Chemistry: Post your doubts here!

[Ericyong]

A: (91.1*28 + 7.9*29+30)/100 = 28.009
B: (92.2*28 + 4.7*29 + 3.1*30)/100 = 28.109

So, B.

The idea is to multiply the relative abundance with the isotopic mass and take the average of the abundances.

Do note, though, that sometimes the three or four or however many abundance percentages are given DO NOT add up to 100%. You've to be careful what you divide with!

I know how to do it if i were to calculate the answers one by one, but i was actually looking for an alternative way to find it without doing that.

But i guess it's impossible since there's 3 unknown and 1 equation.

Thanks btw!

 

[AbbbbY]

I know how to do it if i were to calculate the answers one by one, but i was actually looking for an alternative way to find it without doing that.

But i guess it's impossible since there's 3 unknown and 1 equation.

Thanks btw!

What you're asking for is only possible when there are 2 isotopes. This question was merely testing your concept of finding the average atomic mass via the percentage abundance approach.

 

[UVYEAH]

I need help with the following question:
9701_w12_qp_23.pdf
Q5

The molecular formula C4H8O can represent a number of compounds which have different
functional groups and which show different types of isomerism.
Compounds H, J and K each have the molecular formula C4H8O.
In each of the molecules of H, J and K,
● the carbon chain is unbranched and the molecule is not cyclic,
● no oxygen atom is attached to any carbon atom which is involved in π bonding.
When compound H is reacted with sodium metal, a colourless fl ammable gas is produced.
Both J and K give an orange-red precipitate when reacted with 2,4-dinitrophenylhydrazine
reagent but only K reacts with Fehling’s solution.

Clearly, J and K are carbonyl groups. But that would indicate a C=O double bond exists, and that violates the condition they give us: "no oxygen atom is attached to any carbon atom which is involved in π bonding." because the C=O bond involves one π bond.
What am I doing/thinking wrong here?

 

[Nigarm]

Please help me! I have a problem solving these 2 questions :
1. Calculate the mass of water produced in the reaction between 0.1 L of hydrogen gas and
20 g of copper oxide (II).
2. What volume (in normal conditions) is occupied by a gas produced in the reaction
between 30 g of ethylene and the excess of hydrogen gas?

 

[Zepudee]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s11_qp_42.pdf

Q3 (C) can someone explain?

 

[Zepudee]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w11_qp_43.pdf
Q3(e) (iv) why is [CH3CO2Na] = 0.05 and [CH3CO2H]= 0.075 ?

 

[prajwol khatri]

Somebody pl suggest me that will i have to mug up the ph ranges for different indicators or not... And will i have to remember the end points of them???

you better remember it... other wide no choice you have to mug up...it

 

[♣♠ Magnanimous ♣♠]

I need help with the following question:
9701_w12_qp_23.pdf
Q5

The molecular formula C4H8O can represent a number of compounds which have different
functional groups and which show different types of isomerism.
Compounds H, J and K each have the molecular formula C4H8O.
In each of the molecules of H, J and K,
● the carbon chain is unbranched and the molecule is not cyclic,
● no oxygen atom is attached to any carbon atom which is involved in π bonding.
When compound H is reacted with sodium metal, a colourless fl ammable gas is produced.
Both J and K give an orange-red precipitate when reacted with 2,4-dinitrophenylhydrazine
reagent but only K reacts with Fehling’s solution.

Clearly, J and K are carbonyl groups. But that would indicate a C=O double bond exists, and that violates the condition they give us: "no oxygen atom is attached to any carbon atom which is involved in π bonding." because the C=O bond involves one π bond.
What am I doing/thinking wrong here?

Can you give paper link and ques no plzz

 

[princess Anu]

Somebody please explain me this statement, ''Ammonia is more likely to deviate from ideal gas behaviour as it possesses a dipole due to the the lone pair of electrons above nitrogen. As a consequence, hydrogen bonds form between the slightly positive hydrogens and slightly negative nitrogens, increasing the boiling point of ammonia. These intermolecular forces result in deviations from ideal gas behaviour''
what is a dipole? how do they result in Hydrogen bond? how do they cause deviations from ideal gas behaviour?

 

[Zinedine Sanzaied]

https://www.xtremepapers.com/commun...hysics-chemistry-biology-and-computing.35102/
Hey guys, I've uploaded some notes in this thread. It covers the organic part of the A2 Chemistry syllabus. You may find them useful. The thread also contains notes for Physics, Biology and Computing.

 

[Eric Hadriel Wong]

Q26, which reducing agent is used?

 

[emma914]

someone help me how to handle the NMR questions....totally blank

 

[Thought blocker]

someone help me how to handle the NMR questions....totally blank

NMR means? :/

 

[emma914]

NMR means? :/

nuclear magnetic resonance

 

[emma914]

nuclear magnetic resonance

NMR comes under applications of analytical chemistry

 

[scouserlfc]

Somebody please explain me this statement, ''Ammonia is more likely to deviate from ideal gas behaviour as it possesses a dipole due to the the lone pair of electrons above nitrogen. As a consequence, hydrogen bonds form between the slightly positive hydrogens and slightly negative nitrogens, increasing the boiling point of ammonia. These intermolecular forces result in deviations from ideal gas behaviour''
what is a dipole? how do they result in Hydrogen bond? how do they cause deviations from ideal gas behaviour?

dipole is basically a slight positive and negative charge forming on a substance hence it getting polar. Substances which are polar and have an H atom attached to either F,O and N elements can have hydrogen bonding between the molecules like NH3 can Hydrogen bond with another NH3 and etc.
Ideal gas behavior constitutes on many points and the most important two that are only obeyed by ideal gases and not real gases (like CH4,CO2 and etc) are that ideal gases have no intermolecular forces between them and that volume of the gas molecule is neglegible to the volume of the whole gas . But since NH3 has Hydrogen bonds which are the strongest bonds the two conditions dont get satisfied and u have deviation from ideal behaviour which gives PV against P graph not a straight line as expected but kind of a parabola . While H2 is a bit different it has Van der waals forces which are very weak as u know and these forces being weak allow H2 to behave as an ideal gas when extremes of temp and low pressures are applied and those two conditions get satisfied and H2 becomes an ideal gas for that temperature.
If u are still not happy do get your problem solved

 

[princess Anu]

how does hydrogen bonding violates the second condition i.e. volume of the gas molecules is negligible compared to the volume of the gas?
why is PV against P graph a straight line for ideal gas?
Is it that only high temperatures and low pressures make a gas ideal always or is it the case with hydrogen only?


Thanks A lot.

 

[Eyunice]

H e l p p l s

Really Urgent!

 

[manutd96]

hydrogen sulphide reacts with water according to the following equation. H2S(aq)+ 2H2o(aq) --> <--- (reversible) 2H3o+(aq) + S2- (aq)

Which of the following aqueous solutions when added would cause the system at equilibrium to shift to the left?

A. NH4Cl
B. Na2CO3
C. CH3COONa
D. NH3

Pls teach me this question thx !

 

[Charlotte20102013]

Hi, is it true to say : Addition polymers have monomers that are alkenes, and condensation polymers have monomers that are not alkenes, but that have two functional groups per molecule.?
Like if I was given a monomer, and asked if it will form addition or condensation polymers, if I see an alkene functional group ( double bond ) can I straight away conclude that it will give addition polymers?