Chemistry HL/SL help

[energetic]

hey!

quick question

how do i convert from mol/L TO mg/L?

[i2]=n/v = (2.875*10^(-6)/2)/0.2 = 0.0071875 mol/L

i want to convert 0.0071875 to mg/L

Thanks for a quich reply:)

[Sammie Backman]

hey!

quick question

how do i convert from mol/L TO mg/L?

[i2]=n/v = (2.875*10^(-6)/2)/0.2 = 0.0071875 mol/L

i want to convert 0.0071875 to mg/L

Thanks for a quich reply:)

Well, mass = amount of substance*molar mass, so you just multiply by the molar mass to get g/L.

Multiply this by 1000 and you have it in mg/L.

Edited September 19, 2011 by Sammie Backman

[HiddenDreamer]

For class, we have to calculate the seperate ΔH values for 3 equations. According to Hess' Law, ΔH1 + ΔH2 = ΔH3.

Reaction 1: NaOH(s) --> Na+(aq) + OH-(aq)

Mass of NaOH: 2g ; Volume of water= 100g

ΔT= 7 celcius

Reaction2: Na+(aq) + OH-(aq) + H+(aq) + Cl-(aq) --> Na+(aq) + Cl-(aq) + H2O(l)

Volume of 1.00M of NaOH: 50mL ; Volume of 1.00 M of HCl: 50mL

ΔT= 7.5 celcius

Reaction 3: NaOH (s) + H+(aq) + Cl-(aq) --> Na+(aq) + Cl-(aq) + H2O (l)

Mass of NaOH: 2g ; VOlume of 0.5M of HCl: 100mL

ΔT= 8 celcius

I did the mcΔT calculations using the combined mass (e.g. NaOH's mass + volume of water) however, ΔH1 + ΔH2 did not equal ΔH3. Are you supposed to only use the mass of NaOH? Because I tried that as well, and the values still didn't add up properly? What did I do wrong? What can I do to fix it?

Thanks in advance

I am doing the same lab it's actually rxn 1 + 3 = rxn 2.

[christran]

Is it possible for me to make a 7 on my IA even if there are mistakes and errors in the way I've collected data? My teacher told me that errors are fine as long as I write extensively about them in my evaluation, but I don't believe that entirely. I have the opportunity to redo my experiment but I'd rather not because it's so time consuming. I wouldn't object to it though if it would mean my grade could be better.

Edited September 29, 2011 by christran

[dessskris]

Is it possible for me to make a 7 on my IA even if there are mistakes and errors in the way I've collected data? My teacher told me that errors are fine as long as I write extensively about them in my evaluation, but I don't believe that entirely. I have the opportunity to redo my experiment but I'd rather not because it's so time consuming. I wouldn't object to it though if it would mean my grade could be better.

yes, can. if you evaluate your mistakes and suggest improvements in a really really sophisticated way, you could probably get cpp to ccc (c=complete, p=partial) in CE.

however your manupulation skills and technical skills might not be complete, then. I forgot how many marks come from these criteria but you're not likely to get full marks if you always make mistakes in your experiment.

I'd say repeat the experiment. it's your choice though.

[Drake Glau]

Is it possible for me to make a 7 on my IA even if there are mistakes and errors in the way I've collected data? My teacher told me that errors are fine as long as I write extensively about them in my evaluation, but I don't believe that entirely. I have the opportunity to redo my experiment but I'd rather not because it's so time consuming. I wouldn't object to it though if it would mean my grade could be better.

yes, can. if you evaluate your mistakes and suggest improvements in a really really sophisticated way, you could probably get cpp to ccc (c=complete, p=partial) in CE.

however your manupulation skills and technical skills might not be complete, then. I forgot how many marks come from these criteria but you're not likely to get full marks if you always make mistakes in your experiment.

I'd say repeat the experiment. it's your choice though.

Only 6 of the total 48 in the ppw come from manipulation skills. Don't think error would cause manipulation skill points to drop either. The way it was explained to me they were all about the ethics and safety of lab work not necessarily how well you could measure in a graduated cylinder. But I think everyone got 6/6 unless they simply sat around for their group4 project...

[kiwi.at.heart]

Can anyone explain the action of a acid-base indicator. My teacher never taught it to us and I'm struggling to understand it.

[Keel]

Can anyone explain the action of a acid-base indicator. My teacher never taught it to us and I'm struggling to understand it.

Most indicators are weak acids.

HIn <--> H⁺ + In^-

If HIn is colour A and In^- is colour B you can see that if there is an increase in [H⁺] the backward reaction will be favoured and the solution will change from colour B to colour A. If OH^- ions were added this would decrease [H⁺] and the forward reaction would be favoured causing an opposite colour change

[jonathan810]

Can anyone clarify more about electron configurations (SPDF)? (More specifically, when do you ever use 4dⁿ)

Edited October 13, 2011 by jonathan810

[Peanut Butter Jelly]

Can anyone clarify more about electron configurations (SPDF)? (More specifically, when do you ever use 4dⁿ)

transition elements

[kiwi.at.heart]

Can anyone clarify more about electron configurations (SPDF)? (More specifically, when do you ever use 4dⁿ)

Basically, you have you main energy levels, and then you have your sub-shell levels, which can be denoted by the spdf system.

