Chemistry: Post your doubts here!

[hamzashariq]

Which pair of elements have bonds of the same type between their atoms in the solid state?
A aluminium and phosphorus
B chlorine and argon
C magnesium and silicon
D sulphur and chlorine

explain please

 

[Kim Shaw]

Which pair of elements have bonds of the same type between their atoms in the solid state?
A aluminium and phosphorus
B chlorine and argon
C magnesium and silicon
D sulphur and chlorine

explain please

The question was already asked before on this thread...#1401. I'll write what smzimran wrote:

Not A because Aluminium has metallic bonding while Phosphorus has a simple molecular struture with covalent bonds and Van der Waals forces
Not B because chlorine is diatomic (covalent bonding) while argon is a noble gas : monoatomic
Not C because Mg has metallic bonding while Silicon has covalent bonds
It is D because both have molecular structure with covalent bonds

 

[aaaamfa]

the diagram for glyceryl trieleostearate is given...plz write the full question WITH diagrams next time...
http://2.bp.blogspot.com/-BvWESUAvwHw/Tea_fPjiS0I/AAAAAAAAAKE/DBmBo9gYuGM/s1600/glyceryl trieleostearate.jpg
Step 1: Count the hydrogen atoms in the side-chains.
Upper side-chain and lower side-chain: 2 x (3+6+6+14) = 58
Middle side-chain: 3 + 6 + 6 + 14 = 29
Step 2: Count the hydrogen atoms in each residue
First residue: 3 + 8 + 6 + 14 = 31
Second residue x 2 (because two side-chains are converted): 2 x (3 + 14 + 2 + 14) = 66
Step 3: Calculate how many hydrogen atoms had to be added to each side-chain in order to form the residues.
Upper and lower side-chain residues have 66 - 58 extra hydrogens = 8 extra hydrogens
Middle side-chain residue has 31-29 extra hydrogens = 2 extra hydrogens
Step 4: You know that 10 hydrogen atoms have been added to the original molecule. Each hydrogen molecule contains two hydrogen atoms, so there are 10/2 = 5 hydrogen molecules ie. 5 moles of hydrogen

srry i will take care of it nxt time but one more explaination what is side chain and middle chain etc

 

[aaaamfa]

9. answer is B because nitric acid is HNO3. It dissociates in water to give 1H+ ion and 1 NO3- ion. It is the only one which dissociates to give 1 mole H+, like HCl(which dissociates to give 1 H+ and 1 Cl-)

10. answer is D. This is found in Equilibria chapter. You have to know le Chatelier’s principle to do that. Basically, on RHS of equa, there is OH-. By making solution more alkaline, u are adding more OH-. The system will thus shift to LHS so as to oppose this change. Thus LHS will be favoured and mor V2+ will be formed.

11. answer is D. This is again an Equilibria question. If u study the graph given, u will see that, as pressure is increased and temperature is decreased, %yield of Z increases. To understand the pressure part, in equation there r more moles on LHS so increasing pressure will increase Z as RHS will be favoured. Equilibrium constant is a CONSTANT(as its name suggests)... so it does NOT change. Now, coming back to graph, if by decreasing temperature %yield of Z is increasing, this means that forward reaction is favoured by low temp, so forward is exothermic(this is understood better if u have knowledge on Chatelier’s principle).

33. ans is C. Catalyst merely lowers activation energy. So it increases BOTH forward and backward reaction. Kinetic energy is the SAME, with or without enzyme. As far as i know, kinetic energy rises ONLY when temp rises, u have to confirm that with some1 else..but i’m 100& sure that catalyst does NOT in ANY WAY increase kinetic energy. So, only statement 2 and 3 are correct...hence C is correct ans.

If anything is unclear, just msg me and I’ll clarify it if i can

ur explaination is very easy and the best to understand once u have explained i dont think so there is a room for any confusion

 

[Kim Shaw]

srry i will take care of it nxt time but one more explaination what is side chain and middle chain etc

Sidechains are basically what 'hang off ' the main body(a bit like the main trunk of the tree and its branches). if the diagram given in question is taken as an example, the upper side chain is CH3(CH2)3CH=...=CH(CH2)7(the first side chain from the top). middle side chain is one after the upper one and so on. The main body is the CO2CH2-CO2CH-CO2CH2 bit of the molecule.
Btw thnx for the compliment! ^-^

 

[SilverCrest]

Aoa
Does any one knowvwhy do we assume that the concentration of solid remains constant in an equilibrium ?

