help with Year 11 Questions from the water module :( (2 Viewers)

[stainmepink]

Hello. I need help with 3 year 11 questions, taken from the Conquering Chemistry Book.

Q1. A solution containing silver nitrate was mixed with another solution containing sodium acetate. A white precipitate of silver acetate was formed. In another experiment, silver acetate solid was mixed with water. My question is, if you were given the solubility of silver acetate in the 1st solution, is the solubility of silver acetate the same in the second experiment? In the answers, the book says that the solubility of silver acetate was derived from the experiment, then implemented in the second experiment. I thought u cant compare the solubility of the same solute in two different solvents.

Q2 When a brown iodine solution and a colourless arsenious acid solution (each containing the same number of moles) are mixed, the brown colour of the iodine fades noticeably as the following reaction occurs.

H3AsO3 (aq) + I2(aq) + H2O(l) --> H3AsO4 (aq) + 2H(+)(aq) + 2I(-)(aq)

(H3AsO3 is arsenious acid; H3AsO4 is arsenic acid)

However, the brown colour does not completely disappear. What do you conclude about the reaction? Is it reversible and how can you tell?

Q3 Iron (III) ions react with thiocyanate ions, SCN- to form a blood-red solution:

Fe (3+)(aq) +SCN (-)(aq) --> Fe(SCN)(2+)(aq)

The intensity of the colour is proportional to the amount of Fe(SCN)(2+) ion in the solution. Volumes of two solutions containing 0.0010 mol Fe(3+) and SCN(-) respectively were mixed and then divided equally between two test tubes. To one tube, some extra Fe(3+) was added. If the original reaction had gone to completion, would you expect any change in intensity of the colour when this extra Fe (3+) was added? In fact, the intensity of the colour increased (by reference to the second est tube). What does this tell you about the reversibility or otherwise of this reaction. Explain fully.


thanx to whoever answers my questions, your help will be generously appreciated

 

[pLuvia]

Hello. I need help with 3 year 11 questions, taken from the Conquering Chemistry Book.

Q1. A solution containing silver nitrate was mixed with another solution containing sodium acetate. A white precipitate of silver acetate was formed. In another experiment, silver acetate solid was mixed with water. My question is, if you were given the solubility of silver acetate in the 1st solution, is the solubility of silver acetate the same in the second experiment? In the answers, the book says that the solubility of silver acetate was derived from the experiment, then implemented in the second experiment. I thought u cant compare the solubility of the same solute in two different solvents.

Q2 When a brown iodine solution and a colourless arsenious acid solution (each containing the same number of moles) are mixed, the brown colour of the iodine fades noticeably as the following reaction occurs.

H3AsO3 (aq) + I2(aq) + H2O(l) --> H3AsO4 (aq) + 2H(+)(aq) + 2I(-)(aq)

(H3AsO3 is arsenious acid; H3AsO4 is arsenic acid)

However, the brown colour does not completely disappear. What do you conclude about the reaction? Is it reversible and how can you tell?

Q3 Iron (III) ions react with thiocyanate ions, SCN- to form a blood-red solution:

Fe (3+)(aq) +SCN (-)(aq) --> Fe(SCN)(2+)(aq)

The intensity of the colour is proportional to the amount of Fe(SCN)(2+) ion in the solution. Volumes of two solutions containing 0.0010 mol Fe(3+) and SCN(-) respectively were mixed and then divided equally between two test tubes. To one tube, some extra Fe(3+) was added. If the original reaction had gone to completion, would you expect any change in intensity of the colour when this extra Fe (3+) was added? In fact, the intensity of the colour increased (by reference to the second est tube). What does this tell you about the reversibility or otherwise of this reaction. Explain fully.


thanx to whoever answers my questions, your help will be generously appreciated

where u up to water module lol.. we just started.. is conquering chemistry gud??

 

[thunderdax]

Q1. In the first experiment, both reactants were originally solutions, which means they were in water. When silver acetate formed it was insoluble in the water which was present which means it will be insoluble in another sample of water under the same conditions. In answer to your question, they are both the same solvent: water.

Q2. The left side of the equation makes the solution go brown while the right makes it go clear. Since it fades to a lighter brown, it must be in between the two endpoints of the reaction. This means it is in equilibrium, meaning it is a reversible reaction.

Q3. I don't quite understand this question, as I wouldn't expect it to change colour when more thiocynate is added.

 

[Jumbo Cactuar]

Q3 Iron (III) ions react with thiocyanate ions, SCN- to form a blood-red solution:

Fe (3+)(aq) +SCN (-)(aq) --> Fe(SCN)(2+)(aq)

The intensity of the colour is proportional to the amount of Fe(SCN)(2+) ion in the solution. Volumes of two solutions containing 0.0010 mol Fe(3+) and SCN(-) respectively were mixed and then divided equally between two test tubes. To one tube, some extra Fe(3+) was added. If the original reaction had gone to completion, would you expect any change in intensity of the colour when this extra Fe (3+) was added? In fact, the intensity of the colour increased (by reference to the second est tube). What does this tell you about the reversibility or otherwise of this reaction. Explain fully.

Fe (3+)(aq) +SCN (-)(aq) is an equilibrium reaction since it is a reaction yet isn't 100% yield (given "In fact, the intensity of the colour increased" ~ even though 1:1 ratio of reactants). Since it is an equilibrium reaction it is reversible.

There is one flaw in the question since adding more Fe 3+ involves adding more solvent. This decreases the apparent intensity of the colour in a test tube. So this is in fact not always the case and is a function of concentration of the reactants (would post mathematics, but it is about three pages worth that would be lost on most).

 

[thunderdax]

Question - "If the original reaction had gone to completion..."
Doesn't this means it does have a 100% yield?

 

[Jumbo Cactuar]

Question - "If the original reaction had gone to completion..."
Doesn't this means it does have a 100% yield?

I think it means it is at equilibrium. Completion as in no more reaction, though even that is silly since it is always reacting!

 

[princessj]

aaahhh!!!!! ur hurting me! this ugly stuff brings bad memories of my ugly chem classes

 

[Jumbo Cactuar]

Also Q.2 is a redox reaction so an applied voltage would favour one side or the other, that is assuming you had the system setup correctly. Though that isn't really a concern of yr 11 is it?

 

[Dreamerish*~]

I'm shocked. When I first read the questions I had next to no idea. Now that I read it again after studying and sitting for my chemistry trial, it all seems to make perfect sense.

 

[Jumbo Cactuar]

Q1. The solubilities depend on the amount/type of dissolved molecules in the solvent and temperature. Silver acetate will dissolve 1.11% (w/w) in deionized water at standard conditions. It is something like an additional 10K doubles reaction rates, and since partial solubility is an eq reaction I think that also applies. What I am saying is that the method certainly doesn't qualify for a valid analytical technique!