HSC Chemistry Question Thread

[lalall]

Hi Lalall!,

1. I'm inclined to say that correct rinsing of glassware improves accuracy, as this would help you get a result closer to the actual value. But at the same time, validity is also a measure of how well your variables are controlled, the variable being the pH of the solutions. I think it impacts both.
2. Some of the other things impacting validity are :
          -Volume of unknown solution
          -Type of indicator used
          -Concentration of standard solution
          -Equipment used
          -Use of a control, that is, the aliquot with indicator untitrated.
3.  Reliability is determined through repetition of titration and then the evaluation of the concordance of results across the three titres. By repeating it multiple times, outliers can be to identified and excluded.

Makes perfect sense! Thank you

[lalall]

Someone can correct me but I feel like it would, which is concerning.

Which sources are telling you bromothymol blue and which are telling you phenolphthalein?

Most of the sources online use phenolphthalein, however when we did it in class our teacher said that we should use bromothymol blue because the equivalance point is around 7 . What you said earlier makes sense as well.

[RuiAce]

Most of the sources online use phenolphthalein, however when we did it in class our teacher said that we should use bromothymol blue because the equivalance point is around 7 . What you said earlier makes sense as well.

It's really hard to say, because I'm not sure if the equivalence point actually is around 7 at all for this one. I wouldn't be surprised if it were, but there's definitely evidence to deter that thought

[preliminary17hsc18]

Couple questions on identifying ions...
- When trying to identify an anion or cation if there's only ONE present in the solution, do we just conduct each test with a new sample or do we still have to filter everything?
- When there are multiple anions or cations present, do we have to filter at EVERY step?
Thanks in advance

[cocopops201]

Hi!

How do I explain the conversion of chemical energy to electrical energy in a dry cell?
Do I just include the anode, cathode and overall equation on how certain chemicals react with each other generating a 1.5 Voltage of the battery?

Thank you to anyone who responds.

[KT Nyunt]

Couple questions on identifying ions...
- When trying to identify an anion or cation if there's only ONE present in the solution, do we just conduct each test with a new sample or do we still have to filter everything?
- When there are multiple anions or cations present, do we have to filter at EVERY step?
Thanks in advance

Hello 
1) Filtering is more for separating mixed solutions and for gravimetric analysis. So for identifying which ion is present in a solution where only one ion is present, this wouldn't call for any filtering. Although, I believe you would have to use a new sample for each test, especially if a precipitate is formed in a test. Technically, if no precipitate is formed in a test, you can add another solution into that same test and see if a precipitate forms (but if you're testing for cations, your anions would always have to be soluble - e.g. nitrates - and vice versa for anions). But to keep things simple and clear on what solutions are placed in a test, use a new sample for each test.

2) Yes, now we filter. Maybe not at every step (e.g. to test the presence of carbonate ions in a mixture: you would add acid like HCl. If gas bubbles form then you can confirm carbonate ions were present in the solution and this also removes the carbonate ions from the solution, thus this doesn't call for filtering) but you would definitely filter whenever you've formed a precipitate.

Hi!

How do I explain the conversion of chemical energy to electrical energy in a dry cell?
Do I just include the anode, cathode and overall equation on how certain chemicals react with each other generating a 1.5 Voltage of the battery?

Thank you to anyone who responds.

Hi! I think just including the anode and cathode half questions and the 1.5V is fine (I don't think you even need the overall equation). This should be sufficient in explaining the chemistry behind the dry cell. The transfer of electrons in the redox reaction between the anode and cathode produces 1.5 V.


Hope this helps! 

[clovvy]

If anyone can explain how the titration curve really works I will appreciate greatly.. I have been looking through textbooks and notes but I still don't get how the graphs work and I have never been able to do HSC and regular questions on them T_T.. I like equivalence points and stuff I find very confusing

[varun.amin]

Hi!

How do I explain the conversion of chemical energy to electrical energy in a dry cell?
Do I just include the anode, cathode and overall equation on how certain chemicals react with each other generating a 1.5 Voltage of the battery?

Thank you to anyone who responds.

Hi cocopops201,

This is just a rough guide on explaining the conversion process:

I'd first give a basic outline of what the cell consists of (the anode, the cathode, the electrolyte). Then I'd go on to explain each step with a relevant chemical equation. Start at the anode and give the anodic half equation, explaining how the zinc atoms of the anode donate their electrons to form Zn2+ ions. Then as the dry cell is connected to a device/circuit, the excess electrons from the anode flow through the circuit, travelling to the carbon rod. This movement of electrons is what forms the electrical current which powers the device. After progressing through the entire circuit, the electrons enter the carbon rod cathode. This is where they combine with manganese dioxide and water. This reacts to produce manganese (III) hydroxide. Then I'd give the cathode half equation.