 

[princess Anu]

Covalent compounds don't contain ions, then how do acids, who are covalent compounds, produce H+ ions in aqueous solutions?

 

[daredevil]

Aoa
Does any one knowvwhy do we assume that the concentration of solid remains constant in an equilibrium ?

rate of forward and backward reaction becomes equal at equilibrium. the amount of solid broken down (for example) is equal to the amount of solid being formed on the other way. this is why we assume that the net affect is zero.

 

[SilverCrest]

rate of forward and backward reaction becomes equal at equilibrium. the amount of solid broken down (for example) is equal to the amount of solid being formed on the other way. this is why we assume that the net affect is zero.

i dont get it
what of there is no solid being formed at the other end.for example the equilibrium?Wont the concentration of solid remain constant in Kc
H2O (g)+ C(s) ----> CO(g) + H2(g)

there is only one solid here .
is it because the total volume and total mass of solid are changing in such a way that the concentration of the solid remains constant?

 

[daredevil]

i dont get it
what of there is no solid being formed at the other end.for example the equilibrium?Wont the concentration of solid remain constant in Kc
H2O (g)+ C(s) ----> CO(g) + H2(g)

there is only one solid here .
is it because the total volume and total mass of solid are changing in such a way that the concentration of the solid remains constant?

its not a matter of there being a solid on both sides.
Look at this for example:
A(s) <---> B(aq) + C(aq)

the above shows an equation of a reversible reaction with A,B and C being any chemical substance.
as reversible reactions take place there is reaction going on in both directions. at the start if we have A(s) and it has to decompose into B and C [this is only an example, the reaction may or may not be decomposition. it doesnt matter] the reaction is more inclined and fast towards the RHS - which means that the net effect of the reaction is towards RHS even if B and C have started the backward reaction slowly and to some extent. this is due to the high concentration of A at the start of the experiment.
the reaction proceeds to counter the effect of high concentration as you know..

now as the reaction proceeds, concentration of B and C increases gradually. as the concentration of B and C increases the speed of reaction in the backwards reaction also increases. so that relatively more and more B and C combine to form A just as A is breaking down to make B and C.
A point comes when the speeds of forward and backward reactions becomes equal. This is equilibrium! Now the amount of A made is same as the amount of B and C formed [relatively as per molar requirements and stuff - DETAILS ]

anyways....
now even when A is breaking down, it is also being formed at the same rate. Net effect is zero. thus the amount of solid remains constant.

I hope this answers your question. Do ask if you have ANY other querries about this or anything else. GOOD LUCK! =)

 

[SilverCrest]

the

its not a matter of there being a solid on both sides.
Look at this for example:
A(s) <---> B(aq) + C(aq)

the above shows an equation of a reversible reaction with A,B and C being any chemical substance.
as reversible reactions take place there is reaction going on in both directions. at the start if we have A(s) and it has to decompose into B and C [this is only an example, the reaction may or may not be decomposition. it doesnt matter] the reaction is more inclined and fast towards the RHS - which means that the net effect of the reaction is towards RHS even if B and C have started the backward reaction slowly and to some extent. this is due to the high concentration of A at the start of the experiment.
the reaction proceeds to counter the effect of high concentration as you know..

now as the reaction proceeds, concentration of B and C increases gradually. as the concentration of B and C increases the speed of reaction in the backwards reaction also increases. so that relatively more and more B and C combine to form A just as A is breaking down to make B and C.
A point comes when the speeds of forward and backward reactions becomes equal. This is equilibrium! Now the amount of A made is same as the amount of B and C formed [relatively as per molar requirements and stuff - DETAILS ]

anyways....
now even when A is breaking down, it is also being formed at the same rate. Net effect is zero. thus the amount of solid remains constant.