When figuring out electron configurations you just follow three rules:

Aufbau Principle: electrons fill orbitals of lowest energy first

Hund’s Rule: unoccupied orbitals fill first, before putting the second e in the orbital

Pauli Exclusion Principle: no more than 2e can occupy an orbital and they must have opposite spin

The lowest energy orbital is 1s, then 2s, 2p, 3s, 3p, 4s, 3d, etc. 4s come first because it provides more stability than 3d which have a relatively similar energy levels. I haven't honestly seen any questions where you need to know past 3d but if you look at some configurations of higher atoms if will make sense.

As to your 4d question, once you get to the second row of transition metals 4d is in the configuration, but as above, I've never seen a question asking about the configuration of anything higher than Zn.

[jonathan810]

Thanks for the help!

although on some questions, when they ask you to state the full configuration of a d-block element, when do you include 4s² and when do you omit it (please correct me if I'm wrong, but I remember seeing some questions where 4s² is omitted and others where it's included?)

[Drake Glau]

D orbitals tend to be empty, half full (5), or completely full (10). When the configuration lands on a Nd3 spot the Ns2 electrons like to jump in there and make it Nd5. Same thing if it lands on Nd8, the 2 s electrons will fill in. I don't remember what happens when you hit something like Nd6 or Nd7 but my guess is that the "extra" electrons go to the p level in order to make the d half full.

So the s2 aren't really "omitted" but instead have just moved orbitals to make d happy for w/e reason it needs to be happy.

[jonathan810]

Thanks for the explanation!

Although another problem as risen.....

Which species does NOT contain de-localized electrons?

A:CH₃CH₂O^-

B:CH₃CO₂^-

C:O₃

D:NO₃^-

can someone please explain their reasoning (and also give a decent definition of 'delocalized electrons?)

Thanks

Edited October 14, 2011 by jonathan810

[dessskris]

Which species does NOT contain de-localized electrons?

A:CH₃CH₂O^-

B:CH₃CO₂^-

C:O₃

D:NO₃^-

can someone please explain their reasoning (and also give a decent definition of 'delocalized electrons?)

Thanks

delocalised electrons means the electrons are spread out throughout the molecule, so it's not concentrated (localised) at a point.

Gosh, my exams are in a few days and I forgot this thing. if I remember correctly, alkyl groups donate electrons and so in option A, it intensifies the negative density at O, hence the electrons are localised.

for option B, I think since there are two Oxygen atoms the negative charge although intensified by the presence of methyl group is spread between the two O atoms hence it's delocalised.

for option C, well three same atoms, the lone pair electrons are delocalised.

for option D, hmmm I'm not very sure but I think the charge should be quite spread out since there's no electron releasing or electron withdrawing particles.

[Peanut Butter Jelly]

The above question is basically asking which does not have resonance struction. Its either A or B but im too lazy to draw the lewis structures. If I were to guess, i would guess A

[dessskris]

orly? I guess it's HL stuff then? sorry, I was speaking with my knowledge from Further Organic Option! it's the only chapter in which I learnt delocalised electrons in such detail.

[Keel]

Thanks for the explanation!

Although another problem as risen.....

Which species does NOT contain de-localized electrons?

A:CH₃CH₂O^-

B:CH₃CO₂^-

C:O₃

D:NO₃^-

can someone please explain their reasoning (and also give a decent definition of 'delocalized electrons?)

Thanks

The definition of 'delocalised electrons' is 'electrons which are not assosiated with an atom or a particular covalent bond' i.e. the electron is free to move and is not restricted by a bond which is localised.

The correct answer to the question is A.

CH₃CH₂O^- is simply an ionised alcohol (ethanol) with a hydrogen missing. The electron MUST be localised because it is part of the oxygen atom.

If you answer the question through process of elimination you will find that B has delocalised electrons between the two C-O bonds, C has delocalised electrons between the two O-O bonds, and D has delocalised electrons between all 3 N-O bonds.

[Phillip7000]

Hello I am a IB student who failed to aquire a IB diploma on my 2011 march exam..

I have achived all good grades except HL Chemistry.

I am willing to only just pass the Chemistry HL.

I know that lab reports are something like 24% of finall grade and I need at least 3 as passing grade (which is combination of lab reports grade and exam final grades).

Sooo,what if i get (4, or 5 or 6) on my Lab reports, what exams grade I need to get in order to pass? (pls do the math for me)

[kiwi.at.heart]

Hello I am a IB student who failed to aquire a IB diploma on my 2011 march exam..

I have achived all good grades except HL Chemistry.

I am willing to only just pass the Chemistry HL.

I know that lab reports are something like 24% of finall grade and I need at least 3 as passing grade (which is combination of lab reports grade and exam final grades).

Sooo,what if i get (4, or 5 or 6) on my Lab reports, what exams grade I need to get in order to pass? (pls do the math for me)

Generally the overall percentage need for a 3 is about 35% for HL which is seriously easily. I am assuming you dont need to study any other subjects so just try and understand half of the syllabus and answer as much as you can on the exams and i can nearly guarantee you can get at least a 3 overall, as long as you put some effort in. Dont worry about exactly how much you just need to get a 3, because you always get more wrong on exams than you expect and you are just shooting yourself in the foot if you do.