Hope this helps

[varun.amin]

If anyone can explain how the titration curve really works I will appreciate greatly.. I have been looking through textbooks and notes but I still don't get how the graphs work and I have never been able to do HSC and regular questions on them T_T.. I like equivalence points and stuff I find very confusing

Hi Clovvy,

Basically, a titration curve is the plot of the pH of the solution you're testing versus the volume of the titrant added as the titration progresses.   When you carry out a simple acid-base titration, you use an indicator to tell you when you have the acid and alkali mixed in exactly the right proportions to "neutralise" each other.

Simply put, the equivalence point, is the exact point in a titration when moles of one titrant equal the moles of the substance being titrated. It is theoretical point.

The end point, is the point at which an indicator changes color. It’s actual point not theoretical which you can determine it in lab.

I found this link helpful in understanding the concept, hopefully it helps

https://www.khanacademy.org/test-prep/mcat/chemical-processes/titrations-and-solubility-equilibria/a/acid-base-titration-curves

[cocopops201]

Hello 

I was just wondering, what have been the affects of the haber process' chemistry on society and the environment? It's for a 6 marker question that says to include 'TWO examples you have studies, analyse the impact of applications of chem on society & environment'. Where I'll be doing radioisotopes for the other example.

THANKS

[KT Nyunt]

Hello 

I was just wondering, what have been the affects of the haber process' chemistry on society and the environment? It's for a 6 marker question that says to include 'TWO examples you have studies, analyse the impact of applications of chem on society & environment'. Where I'll be doing radioisotopes for the other example.

THANKS

Hi,
Here are some things I'd include about the Haber process:
Applications of the Haber Process include: cleaning products, producing nylon and dyes etc. But the most impactful contributions would have to be the production of fertilisers and explosives.

The Haber Process [ N2(g) + 3H2(g) <--> 2NH3(g) ] {as they ask for the chemistry, definitely make sure you include the equations} allowed for ammonia to be industrially produced. This process was developed by Fritz Haber at the time of the 1st world war, where countries involved were on the brink of starvation and his country, Germany, was losing the war. Ammonia is required for plant growth. By developing the Haber process, ammonia could be industrially produced and used in fertilisers, immensely increasing crop growth and diminishing world hunger. Today, the use of fertiliser is still very prevalent in increasing crop growth. Furthermore, the Haber process could also be used to create explosives. (side note: Fritzy was a bit of a mad fella. Look it up - he practically caused the deaths of masses of Jews in WWII holocaust - Hitler who?) The production of explosives for Germany led to the prolonging of WWI.

Thus, the Haber Process greatly impacted the environment and society as it increased crop growth, diminishing world hunger, however it's use in making explosives also prolonged the 1st world war.

There's definitely more you could say about the Haber process and the history behind it but this should help you get started

Hope this helps

[cocopops201]

There's definitely more you could say about the Haber process and the history behind it but this should help you get started

Hi, thanks so much for helping!
I was also wondering how I could incorporate the Haber process' impact on todays overpopulation due to its contribution of fertilizers for food production?

Thanks 

[KT Nyunt]

Hi, thanks so much for helping!
I was also wondering how I could incorporate the Haber process' impact on todays overpopulation due to its contribution of fertilizers for food production?

Thanks 

Yeah I guess you could argue that! As it is used to produce ammonia for fertilisers, it increased crop growth, solving world hunger, thus feeding the world, hence increasing populations 

[fallenorigins]

Hi,
I just had a couple of questions regarding testing for ions

1. When there are more than one ion in the sample, should you always follow the flowchart process or can you test each individually (or is that only for one ion in the sample)?
2. Do you only filter the solution when there is a precipitate formed, or even when there is no prepcipitate if there are more than one ion in the sample?

Thanks! 

[RuiAce]

Hi,
I just had a couple of questions regarding testing for ions

1. When there are more than one ion in the sample, should you always follow the flowchart process or can you test each individually (or is that only for one ion in the sample)?
2. Do you only filter the solution when there is a precipitate formed, or even when there is no prepcipitate if there are more than one ion in the sample?

Thanks! 

1. A flow chart is designed so that it's very explicit what to do first, if you need to do multiple tests at once. The flow chart itself should be able to guide you which to do first, without impacting on everything else.

2. Only when there's precipitation, because if no precipitate (i.e. no solid) forms, there's nothing to filter out. Filtration exists to split a solid-liquid mixture.