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!

AP Chemistry Question of the Day--52

Welcome back to my blog. The answer to question 51 is B. According to the Lowry-Brønsted definitions, acids are proton donors and bases are proton acceptors. If a species can both donate and accept a proton, it is called amphiprotic. Answers A and C can only be acids and answers B and D can only be bases.
Here is question 52 of the series:
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?

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 --51

Welcome back to my blog. The correct answer for Question 50 is A. As you go from left to right in the same period, more effective nuclear charge is experienced. As a result, you will see smaller radius, higher ionization energy, higher electron affinity and higher electronegativity. There is no doubt that atomic mass is increasing because of the increased atomic numbers.
Here is question 51 of the series:
51.  According to the Lowry-Brønsted definitions, which chemical species can function either as an acid and as a base, depending on the conditions?

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 of the day--50

As I am getting less busy, I will resume my series of chemistry question of the day. Here is my last question I posted last November.

49. What is the solubility of lead (II) bromide at 298K if Ksp of lead (II) bromide is 6.6x10-6?

The solubility equilibrium of lead (II) bromide can be represented as:

and the Ksp can be expressed as 

assume the solubility of lead (II) iodide is xM, then

by solving the equation we can find the solubility of lead (II) iodide to be 1.2x10-2. Pay attention here that I keep 2 significant figures for my answer as the original kip in the question has two sig figs.

Here is question 50 of the series:

50. which of the following properties generally decrease across the periodic table from Na to Cl?

A. atomic radium

B. Atomic mass

C. electronegativity

D. first ionization energy

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!

How to do well in chemistry exams?

Finally this year's AP chemistry exam is over. This is the first year with the new curriculum framework in place. I am glad that all my students did well in the exam. I attribute that to their hard work and our all around review of the material.
Often people ask me, chemistry is so hard, how can I do well in exams like AP and SAT II chemistry?
Well I can tell you a few key points to make this possible.
1. Understand the key concepts instead of trying to remember them. A lot of people think chemistry is hard because there are so much to memorize. I do not totally agree. If you understand the concepts well, you do not need to remember a lot of stuff. There are some stuff you need to remember, like the flame colours of alkali metal ions which has no trend or clue whatsoever. Most of the stuff in chemistry though can be logically reasoned. In chemistry there are a few concept to keep in mind.

• chemistry is all about electrons. The driving force for bond formation and reaction is for all the elements to attain noble gas configuration. 
• All the interaction can be related to Coloumb attractions between particles. you can use Coloumb attractions to reason ionic bond strength, intermolecular forces and physical properties trend and so much more.
• Lower energy and higher entropy are important driving forces for reactions to happen.

2. Deepen your understanding of the key concepts by practice. Sometimes, you think you got it, but to get it right, practice is very necessary.
3. what is most important in learning chemistry is to connect what is in the book with everyday life. When something your learned in books can be applied to your daily life, you will find it intriguing and fun. And interest and curiosity can lead you to learn more. We all know solution has a higher boiling point that pure solvent. Have you thought of adding a little bit of salt when you boil spaghetti to save time cooking? the raised boiling point will help. Also how does pressure cook work?
If there is a spill of baking soda, what do we use to clean it up?
I hope these points can help new chemistry learners start their journey with fun and easiness.
If you have any comment, feel free to shoot me an email. My email address is vancouverchemistrytutor@gmail.com

Langara Chemistry Tutor

Experienced Ph. D. in chemistry offering tutoring service for CHEM 1114, 1118, 1120 and 1220. Personalized tutoring tailored to individual needs. Guaranteed improvement and success.  I can teach with both English and Chinese. For your tutoring needs, please call Dr. Zhang  at 604-808-6827.

南开大学化学博士，UBC化学系博士后多年经验辅导CHEM 1114, 1118, 1120, 1220 . 因材施教，帮你理解重点，抓住要点，取得满意考试成绩。可用中英文双语沟通。

如果您有辅导需求，请随时与我联系 604-808-6827。

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.

For your tutoring needs, please call Dr. Zhang  at 604-808-6827.

南开大学化学博士，UBC化学系博士后多年经验辅导CHEM 111, 113, 121, 123, 205, 233. 因材施教，帮你理解重点，抓住要点，取得满意考试成绩。可用中英文双语沟通。 如果您有辅导需求，请随时与我联系 604-808-6827。

张老师化学家教

Experienced Ph. D. in chemistry offering tutoring service for AP Chemistry, IB Chemistry, SAT II Chemistry, Chemistry 11 and Chemistry 12.  Personalized tutoring tailored to individual needs. Guaranteed improvement and success. 

I can tutor with both English and Chinese.

For one on one tutoring needs, please call 604-808-6827.

南开大学化学博士，UBC化学系博士后多年经验辅导AP化学，IB化学， SATII化学，十一年级和十二年级化学， 因材施教，帮你理解重点，抓住要点，取得满意考试成绩。可用中英文双语沟通。请电604-808-6827与张老师联系。