AP Chemistry Question of the Day --59

Welcome back to my blog. Following is question 58 of the series I posted yesterday:

58. A mixture of 64g oxygen and 66g of CO₂ are contained in a vessel exerting a total pressure of 980mmHg. Find the pressure exerted by each gas?

According to Dalton's Law of partial pressure, the pressure of a gas mixture is the sum of the partial pressures of the individual components of the gas mixture. As the mixture share the same container, the gases have the same volume and temperature. 

From the Ideal Gas Law. PV=nRT, the partial pressure of each gas is directly proportional to its mole number. If total pressure is known, the partial pressure of each gas would be the total pressure times its mole fraction.

Hope you understand this. Following is question 59 of the series:

59.  Which of the following best helps to account for the fact that the F^- ion is smaller than the O^2- ion?                                                     

(a) F^- has a larger nuclear mass than O^2-    

(b) F^- has a larger nuclear charge than O^2-   

(c) F^- is more electronegative than O^2-        

(d) F^- is more polarizable than O^2-.

I will post the answer in my next post.

Thank you very much for visiting my blog. I am available to discuss any topics in Chemistry at all levels. Please shoot me an email at vancouverchemistrytutor@gmail.com or give a call at 604-808-6827.

AP Chemistry Question of the Day --56

Welcome back to my blog. Here is question 55 I posted earlier. 
55. Aqueous solutions of AgNO3, Cu(NO3)2 and Cr(NO3)3 are electrolyzed using the same quantity of electricity. How do the number of moles of metal formed compare?

A.      Ag = Cu = Cr

B.      Ag > Cu > Cr

C.      Ag < Cu < Cr

D.      Cu > Ag > Cr

The correct answer is B. To answer this question, we need to understand how electrolysis works. In an aqueous electrolytic cell, redox reaction happens so that the cation of the salt or hydrogen ion from water is reduced to its elemental form and the anion or hydroxide from water is oxidized to its oxidation product or oxygen. Whether water will be involved depends on the reduction potentials of the cation and the anion. If the anion has a lower reduction potential than hydroxide, then its oxidation is dominant. If the cation has a higher reduction potential than hydrogen, its reduction is then dominant. Also we need to take into account of the pH and over potential effect of water. In this question, since all of the metal ions have higher reduction potential than hydrogen, they are going to be reduced. As diver ion, cooper ion and chromium ion has a charge of +1, +2 and +3 respectively, to get one mole of metal reduced, they will need 1, 2 and 3 moles of electrons respectively. If the same amount of electricity is consumed, then the mole number of the metals would be: 1mole Ag:0.5mole Cu:0.33mole chromium. Thus, B is the correct answer.

Following is question 56 of the series:

56. 

I will post the answer in my next blog.

Thank you very much for reading my post, I am available to discuss any topics in chemistry. Please give me a call at 604-808-6827 or email me at vancouverchemistrytutor@gmail.com. My website is located at www.vancouverchemistrytutor.com.

Regards!

AP Chemistry Question of the Day --55

Welcome back to my  blog. Here is question 54 I posted yesterday. The correct answer is B.

There are several factors affecting reaction rate such as temperature, concentration, surface area and catalyst. But here what is being tested is the collision theory.
For a chemical reaction to happen, the reactant molecules have to collide with enough energy and proper orientation. If the reactants molecules are easier to bump into each other, the reaction should occur relatively faster. As a result, from the four choices above, B is the correct answer. A and D are reactions in gas phase. Gas molecules are far apart and are not likely to collide as easily as in solution. C is a heterogeneous reaction. Again the reaction is limited at the surface of the lead.

Following is Question 55 of the series,

55. Aqueous solutions of AgNO3, Cu(NO3)2 and Cr(NO3)3 are electrolyzed using the same quantity of electricity. How do the number of moles of metal formed compare?

A.      Ag = Cu = Cr

B.      Ag > Cu > Cr

C.      Ag < Cu < Cr

D.      Cu > Ag > Cr

I will post the answer in my next blog.

Thank you very much for reading my post, I am available to discuss any topics in chemistry. Please give me a call at 604-808-6827 or email me at vancouverchemistrytutor@gmail.com. My website is located at www.vancouverchemistrytutor.com.

Regards!

AP Chemistry Question of the Day --53

Welcome back to my blog. Here is question 52 I posted yesterday.

52. An 11.1L sample of 0.25mol oxygen gas is converted to ozone. If all the oxygen is converted to ozone, what will the volume of ozone be?

This is a typical stoichiometry question. To solve the question, we have to correctly write the chemical equation and properly balance it.  Ozone and oxygen are allotropes (do you still remember what is allotropes? Allotropes are different forms that an element can exist in) of oxygen and their formula are O3 and O2 respectively.

The balanced chemical reaction should be:

According to the chemical equation, 3mol of oxygen gas will produce 2mol of ozone gas. as a result, 0.25mol of oxygen should produce:

What is the volume of the ozone gas then? Recall Avogadro's law which states that  at constant temperature and pressure, the volume is directly proportional to the mole number. Since 0.25mol oxygen occupies 11.1L. apparently it is not STP. Or else, it should be approximately 0.5mol roughly 11.2L.  We know for ideal gas, the identity of the gas does not matter. As long as they have the same mole numbers, at the same T and P, the volume would be same. As a result, the volume of the ozone would be:

Pay attention that I kept 2 sig figures for my answer because the mole number of ozone has 2 sig fig.

In stoichiometric calculations, dimensional analysis is key. Make sure you align your expressions properly so that the unit can cancel out and only left with what you are asked for.

Here is Question 53 of the series:

53.  A solution appears yellow.  It must be absorbing in the  

    (a) yellow only    (b) red only    (c) green only    (d) blue only   (e) purple only. 

 I will post the answer in my next blog.

Thank you very much for reading my post, I am available to discuss any topics in chemistry. Please give me a call at 604-808-6827 or email me at vancouverchemistrytutor@gmail.com. My website is located at www.vancouverchemistrytutor.com.

Regards!

UBC Chemistry Tutor

Experienced Ph. D. in chemistry offering tutoring service for CHEM 111, 113, 121, 123, 205 and 233.  Personalized tutoring tailored to individual needs. Guaranteed improvement and success.  I can teach with both English and Chinese.

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