Paper 1 HL questions help!

[allthebest]

I don't understand these P1 questions. Please help me understand them by giving some explanations.

answers:

1. B

- which equation should be used? I thought it was mol= vol/24

2. A

- why is the denominator (0.5)^2? I thought it was C

3. C

- I don't get these types of questions. + means a stronger oxidizing agent and - is strong reducing agent. Then shouldn't the most negative one, Fe2+, be the correct answer?

4. C

- no idea about this...

5. D

- how do you know...

6. A

- I know it is optical, but how do we know if it is or is not geometric?

 

Thank you very much.

Your help will really help me. 

[kw0573]

Because of length of post, I will only provide a brief explanation if I think you can work out the details.
1. Take consideration that 2 mols of sodium bromate(V) produces 3 moles of oxygen.

2. The 2 mols of hydrogren and iodine are not concentration at equilibrium, but initial concentrations. The equilibrium constant uses only equilibrium concentrations.

3. Strongly recommend that you revise redox. H⁺ is reduced, and is at cathode, and reaction proceed as equation 2 is written. The oxidation reaction must happen in the opposite direction as written in question. That limit down to A or C. Spontaneous redox reaction when E(Cathode) - E(anode) > 0. When you flip the reaction, reaction Sn -> Sn²⁺ +2e^- would make the overall reaction positive. + means reactant is strong oxidizing agent. - means product is strong reducing agent. -0.14 is the most negative out of all three reactions. You cannot switch the reactions if you use this rule. 

4. The metal is in ionic form (as an cation). We seek the reaction X⁺ⁿ + ne^- --> X. The most X produced use least amount of electrons per reaction

5. Usually you have to identify the ester linkage (COO). Sometimes they give extra carbons on some choices but here in this case, you only need to know that polymers need a di-carboxylic acid and a di-alcohol, which only D has.

6. Optical relates to stereocenters (R vs S). Geometric (a word now archaic) relates positions with relation to a double bond. The molecule does not have 2 different groups on both sides of the double bond, so there is no geometric isomerism. 
Please reply with questions if you need further clarification. But do try all these questions again first!

Edited April 13, 2017 by kw0573

[ABKor752]

I'm in IB Chem, but at the moment I am only able to answer the first question. (Sorry...)

It gives you that molar volume is 24 dm³ mol^-1, so if you want to get from dm³ of O₂ to moles of O₂, you do the following:

2.4 dm³ O₂ x (1 mol O₂ / 24 dm³ O2) = 0.10 mol O₂

We put the molar volume flipped because the dm³ cancels out that way, leaving the remaining value in moles. From there, we use the equation's coefficients to find moles of NaBrO₃. Since the coefficient of O₂ is 3 and the coefficient of NaBrO₃ is 2, we have the following:

0.10 mol O₂ x (2 mol NaBrO₃ / 3 mol O₂) = 0.067 mol NaBrO₃

Again, the mol O₂ cancel out this way, and thus we are left with mol NaBrO₃. Therefore, the answer is B.

I hoped that helped! Sorry I can't answer the other ones at the moment, but I hope you get the answers soon.

[allthebest]

On 2017. 4. 14. at 1:28 AM, kw0573 said:

Because of length of post, I will only provide a brief explanation if I think you can work out the details.
1. Take consideration that 2 mols of sodium bromate(V) produces 3 moles of oxygen.

2. The 2 mols of hydrogren and iodine are not concentration at equilibrium, but initial concentrations. The equilibrium constant uses only equilibrium concentrations.

3. Strongly recommend that you revise redox. H⁺ is reduced, and is at cathode, and reaction proceed as equation 2 is written. The oxidation reaction must happen in the opposite direction as written in question. That limit down to A or C. Spontaneous redox reaction when E(Cathode) - E(anode) > 0. When you flip the reaction, reaction Sn -> Sn²⁺ +2e^- would make the overall reaction positive. + means reactant is strong oxidizing agent. - means product is strong reducing agent. -0.14 is the most negative out of all three reactions. You cannot switch the reactions if you use this rule. 

4. The metal is in ionic form (as an cation). We seek the reaction X⁺ⁿ + ne^- --> X. The most X produced use least amount of electrons per reaction

5. Usually you have to identify the ester linkage (COO). Sometimes they give extra carbons on some choices but here in this case, you only need to know that polymers need a di-carboxylic acid and a di-alcohol, which only D has.

6. Optical relates to stereocenters (R vs S). Geometric (a word now archaic) relates positions with relation to a double bond. The molecule does not have 2 different groups on both sides of the double bond, so there is no geometric isomerism. 
Please reply with questions if you need further clarification. But do try all these questions again first!

thanks! I'll try for sure

[allthebest]

On 2017. 4. 14. at 1:55 AM, ABKor752 said:

I'm in IB Chem, but at the moment I am only able to answer the first question. (Sorry...)

It gives you that molar volume is 24 dm³ mol^-1, so if you want to get from dm³ of O₂ to moles of O₂, you do the following:

2.4 dm³ O₂ x (1 mol O₂ / 24 dm³ O2) = 0.10 mol O₂

We put the molar volume flipped because the dm³ cancels out that way, leaving the remaining value in moles. From there, we use the equation's coefficients to find moles of NaBrO₃. Since the coefficient of O₂ is 3 and the coefficient of NaBrO₃ is 2, we have the following:

0.10 mol O₂ x (2 mol NaBrO₃ / 3 mol O₂) = 0.067 mol NaBrO₃

Again, the mol O₂ cancel out this way, and thus we are left with mol NaBrO₃. Therefore, the answer is B.

I hoped that helped! Sorry I can't answer the other ones at the moment, but I hope you get the answers soon.

thanks for the clear explanation!