HSC 2012-2015 Chemistry Marathon (archive) (3 Viewers)

[Drsoccerball]

re: HSC Chemistry Marathon Archive

The key word is "industrial"

 

[Ekman]

re: HSC Chemistry Marathon Archive

It's a trial question.

But I need help for this question, the sample answer still doesn't make me understand why cell Y was chosen.

Well you should know that sodium hydroxide is produced via the electrolysis of concentrated brine. So Cell Y has the products of the electrolysis of concentrated brine, hence that is the answer.

 

[Mr_Kap]

re: HSC Chemistry Marathon Archive

How do you know what happens when: Acid + NH3 --> ??

It is not a standard acid base reaction as no H2O can form.

 

[leehuan]

re: HSC Chemistry Marathon Archive

HCl + NH3 -> NH4Cl
H2SO4 + 2NH3 -> (NH4)2SO4
HNO3 + NH3 -> NH4NO3

CH3COOH + NH3 <--> CH3COONH4

Basically speaking, you form an ammonium salt

(Note that from Brosnted-Lowry theory, since ammonia is a base, it can accept a proton)

 

[Mr_Kap]

re: HSC Chemistry Marathon Archive

HCl + NH3 -> NH4Cl
H2SO4 + 2NH3 -> (NH4)2SO4
HNO3 + NH3 -> NH4NO3

CH3COOH + NH3 <--> CH3COONH4

Basically speaking, you form an ammonium salt

(Note that from Brosnted-Lowry theory, since ammonia is a base, it can accept a proton)

How did you do the H2SO4 one? It confuses me because it is diprotic.
Shouldn't it just be: H₂SO₄ + NH₃ -> NH₅²⁺ + SO₄^2- -> NH₅SO₄

(i know its unbalnced but yeh)

 

[BlueGas]

re: HSC Chemistry Marathon Archive

For the industrial people, would love to know the answer for this.

Explain how the industrial method of producing soap differs from that used in school laboratories. (4 marks)

 

[someth1ng]

re: HSC Chemistry Marathon Archive

How did you do the H2SO4 one? It confuses me because it is diprotic.
Shouldn't it just be: H₂SO₄ + NH₃ -> NH₅²⁺ + SO₄^2- -> NH₅SO₄

(i know its unbalnced but yeh)

NH3 only has 1 lone pair so it can only accept 1 proton so you need 2 protons.

 

[BlueGas]

re: HSC Chemistry Marathon Archive

This is a method for the electrolysis of sodium chloride, but I wanna ask one question, what are some precautions of this experiment to minimise hazards, or to dispose of reactants and products safely?

 

[Mr_Kap]

re: HSC Chemistry Marathon Archive

This is a method for the electrolysis of sodium chloride, but I wanna ask one question, what are some precautions of this experiment to minimise hazards, or to dispose of reactants and products safely?

Idk - maybe perform in a fume hood to ensure that harmful chlorine gas is not breathed in.
Do not touch the electrodes as can cause electricution.

 

[BlueGas]

re: HSC Chemistry Marathon Archive

Another question, for those that do industrial chemistry, what's a micelle in terms of soap, grease, water, etc.

 

[sharoooooo]

re: HSC Chemistry Marathon Archive

Another question, for those that do industrial chemistry, what's a micelle in terms of soap, grease, water, etc.

basically a suspended blob of grease

 

[Ekman]

re: HSC Chemistry Marathon Archive

Another question, for those that do industrial chemistry, what's a micelle in terms of soap, grease, water, etc.

A micelle is a group of soap molecules that form into a spherical shape where the hydrophobic tails arrange themselves inside the sphere and the hydrophilic polar heads form the surface of the micelle sphere.

 

[BlueGas]

re: HSC Chemistry Marathon Archive

A micelle is a group of soap molecules that form into a spherical shape where the hydrophobic tails arrange themselves inside the sphere and the hydrophilic polar heads form the surface of the micelle sphere.

Ah, so micelles basically make up an emlusion?

 

[Ekman]

re: HSC Chemistry Marathon Archive

Ah, so micelles basically make up an emlusion?

Micelles can be formed without grease or dirt being in the centre of the molecule. This is because of the hydrophobic tail. When talking about micelle formation when cleaning grease or dirt, you would say: "The polar hydrophilic heads of the micelles decrease the surface tension between water and the grease molecule, allowing the formation of an water-grease emulsion as soap molecules are known as surfactants"

 

[BlueGas]

re: HSC Chemistry Marathon Archive

Quick question for the industrial chemistry peoples, after determining the equilibrium constant, how can the value be used to determine the position of the equilibrium?

 

[InteGrand]

re: HSC Chemistry Marathon Archive

Quick question for the industrial chemistry peoples, after determining the equilibrium constant, how can the value be used to determine the position of the equilibrium?

 

[BlueGas]

re: HSC Chemistry Marathon Archive

I've got this same information in my notes but I didn't understand it haha, since Q is the reaction quotient, what is the reaction quotient? That's what I didn't understand.

 

[InteGrand]

re: HSC Chemistry Marathon Archive

I've got this same information in my notes but I didn't understand it haha, since Q is the reaction quotient, what is the reaction quotient? That's what I didn't understand.

http://chemwiki.ucdavis.edu/Physica...Between_K_And_Q#Q_vs._K:_What_Does_It_Mean.3F

 

[Ekman]

re: HSC Chemistry Marathon Archive

Quick question for the industrial chemistry peoples, after determining the equilibrium constant, how can the value be used to determine the position of the equilibrium?

I dont think you need to go into reaction quotient because when the system is at equilibrium, it still can favour one side. From what ive been taught:

K <1 means the point of equilibrium is on the reactants side

K >1 means the point of equilibrium is on the products side

 

[BlueGas]

re: HSC Chemistry Marathon Archive

I dont think you need to go into reaction quotient because when the system is at equilibrium, it still can favour one side. From what ive been taught:

K <1 means the point of equilibrium is on the reactants side

K >1 means the point of equilibrium is on the products side

So if you were to write your reasoning for why (for example) the equilibrium is on the reactants side, you would say K < 1? That's it? I've seen HSC sample answer say if K > 10^3 then the equilibrium lies to the products side.