HSC Chemistry Question Thread

[anotherworld2b]

Oh ok i was confused because i was looking at how the periodic table was arranged by increasing atomic weight( which is the atomic number?)

I was also wondering if someone could explain the factor of shielding by inner electrons in periodic trends.

I also wanted to confirm whether a atom's nuclear charge is the same as core charge as a factor of periodic trends? Could it be defined as the atteaction between the nucleus and the outer electron shell?

I was also wondering in questions where you have explain elemental spectra, emission spectroscopy, atomic absorption spectroscopy and mass spectroscopy are there key points that should be explained? In my answers i generally write too little and lose marks 

[RuiAce]

Oh ok i was confused because i was looking at how the periodic table was arranged by increasing atomic weight( which is the atomic number?)

I was also wondering if someone could explain the factor of shielding by inner electrons in periodic trends.

I also wanted to confirm whether a atom's nuclear charge is the same as core charge as a factor of periodic trends? Could it be defined as the atteaction between the nucleus and the outer electron shell?

I was also wondering in questions where you have explain elemental spectra, emission spectroscopy, atomic absorption spectroscopy and mass spectroscopy are there key points that should be explained? In my answers i generally write too little and lose marks 

These concepts are not in the HSC course.

Also no, atomic weight (aka atomic mass) is the decimal number associated with it. The atomic number is just the number of protons there are.

[QC]

Oh ok i was confused because i was looking at how the periodic table was arranged by increasing atomic weight( which is the atomic number?)

I was also wondering if someone could explain the factor of shielding by inner electrons in periodic trends.

I also wanted to confirm whether a atom's nuclear charge is the same as core charge as a factor of periodic trends? Could it be defined as the atteaction between the nucleus and the outer electron shell?

I was also wondering in questions where you have explain elemental spectra, emission spectroscopy, atomic absorption spectroscopy and mass spectroscopy are there key points that should be explained? In my answers i generally write too little and lose marks 

Hey, just to add to what Rui said, I'm pretty sure that before Henry Mosley, the table was arranged by mass number (the average number of protons and neutrons that are known in all isotopes of that element. E.g hydrogen is 1.008, almost all isotopes of hydrogen exist as just 1 proton and one electron however, some isotopes such as deuterium and tritium which are 1 proton and 1 neutron and 1 proton and 2 neutrons respectively exist but in much lower quantities than the 1 proton no neutrons hydrogen isotope. Also, the atomic number is the number of protons which is unique to each element e.g hydrogen 1, helium 2, lithium 3 etc.
Also I think that mass spectroscopy is a way of measuring ionisation/radiation so that could be useful for that dotpoint.
Finally, you don't need to know about core charge (the nuclear charge experienced by an outershell electron) but it is the same as the atom's nuclear charge I think. 

[Shadowxo]

Oh ok i was confused because i was looking at how the periodic table was arranged by increasing atomic weight( which is the atomic number?)

I was also wondering if someone could explain the factor of shielding by inner electrons in periodic trends.

I also wanted to confirm whether a atom's nuclear charge is the same as core charge as a factor of periodic trends? Could it be defined as the atteaction between the nucleus and the outer electron shell?

I was also wondering in questions where you have explain elemental spectra, emission spectroscopy, atomic absorption spectroscopy and mass spectroscopy are there key points that should be explained? In my answers i generally write too little and lose marks 

Atomic number = number of protons in that elements (number of protons is what defines the element) eg Oxygen, 8
Atomic weight = average weight of that element (protons and neutrons), eg Oxygen, 16.0

Bit rusty on this as I don't think it's assessed in VCE but
Shielding: electrons in their shells are attracted to the nucleus as they are negative and the nucleus is positive due to the protons. For the valence shells, they experience the attraction of the nucleus AND the repulsion from the other negative electrons in the non-valence shells closer to the nucleus, so the more electron shells -> more shielding. So as you go down the periodic table, more shells therefore more shielding, and number of inner shells stays the same from left to right so same shielding across.

If I remember correctly, nuclear charge = charge from protons (number of protons), core charge = charge from protons - charge from inner electrons (protons - inner shell electrons). So nuclear charge is the same as atomic number (increases both down and across periodic table), core charge increases across the periodic table and remains the same down the periodic table. Core charge takes into account the shielding effect from the inner shell electrons and is the attraction between the nucleus and outer electron shell, and nuclear charge is just the charge of the protons.

You should include what elements/molecules they can be used on, how they differentiate them if applicable (eg retention time) and what they measure (eg retention time, concentration). I would ask your teacher what you should include for them but these should be the main ones.

[RuiAce]

He's from WA so to be fair he doesn't know what gets taught here. Which is a terrible chemistry course.

But any input for him is always appreciated.

[beau77bro]

what is the best way to study for chemistry, generally but also, what is the best textbook or workbook to be using for questions. currently im using conquering as info source and also doing question but im also trying to do surfing. opinions? better way to study? i dont really have a teacher or non-snake classmates, so what should i be doing to maximise study both in actual study and in doing questions?

thankyouuuuu

[RuiAce]

what is the best way to study for chemistry, generally but also, what is the best textbook or workbook to be using for questions. currently im using conquering as info source and also doing question but im also trying to do surfing. opinions? better way to study? i dont really have a teacher or non-snake classmates, so what should i be doing to maximise study both in actual study and in doing questions?

thankyouuuuu

Textbook discussion. Surfing feels more like a summary-based textbook; more of an aid. Spending a bit of time on it isn't too bad, but I wouldn't go for a lot of them. At the end of the day, past papers all the way.

