Biology; Chemistry; Physics: Post your doubts here!

[multixamza01]

Chemistry 5070_w11_qp_11.
Q. 29 Which equation shows a reaction that would actually take place?
A 2MgO + C → CO2 + Mg
B MgO + Cu → CuO + Mg
C PbO + Zn → ZnO + Pb
D ZnO + H2 → H2O + Zn

The answer in the marking scheme is C. And i get it. But seeing that H2 can displace elements below Aluminium from their compounds , the answer D is also correct. Can anyone explain why the answer C is chosen and D is discarded?

 

[Nibz]

Because Hydrogen comes below Zinc in the Reactivity Series, it cannot reduce Zinc.

 

[Duanoor]

Chemistry 5070_w11_qp_11.
Q. 29 Which equation shows a reaction that would actually take place?
A 2MgO + C → CO2 + Mg
B MgO + Cu → CuO + Mg
C PbO + Zn → ZnO + Pb
D ZnO + H2 → H2O + Zn

The answer in the marking scheme is C. And i get it. But seeing that H2 can displace elements below Aluminium from their compounds , the answer D is also correct. Can anyone explain why the answer C is chosen and D is discarded?

because hydrogen comes below than zinc in reactivity series,it can not displace it...

 

[Duanoor]

AOA...i am new to xtreme papers forums...i gave o levels exams last year...will try to answer ur questions whole heartedly...i appreciate ur efforts...keep it up

 

[abcde]

can anyone solve the q.1View attachment 3851

AoA!
Heat is applied at two different points. When heat is applied at the bottom, liquid molecules gain K.E and move further apart, forming an area of low density water. The colder liquid above it has higher density so it moves downwards and is replaced by the less dense liquid. A conventional current is set up, causing the ice to melt quickly.
When heat is applied at the top of the test tube, a conventional current isn't set up because the low density water is already at the top most position. Heat reaches the ice at the bottom via conduction, which is a slower process as it does not involve the bulk movement of water molecules. So the ice melts slowly.

 

[ashfaaq7]

Studies are still taking place – there has been this ‘Faster-than-light neutrino anomaly’ discovery, recently – this particular neutrino travels faster than the speed of light – BUT analysis are still taking place – we can’t hands or down say anything about it.

Also, is that even in our syllabus?

No, only for curiosity.. Thks for the help.

 

[ashfaaq7]

Can anyone tell me what is interference in Physics?

 

[ktc]

^ No problem

And Interference occurs when two light waves either adds up (join together) to increase the intensity of brightness. Or the two light waves collide and subtract one another – making it dim (decreasing the intensity).

 

[multixamza01]

because hydrogen comes below than zinc in reactivity series,it can not displace it...

Hydrogen has two places in the reactivity series . One between aluminium and zinc according to displacement of metals and one between lead and copper , according to preferential discharge . According to this knowledge both answer C AND D are correct. So Hydrogen can displace zinc.

 

[scouserlfc]

Hydrogen has two places in the reactivity series . One between aluminium and zinc according to displacement of metals and one between lead and copper , according to preferential discharge . According to this knowledge both answer C AND D are correct. So Hydrogen can displace zinc.

Nopes, the place u are talking abt between Al and Zn thats for Carbon which is just written there for understanding H original and correct position is above Cu !
Remember how Fe is reduced by carbon and not by hydrogen
Still confused look at a detailed Reactivity series on GOOGLE !

 

[snowbrood]

AOA...i am new to xtreme papers forums...i gave o levels exams last year...will try to answer ur questions whole heartedly...i appreciate ur efforts...keep it up

can anyone tell me why the smoke goes up in the sky from the chimney in dry day while the smoke goes goes down in wet day.... my friend told me that dry air is heavier than wet air harder for me to believe but can anyone help

 

[ktc]

^where did you read that from? 0_o

Could you please provide a link/question/paragraph?

Cuz, as far as I know, smoke always rises up a chimney, whether the atmosphere is dry or not, or else what’s the point of a chimney in the first place?

Wet air contains moisture content in it (water molecules) and therefore it is denser and heavier than dry air (which does not contain water molecules) - It’s a universal fact.

 

[multixamza01]

Nopes, the place u are talking abt between Al and Zn thats for Carbon which is just written there for understanding H original and correct position is above Cu !
Remember how Fe is reduced by carbon and not by hydrogen
Still confused look at a detailed Reactivity series on GOOGLE !

Okay -i still don't get it- but I'll take your word for it.

 

[ashfaaq7]

^ No problem

thks for the help!

 

[Dashing Cancerian]

A question for physics
need quick answer
Q.A truck of mass 2500 kg moving along a straight, level road. The engine enables a forward force of 12000 N to act on the truck. There are also counter forces that total 3200 N acting against the truck. As the truck goes faster with the same forward force, its acceleration becomes less. Eventually, the truck travels at a constant speed. Explain why this happens.

 

[farahdar]

Re: Biology,Chemistry & Physics Help Available Here !

salam guys can somebody plz tell me wats the diff b/t follows:
1)Allele
2)Gene
3)DNA
4Chromosomes!
tnx for the help!

Allele: Different form of a gene..like..theres a gene for the eye colour..alleles are different forms of it..like green, blue, brown ect
Gene: A unit of heredity in living organisms. They hold the info to build up and maintain an organisms cells and pass on traits to an off spring. Generally the contain info about an organisms traits.
DNA: Its a nucleic acid containing the genetic instructions used in the development and functioning of an organism. the dna segments carrying this info are the genes.
Chromosomes: its an organized structure of dna and proteins in a cell.. its the structure which contains the dna.
Just remember this..Cells contain chromosomes..which contain dna..which contain genes..which have different forms such as alleles

 

[ashfaaq7]

A question for physics
need quick answer

Because of frictions...

 

[farahdar]

oh thats what i wanted to make sureee .. thanks
what about if a plant were placed in a test tube containing hydrogen carbonate??
plant will release oxygyen isn't it .. so is oxygen also acidic??
what if plant + small animals such as snails were placed in the same tube?

all non metals make acidic oxides such as co2..so oxygen probably is too!

 

[Most_UniQue]

A question for physics
need quick answer
Q.A truck of mass 2500 kg moving along a straight, level road. The engine enables a forward force of 12000 N to act on the truck. There are also counter forces that total 3200 N acting against the truck. As the truck goes faster with the same forward force, its acceleration becomes less. Eventually, the truck travels at a constant speed. Explain why this happens.

At the start of the journey , there is opposite air resistance and frictional force of 3200 N which causes the truck to move at an acceleration of 3.52 m/s^2 with a resultant force of 8800 N (12000-3200) in the forward direction. As it speeds up , the counter forces (Air resistance and Friction which reduces its acceleration) also increase at the same rate until the resultant force acting on the truck is zero and the then car moves at constant speed.

For example : At the start journey its acceleration was 3.52m/s^2 . After a time of 20 seconds the opposite force acting on the truck is 6000 N so by using F=ma formula ( where F= 12000-6000=6000N , m=2500) acceleration will be 2.4 m/s^2 and this shows that its acceleration has been reduced . And later on when resultant force = 0 , acceleration would be zero and the truck will move at constant speed.

I hope you get it though Im not sure if its right or not

 

[Dashing Cancerian]

welll?????????? i wanted some explanation...