Chemistry 3/4 2013 Thread

[hardworker]

Thanks Haters gonna hate

Can someone please help me with this question-A concrete leaner contains concentrated HCl. A  25.00ml of volume of the cleaner was diluted to 250.00ml in a volumetric flask. A 20.00 ml of aliquot of 0.4480 M Na2CO3 solution was placed in a conical flask. Methyl Orange was used as an indicator the colour changed from yellow to pink when 19.84 ml of cleaner was added. 


Determine the ammount in mol of HCl present in the average titre? (Where do you get the average titre from).

Thanks in advance

0
hardworker: Great questionn! 19.84 mL? But i dont think you need it to answer the question( since you are asking for the moles , not the concentration)   , because you will find the moles by doing mole ratios with the Na2CO3


mcfluerry: great question! Shall try to answer it later !

 




But theres another part to the question which asks you to determine the ammount in mol of HCl in the volumetric flask? This is where im really confused do i use the 250 ml?

[Daenerys Targaryen]

1. Write the equation

2.
3.

As the HCl comes from the burette, that is the titre

[hardworker]

1. Write the equation

2.
3.

As the HCl comes from the burette, that is the titre

so i would use the tire i acquire from here to determine the HCl presenet in mol cause i got to here so the 0.01792 is the average tirte.

[AwayBroadcast]

Okay, so, first chem SAC. Brick cleaner one
Standard solution was made using 2.65g of Na2CO3, creating 250ml of a 0.1M solution
20.00mL aliquots of this solution were placed into conical flasks
Titrated with this was diluted solution of brick cleaner, made with 12.53g (10.00ml) of brick cleaner, plus enough water to fill the 250ml volumetric flask to the line.
I got an average titre of 17.02 (average was found from 4 results: 17.01, 17.05, 17.00 and 17.03)

My question is, how on earth do I find the percentage by mass of HCl in the brick cleaner?? I have been trying to get it for about an hour and it just will not work for me. Am I missing something?

Thank you!

[Daenerys Targaryen]

get the mol of HCL, times it by its Molar Mass. get the weight of it
then divide it by the mass of the brick cleaner orginally (original sample) and times by 100

[Edward21]

Just a more general 3/4 chemistry statement, with so many questions and resource books for VCE chemistry, does anyone else find it a bit overwhelming how many things there are out there for chemistry in 2013, it's hard to know where even to start    what are the best places to get questions that are similar to ones we would see on an exam that aren't past paper, and questions that are so difficult I may have to ask them here right on this very board !

[thushan]

Just a more general 3/4 chemistry statement, with so many questions and resource books for VCE chemistry, does anyone else find it a bit overwhelming how many things there are out there for chemistry in 2013, it's hard to know where even to start    what are the best places to get questions that are similar to ones we would see on an exam that aren't past paper, and questions that are so difficult I may have to ask them here right on this very board !

AN Chem book. Yes. I'm tooting my own horn.

[Conic]

AN Chem book. Yes. I'm tooting my own horn.

This. The book is amazing. I learned more about gravimetric and volumetric analysis from the detailed solutions than I did from the Heinemann textbook.

[Edward21]

AN Chem book. Yes. I'm tooting my own horn.

Haha yes I did order that one, and it is mighty fine. Are there any others like this, a large question book like checkpoints, but isn't checkpoints haha for chemistry?

[Limista]

One litre of an aqueous solution of potassium hydroxide (KOH) has a pH of 12.0 at 25 degrees celsius. The amount of pure HCl gas, in mol, that must be added to the solution to lower the pH from pH 12.0 to 2.0 would be?

Please help & thanks in advance 

[s.ay]

Okay so I'm struggling with the concept of back titrations. I understand how they occur, I just suck at the calculations Does anyone have a clear outline of the steps that need to be undertaken?
Thanks!

[thushan]

Okay so I'm struggling with the concept of back titrations. I understand how they occur, I just suck at the calculations Does anyone have a clear outline of the steps that need to be undertaken?
Thanks!

If the process were this:

To find the amount of Y -

React Y with a known amount of X (which is in excess) --> titrate excess X with Z

then work out:

n(X)added - the amount of X added
n(X)excess - the amount of X in excess; work this out by determining the amount of Z required to react with X, then work out the amount of X

Then you know n(X)reactwithY = n(X)added - n(X)excess

Then use that to determine n(Y) and so on.

[s.ay]

Ah, that makes sense! Now just to be able to put it into practice haha...
How would I go about using the above to work out this practice problem?

A 0.6000 g sample of K2CO3 (138.2055 g/mol) is dissolved in enough water to make 200.0 mL of solution A. A 20.00 mL aliquot of solution A is taken and put into an Erlenmeyer flask. To the flask is added 20.00 mL of 0.1700 M HCl:
K2CO3(aq) + 2HCl(aq) 2KCl(aq) + H2O(l) + CO2(g) The resulting solution is then titrated with 0.1048 M NaOH. NaOH(aq) + HCl(aq) H2O(l) + NaCl(aq)
How many mL of NaOH are used?

Thankyou!

[hardworker]

Can someone please explain to me how on a titration curve do you identify the end point and equivalence point preferably with a diagram please.

[LOLs99]

Hey , how do u determine the Mr(paracetamol) from the structure?
there is a diagram on the ques but I can't post it due to too large size.