do that when they are in compounds like sulfates nitrates that is when they are not in diatomic form. However lets talk about combustion, in which oxygen is in diatomic form. in those reactions, we take the mass of the two atoms

And not in hydroxides?? n what about halides, r they always divided by two

 

[usama321]

And not in hydroxides?? n what about halides, r they always divided by two

that depends. I mean when in a compound like NaCl, you will of course use mass of only one atom. But lets take this example

Cl2 + AgBr = AgCl + Br2

In this reaction if he asks about what mass would be required to displace the Bromine, i think it should be 35.5 +35.5 = 71g

 

[flaminheroes]

4.2 grams of CxHy Reacts with 16 gram of Br2 (we will take Br2 and no Single Br because Gas are in Diatomic Form)
and Mr of Br2 is 160 so just compare
So,

4.2g -------------- 16 g
X-------------------160

Cross multiply and answer is 42 (this is the Mr)
Now Recall that Bromine reacts with Alkene only.. So General formula of alkene is C2H2n so put Values X from 1-10 in Calculator and see the answer..
x=3
C (3) H2(3) = 42

so Its propene ( C3H6)

You Sir are a genius.

the other way around i mean concentrated aqueous and it is there
http://papers.xtremepapers.com/CIE/Cambridge International O Level/Chemistry (5070)/5070_w03_qp_4.pdf question 3 its there

Well i'll be damned :| Though it's actually the same as conncentrated nacl

 

[robinhoodmustafa]

You Sir are a genius.

Chemistry calculation is nothing but comparing ratio's

I hate Physic -.-

 

[flaminheroes]

Do transition metals give any reaction with water? And could someone tell me the observation when alkali metals are reacted with water

K and Na give hardcore explosive reactions.
Calcium has a voilent reaction.
mg and zinc have a moderate reactionm
and iron has a slow reaction.

 

[flaminheroes]

Chemistry calculation is nothing but comparing ratio's

I hate Physic -.-

Same D:

 

[robinhoodmustafa]

Same D:

ThankGod. I am not alone.

 

[HarithAslam]

papers.xtremepapers.com/CIE/Cambridge%20International%20O%20Level/Chemistry%20(5070)/5070_w11_qp_41.pdf
Q7, why is the answer D?

 

[robinhoodmustafa]

papers.xtremepapers.com/CIE/Cambridge%20International%20O%20Level/Chemistry%20(5070)/5070_w11_qp_41.pdf
Q7, why is the answer D?

answer is d

Calcium Carbonate is a Limiting substance so Its mass in reaction will change but the HCL Volume wont change as it is in excess