"Best way to study" - non-existent, because the most optimal strategy varies from person to person. As opposed to better ways. Note that study is a matter of you choosing to put your time into a subject, but in general has an objective - the EXAM. So a better approach would be to study in an appropriate manner - make all your notes ASAP, know them well, and then when you can do as many past papers as possible.

[beau77bro]

Textbook discussion. Surfing feels more like a summary-based textbook; more of an aid. Spending a bit of time on it isn't too bad, but I wouldn't go for a lot of them. At the end of the day, past papers all the way.

"Best way to study" - non-existent, because the most optimal strategy varies from person to person. As opposed to better ways. Note that study is a matter of you choosing to put your time into a subject, but in general has an objective - the EXAM. So a better approach would be to study in an appropriate manner - make all your notes ASAP, know them well, and then when you can do as many past papers as possible.

thankyou rui your my saviour hahaha im gonna start printing out and pumping out half yearly past papers asap, appreciate the advice and thankyou math god

[RuiAce]

thankyou rui your my saviour hahaha im gonna start printing out and pumping out half yearly past papers asap, appreciate the advice and thankyou math god

Good luck 

[bsdfjnlkasn]

Hey there,

Here are some notes I took down in class today, and I was wondering if someone could help me clarify the details of acid rain as I'm still a bit iffy about it all  - Questions are in bold

1.   Acidic oxides are released into the atmosphere
•   When the concentrations of these gases in the air reach high levels, acid rain can occur

2.   Acidic oxides dissolve in condensing water and as a result are transformed into an acid
•   Acids are then sometimes oxidised by ozone or O2 molecules
-   Become more acidic, having stronger effects
When acids are oxidised are hydrogen ions formed, is this what makes the falling rain more acidic (as in what is referred to 'stronger effects')?

•   Sulfur dioxide and nitrogen dioxide are soluble and so reduce the pH of rain water considerably
-   What has solubility got to do with reducing pH? Is it because the dioxides don't ionise and hence increase H+ concentrations?


Thank you! Any help would be greatly appreciated 

[QC]

Hey there,

Here are some notes I took down in class today, and I was wondering if someone could help me clarify the details of acid rain as I'm still a bit iffy about it all  - Questions are in bold

1.   Acidic oxides are released into the atmosphere
•   When the concentrations of these gases in the air reach high levels, acid rain can occur

2.   Acidic oxides dissolve in condensing water and as a result are transformed into an acid
•   Acids are then sometimes oxidised by ozone or O2 molecules
-   Become more acidic, having stronger effects
When acids are oxidised are hydrogen ions formed, is this what makes the falling rain more acidic (as in what is referred to 'stronger effects')?

•   Sulfur dioxide and nitrogen dioxide are soluble and so reduce the pH of rain water considerably
-   What has solubility got to do with reducing pH? Is it because the dioxides don't ionise and hence increase H+ concentrations?


Thank you! Any help would be greatly appreciated 

When acids are oxidised are hydrogen ions formed, is this what makes the falling rain more acidic (as in what is referred to 'stronger effects')?
So acid rain primarily is formed via the formation of sulfur and nitrogen oxides (N2O, NO2, SO2,SO3) In the presence of water, sulfur trioxide (SO3) is converted rapidly to sulfuric acid:
SO3 (g) + H2O (l) → H2SO4 (aq)
Nitrogen dioxide reacts with OH to form nitric acid:
NO2 + OH· → HNO3
So these are acids right so they therefore reduce the pH of the the water, (its like a dilute acid which has a low pH) And yes, as you said, hydrogen ions are formed as the HNO3 and H2SO4 dissociate to form H+ and NO3- ions and H+ and SO42- ions. And if you refer to the definition of pH (pH=-log[H+]). This therefore means that as the concentration of H+ ions increases, the strength of the acid increases. You then have to talk about the impacts of strong acid on the environment and human health etc.
What has solubility got to do with reducing pH? Is it because the dioxides don't ionise and hence increase H+ concentrations?
Think about it, if the oxide cannot dissolve, it cannot interact with the H2O and thus H+/H3O+ ions cannot be formed when they form their respective acids. To add to this, they are non-metal oxides so they are acidic and therefore also increase [H+]. I'm not sure what you mean by dioxides not ionising hence increase [H+]. The dioxides react with the H2O and then ionise as acids.

[RuiAce]

NO2 + OH· → HNO3

I like the response, but I want to pinpoint that this equation is wrong.

What actually happens is
2 NO₂ + H₂O -> HNO₂ + HNO₃

The equation provided should, I hope, be possible. But it's not what actually happens.

[QC]

I like the response, but I want to pinpoint that this equation is wrong.

What actually happens is
2 NO₂ + H₂O -> HNO₂ + HNO₃

The equation provided should, I hope, be possible. But it's not what actually happens.

Hey Rui, is there a marathon type thread on Atar Notes where rather than just answering questions, people ask exam style questions giving the amount of marks each question is worth and then others mark using a marking rubric. I think this is much more useful then even doing past papers since you actually get to know what your answer would be worth rather than the p bad sample answers/rubrics that are available.

[RuiAce]

Hey Rui, is there a marathon type thread on Atar Notes where rather than just answering questions, people ask exam style questions giving the amount of marks each question is worth and then others mark using a marking rubric. I think this is much more useful then even doing past papers since you actually get to know what your answer would be worth rather than the p bad sample answers/rubrics that are available.

Do you want one of these? I can try discussing it with some higher authorities.

[Aussie1Italia2]

Hello! Please and thank you for the help!

I have a titration calculation and I'm not entirely sure what I'm doing.

If it takes 50mL of 0.5M KOH to completely neutralise 125 mL of sulfuric acid solution (H₂SO₄), what is the concentration of the H₂SO₄ solution.