Biology; Chemistry; Physics: Post your doubts here!

[XPFMember]

Thanks for caring so much about my time and how I utilize it.

Watever due. Was just suggesting , but if you wanna show attitude , then your choice.

Assalamoalaikum wr wb!

@ktc: May Allah reward you for your effort! Jazakillahu khairen!!

 

[nightmaressana]

guys, im really having trouble with the last bio chapter, the heredity one.... im having trouble in codominance and also in making crosses. can someone please help me with it?

 

[snowbrood]

http://www.xtremepapers.com/communi...pers-marking-schemes.11543/page-5#post-155927

though i dont study biology but i like ur effort keep up the spirit

 

[snowbrood]

The general principle of electrolysis of aqueous solutions is the ions lower in the cation/anion series get discharged first.

Then again, when it comes to concentrated aqueous solutions;

The CATION (positive ion/metal ion) lower in the reactivity series of metals gets discharged first - We do not take into account its concentration within the solution.

The ANION (negative ion/non mental ion) concentrated in the solution gets discharged first – here, we do not take into account its position within the anion series.

For example;
Concentrated aqueous Sodium Chloride, the ions present in the solution will be;

Na+ (Sodium ion)

Cl- (Chloride ion)

H+ (Hydrogen ion)

OH- (hydroxide ion)

We can see that Na+ and H+ are;

· Cations/positive ions/metal ions

· Na+ is concentrated in the solution

· H+ is diluted in the solution

· Na + is higher in the reactivity series

· H+ is lower in the reactivity series

So, which cation gets discharged first at the cathode? Na+ or H+?

It’s H+, despite the fact that it is NOT concentrated in the solution.

Why?

Cuz you should remember;

1. Cations/Metal ions undergo reduction at the cathode – it gains electrons and become atoms.

2. Metals have a tendency to lose electrons.

Now the Cation reactivity series is based on the electro positivity of each metal. Sodium metal being higher in the series has a higher tendency to lose electrons than Hydrogen, being lower in the series.

Going back to point 1, consequently, how do you expect Sodium to gain even more electrons when what it really wants is to lose it?
Hydrogen, on the other hand, being the good lil ion it is, is less electro positive (it has a lower tendency to gain electrons) and therefore, referring to point 1 again, the Hydrogen ion gets discharged first at the cathode, gains electrons and becomes hydrogen gas.

Moving on to the anions present in the solution;

In a concentrated solution, it is ALWAYS the ANION more concentrated in the solution gets discharged first at the anode, and undergoes oxidation (loses electrons) to become an atom/molecule. The position of the anion is not taken into consideration – it doesn’t matter if it’s higher or lower in the anion series.

So here, which anion gets discharged first at the anode? OH- or Cl-?

Cl-

Why?

Cuz Cl – is CONCENTRATED in the solution. OH- is not.

And they all lived happily ever after.

from where have u studied that good brother... can u suggest me the book that u use please

 

[multixamza01]

guys, im really having trouble with the last bio chapter, the heredity one.... im having trouble in codominance and also in making crosses. can someone please help me with it?

Do you know terminology? Like what is homozygous, heterozygous, phenotype , genotype , dominant allele and recessive allele? I think its these that you dont under stand and so are having trouble with crosses and concept of co- dominance. So please tell me if you do. Because if someone explains and you dont know , then it would seem like Arabic to you.

 

[ktc]

from where have u studied that good brother... can u suggest me the book that u use please

JazakAllah Kheiren! From lots of sources

There’s a book is called ‘IGCSE Chemistry’ - B Earl and L D R Wilford.

Then there’s also, “GCSE Chemistry” – Longman.

But the key is to practice as much as past paper questions as you can! Studying and reading through books isn’t only gonna help – practice until you’ve got the concept fixed in your mind and make sure it doesn’t leave - Which can further be done by more practice!

Btw, it’s 'sister’

 

[snowbrood]

JazakAllah Kheiren! From lots of sources

There’s a book is called ‘IGCSE Chemistry’ - B Earl and L D R Wilford.

Then there’s also, “GCSE Chemistry” – Longman.

But the key is to practice as much as past paper questions as you can! Studying and reading through books isn’t only gonna help – practice until you’ve got the concept fixed in your mind and make sure it doesn’t leave - Which can further be done by more practice!

Btw, it’s 'sister’

sorry for that sister u really helped May Allah grant u heaven

 

[ktc]

sorry for that sister u really helped May Allah grant u heaven

May Allah Grant all of us Heaven! Ameen!

 

[XPFMember]

May Allah Grant all of us Heaven! Ameen!

aameen

 

[Alchemist4lyf]

The general principle of electrolysis of aqueous solutions is the ions lower in the cation/anion series get discharged first.

Then again, when it comes to concentrated aqueous solutions;

The CATION (positive ion/metal ion) lower in the reactivity series of metals gets discharged first - We do not take into account its concentration within the solution.

The ANION (negative ion/non mental ion) concentrated in the solution gets discharged first – here, we do not take into account its position within the anion series.

For example;
Concentrated aqueous Sodium Chloride, the ions present in the solution will be;

Na+ (Sodium ion)

Cl- (Chloride ion)

H+ (Hydrogen ion)

OH- (hydroxide ion)

We can see that Na+ and H+ are;

· Cations/positive ions/metal ions

· Na+ is concentrated in the solution

· H+ is diluted in the solution

· Na + is higher in the reactivity series

· H+ is lower in the reactivity series

So, which cation gets discharged first at the cathode? Na+ or H+?

