Biology; Chemistry; Physics: Post your doubts here!

[SeraphicXynex]

Someone pleaase help!
http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_s08_qp_1.pdf
Question 30, the answer is B, but how is it possible? Could you give an explanation?

 

[***amd***]

What are the similarities between nervous system and hormonal system?
Before the start of a race why glucagon is not released but adrenaline is? :/

_both affect the whole body
_both are controlled by central nervous system
_both are present only in animals.

Glucagon is meant to increase the glucose level in the blood, and the need to ncrease it will be there if muscles work hard using and oxidising the glucose already present in the blood. Adrenalline is pruduced in the states of fear, anxiety and excitement (biologically: when metabolism is to be increased) its purpose is to dialate pupil and focus clearly and increase heartbeat.
Simply, before the race the player will bet excited and will try focus all the things, this will cause the Adrinalline to be produced first because the factor to trigger the production of Glucagon (muscle movement) will occur afterwards.

Hope you understand, but if you dont ask me again I will make it more precised and easy In Shaa Allah

 

[princess Anu]

I did! thanks =)

 

[ZohaKhan]

Mole ..stoichiometry..it is making me sick
as i read..i understand evrything n it seems easy but wen it comes to solving.. i always get stuck

HELP!

 

[ZohaKhan]

Mole ..stoichiometry..it is making me sick
as i read..i understand evrything n it seems easy but wen it comes to solving.. i always get stuck

HELP!

 

[***amd***]

Mole ..stoichiometry..it is making me sick
as i read..i understand evrything n it seems easy but wen it comes to solving.. i always get stuck

HELP!

write down alll the formulae on a saperate ppr and start reading them daily with a specific routine... and try to solve at least 1 Q a day... that really works

 

[princess Anu]

What are the by products of Anaerobic respiration in human : Lactic Acid and CO2 or only lactic acid???

 

[Ayyan :D]

What are the by products of Anaerobic respiration in human : Lactic Acid and CO2 or only lactic acid???

Lactic Acid, Carbon Dioxide and Energy.

 

[princess Anu]

Please help me solve this:
Barium sulfate, BaSO4, is made by the following reaction:
Ba(NO3)2(aq) + Na2SO4(aq) à BaSO4(s) + 2NaNO3(aq)
An experiment was begun with 75.00g of Ba(NO3)2 and an excess of Na2SO4. After collecting and drying the product, 63.45g BaSO4 was obtained. Calculate the theoretical yield and percent yield of BaSO4.

 

[Ram97]

Please help me solve this:
Barium sulfate, BaSO4, is made by the following reaction:
Ba(NO3)2(aq) + Na2SO4(aq) à BaSO4(s) + 2NaNO3(aq)
An experiment was begun with 75.00g of Ba(NO3)2 and an excess of Na2SO4. After collecting and drying the product, 63.45g BaSO4 was obtained. Calculate the theoretical yield and percent yield of BaSO4.

First take out the theoretical yield

Ba(NO3)2 : BaSO4

261 : 233
75 : x

x= 75/261 x 233
x= 66.95 g

Percentage Yield = Experimental Value/Theoretical Value x 100%
=63.45/66.95 x 100
=94.8%

Hope it helped

 

[princess Anu]

It did^ thanks!
Btw,
When does concentration thing matter in deciding who goes to anode and cathode in electrolysis!
Does it always matter?

 

[Ram97]

It did^ thanks!
Btw,
When does concentration thing matter in deciding who goes to anode and cathode in electrolysis!
Does it always matter?

The preferential discharge thingy????

 

[princess Anu]

Yes + concentration of ion

 

[Ram97]

If the solution is : NaCl (aq)
Here the ions are Na+, H+, Cl-, OH-
Preferential Discharge H+ and OH- ions released as there is a difference of more than 3 ions

If the solution is : conc.NaCl
Here the ions are Na+, Cl-, H+, OH-
Cl- ions released as thy are in cocnentration
H+ ions released as they accept electrons more readily than Na+ ions

 

[princess Anu]

In the second example you cited, Why na+ dont migrate even though they are concentrated?

 

[Ayyan :D]

In the second example you cited, Why na+ dont migrate even though they are concentrated?

In Aqueous solutions, H+ ions always migrate to the cathode. No other metal ion will be deposited on the Cathode, that's a rule.
You don't need to know the reason for this, which is not in the syllabus.

As far as the Anions are concerned, if the solution is dilute, then OH- will be deposited on Anode. If it is concentrated, then Cl, or other anion. Simple!

 

[princess Anu]

Okay! And is it necessary for the migrating anion to always be the one concentrated? In concentrated solutions

 

[Ayyan :D]

Okay! And is it necessary for the migrating anion to always be the one concentrated? In concentrated solutions

All ions migrate.
Cations migrate to the cathode.
Anions migrate to Anode.

It's the deposition which counts.
Don't mix MIGRATING And DEPOSITION.
OH- and Cl- both migrate to ANODE.
But CHLORIDE ION gets deposited if the solution is concentrated.


And yes, the anions should be concentrated.
The ANION is always concentrated in Concentrated solutions.
If they mention ''Dilute''.. then you have to deposit the OH- Ion.
But if they say CONCENTRATED or they don't mention anything, than you have to assume it's concentrated.

 

[princess Anu]

Allright, thankyou.

 

[Ayyan :D]

Allright, thankyou.

You're welcome.