Physics, Chemistry and Biology: Post your doubts here!

[joulie]

can u help me in this biology may june 2010 Q 35 why will the carbon dioxide help soybeans to grow ???

 

[always-smile :)]

can u help me in this biology may june 2010 Q 35 why will the carbon dioxide help soybeans to grow ???

cause it will have more CO2 to make more photosynthesis

 

[always-smile :)]

pllz another stupid question
winter 2007 no.1 (( why its evaporation not diffusion ))

 

[joulie]

is neurone a tissue or organ ??
and is a vein an organ ??

 

[Yousif Mukkhtar]

Guys I got a doubt in q 3:
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w08_qp_1.pdf

 

[Yousif Mukkhtar]

pllz another stupid question
winter 2007 no.1 (( why its evaporation not diffusion ))

They said moves from a region of higher to lower concentration so it is definitely diffusion.

 

[Ahmed Khider]

is neurone a tissue or organ ??
and is a vein an organ ??

They both are tissues becoz they r both made of cells with similar functions. For eg a neurone is made of up similar functioning nerve cells.

 

[kainat husain]

13 : Metals form at cathode as they form positively charged ions so they attract to the negative electrode so X & Y will be formed
19 : Adding in excess doesnot effect the oxidation state , but the pH increases because KOH is added in excess and it's basic so the pH becomes alkaline
22 : This is neutralization , we use the metal in powdered form i.e solid
29 : Forms an alloy can be C, Cu or Zn
Forms basic oxide can be Cu Or Zn
Below hydrogen is only copper (Reactivity series: K Na Ca Mg Al (C) Zn Fe Sn Pb (H) Cu Ag Au Pt)
30 : Refer the reactivity series Xis after Hydrogen in the series so it cannot displace hydrogen & it is below carbon so carbon CAN displace Xoxide
38 : Petroleum is a mixture of hydrocarbons , Methane is not a mixture , it is a hydrocarbon
39 : Ethene is a gas and has double bond (unsaturated) so B

thank you soooooo much for ur effort i understood

 

[kainat husain]

q13- X n Y react wid Br n O2, which will ALWAYS go to d anode, so u can make out dat x n y will go 2 d cathode

q 19- i think so:: u can't change d oxidation state, which is a chemical property, by adding xtra base. n potassium hydroxide is base coz it's "hydroxide", so pH increases. bases: CO3 ion(carbonates), OH(hydroxides), O(Oxides), hydrogencarbonates(dunno how dat appears)

q22-maybe coz they've 2 b added in xcess, so it'll b easier dat way. i think so, k, im not sure

q29- it 4ms a basic oxide, must b a metal. is below H in d reactivity series, so dat leaves only Cu. if u wanna learn d reactivity series dere's a good link http://www.bbc.co.uk/schools/ks3bit...al_behaviour/compounds_mixtures/revise5.shtml, if u haven't learnt it already, of course. H is btwn lead n copper{wikipedia}

q30- x is after H so will not displace d H 4m HCl. u noe dat Fe compound can b reduced by C, so even X will b reduced by C.

q38- mixture of hydrocarbons, so it's not methane coz methane is only a SINGULAR hydrocarbon, not a MIXTURE, which is d case wid petroleum.

q39- ethene has only 2 C atoms, so it's got a low boiling pt. u noe dat methane is gas at rtp, so even ethene will b gas
then its not saturated coz its an "ene", 4m alkene, which are an unsaturated family.

THANK U SOOOOOOOO VERY MUCH for your help

 

[Yousif Mukkhtar]

Guys I got a doubt in q 3:
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w08_qp_1.pdf

Anyone?

 

[always-smile :)]

Anyone?

i have the same doubt

 

[Ahmed Khider]

Anyone?

It is a tricky question i admit. I think u know that Barium Nitrate is soluble so Barium will dissolve in the nitrate solution leaving iodine to react lead forming lead iodide which is yellow to precipitate downwards so the ans is b..If u dnt understand feel free to ask again.

 

[Razo513]

Guys I got a doubt in q 3:
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w08_qp_1.pdf

it's B why? to get rid of the I- u have to change it to a precipitate which can only be achieved if u add aqueous lead(II) nitrate so u eliminate C &D u r left with A&B if u remember the ions test which u prepared for p6 then u will recall that I forms yellow precipitate with aqueous lead(II) nitrate

 

[always-smile :)]

It is a tricky question i admit. I think u know that Barium Nitrate is soluble so Barium will dissolve in the nitrate solution leaving iodine to react lead forming lead iodide which is yellow to precipitate downwards so the ans is b..If u dnt understand feel free to ask again.

plz i didn't get it

 

[Ahmed Khider]

plz i didn't get it

Ok heres another way to explain it. The question said a solution contains barium iodide. To obtain a solution that contains Ba2+(aq) we have to add any nitrate because u know that all nitrates are soluble so the answer is either A or B. Then when we add the nitrate(lead nitrate) the lead displaced from it will react with the iodide displaced from the older compund(barium iodide) leaving Lead Iodide which is yellow so the answer is B. If u dnt understand ask again

 

[always-smile :)]

Ok heres another way to explain it. The question said a solution contains barium iodide. To obtain a solution that contains Ba2+(aq) we have to add any nitrate because u know that all nitrates are soluble so the answer is either A or B. Then when we add the nitrate(lead nitrate) the lead displaced from it will react with the iodide displaced from the older compund(barium iodide) leaving Lead Iodide which is yellow so the answer is B. If u dnt understand ask again

thnx a million i got it

 

[joulie]

plz help in biology november 2004 Q 8
why the answer is organ system i mean isnt it supposed to be organ as each vein an artery is a tissue so they all make an organ not an organ system

 

[Ahmed Khider]

plz help in biology november 2004 Q 8
why the answer is organ system i mean isnt it supposed to be organ as each vein an artery is a tissue so they all make an organ not an organ system

It is an organ system becoz the organs shown like the stomach and the kidneys are all part of the same organ system.

 

[always-smile :)]

plz help in biology november 2004 Q 8
why the answer is organ system i mean isnt it supposed to be organ as each vein an artery is a tissue so they all make an organ not an organ system

look at the image the heart is there 2 so viens and arteries are part of the same oran system ( talking about the circulatory system all ) .... if u didn't got it ask again

 

[Yousif Mukkhtar]

Yes, I got it. It is not so difficult after all. So lead iodide is insoluble?