I hope this answers your question. Do ask if you have ANY other querries about this or anything else. GOOD LUCK! =)

thanks for the detailed reply! but..
then shouldnt the concentrations of B and C also be constant?
could you also tell me how to solve this question?do we include residual volume of oxygen?

 

[daredevil]

the

thanks for the detailed reply! but..
then shouldnt the concentrations of B and C also be constant?
could you also tell me how to solve this question?do we include residual volume of oxygen?


View attachment 33586

they are reacting with O2 so it is a combusiton reaction.
make equations of combustion reaction for every compound separately. calculate the volume of oxygen used up for each reaction using molar ratio. molar ratio is the same as volume ratio for gas due to a constant molar gas volume.

subtract the amount of O2 used for each from the total volume and u will get the RESIDUAL gas.
then see which results match for the residual.

and no problem

 

[Kim Shaw]

Covalent compounds don't contain ions, then how do acids, who are covalent compounds, produce H+ ions in aqueous solutions?

Firstly, acids produce hydrozonium ions(H3O+) not H+ ions. Let's take HCl as an example of an acid.
HCl is strictly speaking - a polar covalent molecule with a partial positive charge on hydrogen and a partial negative charge on chlorine(due to different electronegativities). When this is dissolved in water, water too being a polar molecule with a partial positive charge on hydrogen and a partial negative charge on oxygen, hydrogens of HCl are surrounded by oxygens of water forming dipole dipole bonds. So also the chlorines are surrounded by hydrogens of water. When the dipole-dipole bonds are formed, the original bond between H and Cl weakens and ultimately breaks leading to ionization.

 

[crys123]

how to study chemistry of life chapter no 28 of chemistry a2 i just dont get it

chemistry of life is completely from AS biology. im guessing u didnt take biology. i'd suggest taking help from a classmate/friend of yours. Get somebody who took biology in AS level to explain you the chapter. Or you could try watching videos from youtube. I dont know if there is any available on this topic. But I can assure you it is a really easy chapter! Its just basic stuff.

 

[crys123]

The answer is C.

 

[daredevil]

chemistry of life is completely from AS biology. im guessing u didnt take biology. i'd suggest taking help from a classmate/friend of yours. Get somebody who took biology in AS level to explain you the chapter. Or you could try watching videos from youtube. I dont know if there is any available on this topic. But I can assure you it is a really easy chapter! Its just basic stuff.

isn't it from the applications booklet?? @snowbrood

 

[snowbrood]

isn't it from the applications booklet?? @snowbrood

yea it is in application booklet i am not a bio student for girls bio is easy but for me bio gets over my head

 

[snowbrood]

chemistry of life is completely from AS biology. im guessing u didnt take biology. i'd suggest taking help from a classmate/friend of yours. Get somebody who took biology in AS level to explain you the chapter. Or you could try watching videos from youtube. I dont know if there is any available on this topic. But I can assure you it is a really easy chapter! Its just basic stuff.

lol i am studying from 10 days yet i cant even understand two pages cytoplasm ribosomes and so much maybe because i dont know about these stuff. actually i don't get anything without intuition and intuition in chemistry of life for a student that dont study bio is difficult to get

 

[snowbrood]

isn't it from the applications booklet?? @snowbrood

hey help me tell me what how to study this chapter

 

[daredevil]

yea it is in application booklet i am not a bio student for girls bio is easy but for me bio gets over my head

heyy easy there -_- u r talking to a GIRL who cant stand BIO even having been studying it for 5 years straight :/
yh well i get it where u're standing actually ..... but i haven't done applications yet so i'm afraid i cant help u all that much. my only advice would be to consult more sources on this particular topic. see if there are any relevant lectures on Khanacademy.com and search the webb life like said before. maybe you'll get a hang of it. and i am guessing that if this is a very basic chap then it must be o levels biology stuff so just imagine that u r studying it for the first time in o levels and have to learn it or something? Good Luck... maybe in a few months wen i have done it then i can be of more help. if later on you need help with any specific concepts of this stuff then tell me /... i'll try my best to help u out =)