HSC Chemistry Question Thread

[DamnDhruv]

Hello Just wondering if anyone can answer this question of mine (they have not given me the specific heat capacity so I dobt know how to figure it out)

how much heat is required to raise the temperature of 68.0g of AlF3 from 25.0C

BTW I am new to the forum do please do tell if I did something wrong (posted on the wrong place or didnt ask the question properly.
thanks

[horse9996]

Hello Just wondering if anyone can answer this question of mine (they have not given me the specific heat capacity so I dobt know how to figure it out)

how much heat is required to raise the temperature of 68.0g of AlF3 from 25.0C

BTW I am new to the forum do please do tell if I did something wrong (posted on the wrong place or didnt ask the question properly.
thanks

Where did you get that question from?

[Dragomistress]

Hi,
I am confused about why for K, they did not divide by the concentration of NH4HS. Or am I just wrong?

Isn't for aA+bB-->cC+dD going to K=([C]^c*[D]^d)/([A]^a^b)?.

[dermite]

Hi,
I am confused about why for K, they did not divide by the concentration of NH4HS. Or am I just wrong?

Isn't for aA+bB-->cC+dD going to K=([C]^c*[D]^d)/([A]^a^b)?.

NH4HS is a solid; you dont consider solids in K calculations

[DamnDhruv]

Where did you get that question from?

my teacher gave it to me.

[horse9996]

my teacher gave it to me.

I'm not too sure, I think you need the specific heat capacity. Then you can solve for the change in heat (delta H) where delta T = 1

[SpanishPear]

Hello Just wondering if anyone can answer this question of mine (they have not given me the specific heat capacity so I dobt know how to figure it out)

Hey!
Welcome to the forums!
I must say, I've never experienced a question like this, I don't actually think this is in the HSC Chemistry syllabus!
Unless they give you the specific heat capacity and are testing your knowledge of the formula: delta H = -mCdeltaT.
Although, there could be a really niche application of this that I'm missing, so someone correct me if I'm wrong!
My reccomendation would be to email your teacher for solutions and share it with the forums!

[SpanishPear]

So basically an experiment can't be reliable unless its valid, therefore discussion on validity is relevant here?

I actually disagree with this.
Reliable is essentially is the experiment getting similar results result every time , akin to consistency.
Think about an a archery target. An experiment is:
Valid: If the aim was to hit the center of the target, and the center of the target was hit.
Reliable: If the arrow was shot several times, would it hit the same area?
Here's an infographic:
https://www.google.com.au/search?q=validity+vs+accuracy+chemistry&safe=strict&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiD-ey2j4reAhUHd94KHVYIBkIQ_AUIDigB&biw=1440&bih=821#imgrc=kGgM-_U6otnKcM:
In regards to your question, I would talk about how repeating and avereging values would increase reliability. BUT this only works if the experiment is conducted exactly the same each trial, hence you should talk about the steps taken and how you can make sure each step is done precisely (eg using exact measurements rather than "a few drops" )

Accuracy is how does the experimental value compare to the accepted value.


TLDR: An experiment CAN be reliable and invalid.

[DamnDhruv]

Hey!
Welcome to the forums!
I must say, I've never experienced a question like this, I don't actually think this is in the HSC Chemistry syllabus!
Unless they give you the specific heat capacity and are testing your knowledge of the formula: delta H = -mCdeltaT.
Although, there could be a really niche application of this that I'm missing, so someone correct me if I'm wrong!
My reccomendation would be to email your teacher for solutions and share it with the forums!

Got it thanks !!

[catkittenz]

process information from secondary sources to summarise the use of ethanol as an alternative car fuel, evaluating the success of currenT usage


im very confused with evaluating current usage


thankuu

[jazcstuart]

process information from secondary sources to summarise the use of ethanol as an alternative car fuel, evaluating the success of currenT usage


im very confused with evaluating current usage


thankuu

Hi, welcome to Atar Notes!!!

Essentially you need to evaluate how ethanol is being used as an alternative fuel, and how successfully. The main current use is for ethanol/petrol mixes, eg. E10 which is 10% ethanol. This has not been used overly successfully in Australia, due to misconceptions about the damage this can cause to car engines. However ethanol/petrol blends have been used more successfully in other countries, for example in Sweden 85% ethanol blends are common, and Brazil requires all cars to be able to accept at least 25% ethanol blends. Brazil and Argentina have 100% hydrous ethanol fuels (so 4% water), which is a very clean fuel, however existing car engines must be modified.

Therefore the evaluation would be that the use of has great potential to replace dwindling petroleum resources and reduce CO₂ emissions, however it is currently restricted to petrol blends with 5-25% ethanol. This is because existing car engines must be modified to accept higher proportions of ethanol, and more research is needed to make ethanol more cost effective and efficient as an alternative fuel.

Hope this helps 

[sofichu]

Hey Can anyone help me with this question

Explain the role of the conjugate acid/base pair, H2PO4 ^- / HPO4 ^ 2-, in maintaining the pH of living cells. Include chemical equations in your answer ( including one that represents equilibrium)

Thank you!!!!

[Jakeybaby]

Hey Can anyone help me with this question

Explain the role of the conjugate acid/base pair, H2PO4 ^- / HPO4 ^ 2-, in maintaining the pH of living cells. Include chemical equations in your answer ( including one that represents equilibrium)

Thank you!!!!

Hello!

The conjugate acid/base pairing of H₂PO₄^- and HPO₄^2- can neutralise both and acid or a base within a cell, meaning that this pairing acts as a buffer system within the cell. As it is able to neutralise an acid or a base within the cell, it can maintain the pH.

The following equation would be sufficient:
HPO₄^2- + H₃O⁺ <-> H₂PO₄^- + H₂O

I hope this helps!

[sofichu]

Hey again :’)
Stuck on another question this time. Any help would be appreciated !

Describe how you would prepare a H2PO4 ^- / HPO4 ^ 2- buffer solution with a pH of 7.40 from the sodium salts of both the H2PO4 ^ - and HPO4 ^ 2- ions .
Ka = 6.2 x 10^-8

[Jakeybaby]

Hey again :’)
Stuck on another question this time. Any help would be appreciated !

Describe how you would prepare a H2PO4 ^- / HPO4 ^ 2- buffer solution with a pH of 7.40 from the sodium salts of both the H2PO4 ^ - and HPO4 ^ 2- ions .
Ka = 6.2 x 10^-8

What are your thoughts so far?
I would be using the Henderson-Hasselbalch equation to solve this problem.