It’s H+, despite the fact that it is NOT concentrated in the solution.

Why?

Cuz you should remember;

1. Cations/Metal ions undergo reduction at the cathode – it gains electrons and become atoms.

2. Metals have a tendency to lose electrons.

Now the Cation reactivity series is based on the electro positivity of each metal. Sodium metal being higher in the series has a higher tendency to lose electrons than Hydrogen, being lower in the series.

Going back to point 1, consequently, how do you expect Sodium to gain even more electrons when what it really wants is to lose it?
Hydrogen, on the other hand, being the good lil ion it is, is less electro positive (it has a lower tendency to gain electrons) and therefore, referring to point 1 again, the Hydrogen ion gets discharged first at the cathode, gains electrons and becomes hydrogen gas.

Moving on to the anions present in the solution;

In a concentrated solution, it is ALWAYS the ANION more concentrated in the solution gets discharged first at the anode, and undergoes oxidation (loses electrons) to become an atom/molecule. The position of the anion is not taken into consideration – it doesn’t matter if it’s higher or lower in the anion series.

So here, which anion gets discharged first at the anode? OH- or Cl-?

Cl-

Why?

Cuz Cl – is CONCENTRATED in the solution. OH- is not.

And they all lived happily ever after.

Thanks man. For that indepth reply. Thing is, I asked my chemistry teacher as well. He says, that Cations ARE discharged if in higher concentration, but this is never asked in O' Levels. All they ask is for anions, particularly, Chlorine. The Cations which are discharged due to higher concentrations, are the moderately reactive ones, such as Zinc, Iron, Lead, Hydrogen, Copper. The ones above, are highly electropositive (as you pointed out), and the ones below, are too unreactive. Hope this helps someone out

 

[Alchemist4lyf]

Sorry. Small mistake.
1. Cations which get discharged due to high concentration are Zinc, Iron, Lead.
2. Hydrogen, Copper, Silver, Gold will get discharged anyway, due to preferrential discharge.
3. The ions above Zinc, such as Aluminium and stuff, are too electropositive, as Ktc mentioned. So they won't get discharged in high conc.

Anyways, like I said, my teacher told me they don't usually ask this stuff.

 

[nightmaressana]

y

Do you know terminology? Like what is homozygous, heterozygous, phenotype , genotype , dominant allele and recessive allele? I think its these that you dont under stand and so are having trouble with crosses and concept of co- dominance. So please tell me if you do. Because if someone explains and you dont know , then it would seem like Arabic to you.

es, i get a little confused with the terminologies, but im working on it. but, i would really like if you did explain it to me!

 

[multixamza01]

y
es, i get a little confused with the terminologies, but im working on it. but, i would really like if you did explain it to me!

Phenotype : How someone looks. Their physical appearance , the features that distinguished one from another. e.g a plant maybe tall or short. rabbits are brown or white. These all are ''phenotypes''.

Genotype : The internal distinguishing features. How the genes of one organism differ from another. Get this straight. Phenotypes distinguish organisms , but genotypes are responsible for bring out that distinction.

Allele : One of a pair of genes . e.g B , b.

Homozygous condition : Condition in which both alleles are the same. eg BB , bb.
Heterozygous condition : Condition in which alleles differ . eg like Bb.

Dominant allele : The allele that is - lets say just for the sake of concept - more powerful. It will always express itself if present. We denote it as a capital letter . therefore B is the dominant allele. Now lets say B is the allele for tallness , so a plant with a genotype of BB ( homozygous condition) will be tall . Also a plant with heterozygous condition ( Bb) will also be tall. As the dominant allele supresses the recessive( weak ) allele.

Recessive allele : the allele that is weak . it only expresses itself if the dominant allele is absent. therefore a plant will only be short if it has a genotype of bb.

Now i suggest you give crosses another try. the basic problem in the chapter is solved. You shouldn't have problems , but if you still do then feel free to ask. Try to practise as many crosses as possible . find them from the Internet.

 

[scouserlfc]

Well the solution must be aqueous!

Are u sure bro because even in aqueos solutions Cu will discharge as it is lower than Hydrogen in the reactivity series as long as i remember their is no way to produce hydrogen at cathode in the electrolysis of CuSO4 solutions.(FROM O LEVEL point of view ) !

 

[ashfaaq7]

Which of these travels faster? Light or Neutrino?

 

[ktc]

Which of these travels faster? Light or Neutrino?

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 down say anything about it.

Also, is that even in our syllabus?

 

[SalmanPakRocks]

Are u sure bro because even in aqueos solutions Cu will discharge as it is lower than Hydrogen in the reactivity series as long as i remember their is no way to produce hydrogen at cathode in the electrolysis of CuSO4 solutions.(FROM O LEVEL point of view ) !

Oh yeah! I forgot about Cu! Thanks for the guide.

 

[snowbrood]

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

 

[snowbrood]

can anyone solve the q.1

 

[memyself15]

well when you heat at the bottom of the tube, the air in the tube will get heated and rise up the tube by convection. the hot air will cause ice to melt. when you heat at the top, the air which gets heated will rise and flow out of the tube. so heat don't reach the ice by convection. ice will melt due to heat which travels by conduction through the glass tube(which is itself a poor conductor).
please correct me if i am wrong.