hardest chem questions (3 Viewers)

[RANK 1]

TOMS was replaced by OMI in 2000.
haha

whats your point? are u saying that just because TOMS got replaced its no longer considered an instrument to measure the ozone?

 

[RANK 1]

people did and you told them that it wasnt hard

because it wasnt, i highly doubt that a 7 marker on membrane filters is the hardest question u've seen

 

[Squishxmishyx]

What was the hardest past paper?!

 

[nichorowitz]

Now CaCO3 + 2HCl ---> CaCl2 + H2O + CO2

Therefore CaCO3:HCl
1:2
therefore twice as many moles of HCl are needed

Hence there are zero moles of HCl left over

??

 

[RANK 1]

The following diagram shows the steps taken in an experiment to find the percentage of pure calcium carbonate in a sample of limestone. The impurities in the limestone are solids that do not react with either the HCL or NaOH.
-Weigh out 10g of limestone
-Add 100mL of 2molL Hydrochloric acid to the limestoneor
-Allow all reaction to cease
-Titrate the reaction mixture against 1molL Sodium Hydroxide solution

1) Calculate the amount of HCl left after the reaction of the Calcium Carbonate with the acid
2) Calculate the amount of HCl that reacted with the Calcium Carbonate in the limestone
3) What is the percentage of pure Calcium Carbonate in the limestone?

Lol tit rate

1) 0.000179838 mols. 0 mols (1 s.f)

2) 0.1999820161 mols, 0.2 mols (1 s.f)

3) u sure they didnt give u the amount of NaOH it was being titrated against?

 

[Squishxmishyx]

The following diagram shows the steps taken in an experiment to find the percentage of pure calcium carbonate in a sample of limestone. The impurities in the limestone are solids that do not react with either the HCL or NaOH.
-Weigh out 10g of limestone
-Add 100mL of 2molL Hydrochloric acid to the limestoneor
-Allow all reaction to cease
-Titrate the reaction mixture against 1molL Sodium Hydroxide solution

1) Calculate the amount of HCl left after the reaction of the Calcium Carbonate with the acid
2) Calculate the amount of HCl that reacted with the Calcium Carbonate in the limestone
3) What is the percentage of pure Calcium Carbonate in the limestone?

Lol tit rate

Answer to the hardest Chemistry question.
1) 0.16
2) 0.04
3) 80%

 

[RANK 1]

how?

 

[RANK 1]

u sure u didnt leave out bits of the question there?

 

[Squishxmishyx]

how?

I don't even know.
Should I bother attempting it?
Is this a back titration question?

u sure u didnt leave out bits of the question there?

Woops

-Result 40mL of NaOH is needed to nautralise.

 

[RANK 1]

Woops

-Result 40mL of NaOH is needed to nautralise.

this why we got it wrong...

 

[RANK 1]

but yea then its not that hard, u just have to work backwards

 

[Trebla]

A student is trying to work out the formula of an unknown acid he was given. So far he knows that the formula takes the form H_nXO₃, where n is an unknown positive integer and X is an unknown non-metallic element which can either be Phosphorous (P), Sulfur (S), Carbon (C) or Nitrogen (N). To determine which of the four elements X actually is for the unknown acid, the student performs a series of titrations.

The student decides to prepare a secondary standard solution of NaOH by titrating it with a primary standard solution of 0.1064 mol/L of HCl.

The result was that 25.00mL of NaOH required 25.00mL of HCl with concentration 0.1064 mol/L for an end-point with the indicator colour change.

The student then dissolved 2.569 grams of H_nXO₃ in water to make a 250.0mL solution. He performed a titration with the unknown acid H_nXO₃ and the standard NaOH solution.

The result was that 25.00mL of the standard NaOH required 16.31mL of H_nXO₃ solution for an end-point with the indicator colour change.

Determine the identity of X and the value of n using the given choices. Justify your answer.

 

[RANK 1]

A student is trying to work out the formula of an unknown neutral acid he was given. So far he knows that the formula takes the form H_nXO₃, where n is an unknown positive integer and X is an unknown non-metallic element which can either be Phosphorous (P), Sulfur (S), Carbon (C) or Nitrogen (N). To determine which of the four elements X actually is for the unknown acid, the student performs a series of titrations.

The student decides to prepare a secondary standard solution of NaOH by titrating it with a primary standard solution of 0.1064 mol/L of HCl.

The result was that 25.00mL of NaOH required 25.00mL of HCl with concentration 0.1064 mol/L for an end-point with the indicator colour change.

The student then dissolved 2.569 grams of H_nXO₃ in water to make a 250.0mL solution. He performed a titration with the unknown acid H_nXO₃ and the standard NaOH solution.

The result was that 25.00mL of the standard NaOH required 16.31mL of H_nXO₃ solution for an end-point with the indicator colour change.

Determine the identity of X and the value of n using the given choices. Justify your answer.

firstly how do u have a neutral acid

 

[RANK 1]

A student is trying to work out the formula of an unknown neutral acid he was given. So far he knows that the formula takes the form H_nXO₃, where n is an unknown positive integer and X is an unknown non-metallic element which can either be Phosphorous (P), Sulfur (S), Carbon (C) or Nitrogen (N). To determine which of the four elements X actually is for the unknown acid, the student performs a series of titrations.

The student decides to prepare a secondary standard solution of NaOH by titrating it with a primary standard solution of 0.1064 mol/L of HCl.

The result was that 25.00mL of NaOH required 25.00mL of HCl with concentration 0.1064 mol/L for an end-point with the indicator colour change.

The student then dissolved 2.569 grams of H_nXO₃ in water to make a 250.0mL solution. He performed a titration with the unknown acid H_nXO₃ and the standard NaOH solution.

The result was that 25.00mL of the standard NaOH required 16.31mL of H_nXO₃ solution for an end-point with the indicator colour change.

Determine the identity of X and the value of n using the given choices. Justify your answer.

after a long calculation, Molar mass of H_nXO₃= 63.0081 g

M_HnX= 63.0081 - 48 = 15.0081g

therefore logically X cant be P or S which leaves N and C

but for it to be C the formula of the acid would be H2CO3 which molar mass = 62.026

therefore it has to be HNO3 which molar mass = approx 63

therefore n=1 and X=N

amirite?

 

[silence--]

^ i got the same :L

holy shit that is a monster of a question though. haha

guess the chance of that popping up in HSC is extremely low though

 

[RANK 1]

i want about 2 of these in there, they separate the good from average

 

[Trebla]

after a long calculation, Molar mass of H_nXO₃= 63.0081 g

M_HnX= 63.0081 - 48 = 15.0081g

therefore logically X cant be P or S which leaves N and C

but for it to be C the formula of the acid would be H2CO3 which molar mass = 62.026

therefore it has to be HNO3 which molar mass = approx 63

therefore n=1 and X=N

amirite?

Yep

How's that for something 'hard'? lol

 

[RANK 1]

Yep

How's that for something 'hard'? lol

it was a pretty solid question but doesnt cut the 'hard' range cos as long as u follow the basic algebra and procedures its doable

 

[silence--]

^ i suppose but i guarantee that most HSC candidates would probably not even attempt that.

HSC really isnt going to get much harder than that lol

 

[RANK 1]

which is why we need something to separate the elite from the rest