AP Chemistry Question of the Day --65

Long time no see. It has been a while  since I last wrote on my blog. The 2016 AP exam is done and I personally think this year the free response questions are easier than last year. I would expect a higher  percentage of 5 overall.
Here comes Question 65 of the series:

Q 65: Which of the following factors would affect vapour pressure:
I. Identity of the substance;
II. Temperature
III. Shape of the container
IV. Size of the container
A. I and II
B. I and III
C. I, II and III
D. all of them

The correct answer is A. Vapour pressure indicates a substance's tendency to evaporate. substance with higher intermolecular force tends to have lower vapour pressure. Also the vapour pressure is only dependent on the temperature for a given substance and size and shape of the container will not affect vapour pressure since it represents the ability of the substance to evaporate. Pressure itself is an intensive property.

Let me know if you have a particulate question regarding AP chemistry or any question regarding chemistry and I am more than happy to discuss with you.

AP Chemistry Question of the Day --65

Welcome back to my blog. Since most schools are doing the unit on acid and base at this time of the year and here is another question related to this topic.

Question 65: Four acids HA, HB and HC and HD solutions have the same pH, which of the following statements is correct:
A. They all have the same concentration
B. They are all strong acids
C. They are all weak acid
D. not enough information to make any conclusion

The correct answer is D. pH represents the concentration of hydronium ion in solution. The pH if an acidic solution is dependent on both the Ka and the concentration of the acid. A solution of a strong acid can have a higher pH due to lower concentration and a solution of a weak acid cna have a lower pH due to higher concentration.

Hope this helpful.

Thank you for visiting my blog. If you have any comments or questions that you would like to be answered, please leave a massage and I will take care of it.

化学家教 Chemistry Tutor

化学家教多年经验专业辅导各个级别的化学课程，包括十年级科学，十一年级和十二年级化学，AP化学， IB化学，SAT化学UBC和LANGARA大学一年级普通化学和大学二年级有机化学，物理化学和分析化学。张老师从南开大学化学系博士毕业，在UBC化学系工作8年，具有牢固的化学知识基础和丰富的实际工作经验，如果您有家教需要，请和张老师联系，电话：604-808-6827， 电邮：vancouverchemistrytutor@gmail.com

AP Chemistry Question of the Day --62

Welcome back to my blog. Following is Question 61 I posted earlier.

 61. In an experiment to determine the percentage of water in a solid hydrate by heating, what is the
best indication that all the water has been removed?
(A)  The solid melts.
(B)  The solid changes color.
(C)  Water vapor no longer appears.
(D)  Successive weighings give the same mass.

The correct answer is D. The water in a  hydrate can be removed by heating. As the water is removed, the mass of the sample will decrease. If successive weighings give the same mass, this means all the water has gone. Depending on what size of your sample is, you may not be able to observe water vapour. As a result, C is not correct even though it looks reasonable. Some of the solid will change colour while some do not, B is not always true. A is not correct because it is not related to water removing. When the solid melt, it is at its melting point and that is all you know. 

Following is question 62 of the series:

 62. Which solid reacts with dilute hydrochloric acid at 25 °C to produce a gas that is more dense than air?

Thank you very much for reading my blog. I am available to discuss any questions regarding all levels of chemistry. Please give me a call at 604-808-6827 if you need any assistance.

AP Chemistry Question of the Day --58

Welcome back to my blog. Here is question 57 I posted earlier:

The correct answer is C. This is a typical chemical equilibrium question. According to Le Chaterlier's Principle, when there is a disturbance applied to an equilibrium, the equilibrium will shift to the direction to minimize the disturbance. From the graph, it can be seen that hydronium concentration decreased. This indicate the equilibrium shifted to the left. 

Addition of HCl will increase hydronium concentration since HCl is a strong acid and it dissociate into hydronium ion and chloride ion when dissolved in water. 

Since the reaction is exothermic, decreasing the temperature will shift it towards the products. As a result, hydronium concentration will increase.

Change in volume only shifts equilibrium involving gas. As there is no gas in this equilibrium, volume will not affect the equilibrium.

Following is question 58 of the series:

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?

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.

张老师化学家教

首先祝贺张老师的同学们在六月份SAT化学考试中取得了好成绩，SX同学取得了800分满分。
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， 大学一年级普通化学，大学二年级有机化学和物理化学，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。
张老师的个人网页：www.vancouverchemistrytutor.com
张老师的博客：http://vancouverchemistry.blogspot.ca

AP Chemistry Question of the Day --57

Welcome back to my blog. Here is question 56 I posted earlier:

The correct answer is B. From the potential diagram, it can be concluded that the products have lower potential energy than the reactants and the reaction is exothermic. According to La Chatellier's Principle, the equilibrium will shift to endothermic side when temperature is increased. The endothermic direction is the reverse of the above direction. Since equilibrium shifts to left, the K will decrease.

Following is question 57 of the series:
57.

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!

Congratulations to my hard working students

I am so happy today that I heard back from my three students who sat the June 8th SAT II Chemistry exam got  scores of 800, 770 and 740. All of them were first time takers of the exam. Good job! I am so proud of you.

AP化学小班辅导

跃跃欲试要参加明年的AP化学考试吗？ AP考试的成绩不仅可以证明你的学习能力，而且可以帮助你免修部分大学课程，给你更多的时间去学习更多的东西。 AP成绩是5分制，5分是大家努力的目标。
我多年辅导AP化学，熟识去年刚刚推出的新的考试大纲，备有大量复习资料，因材施教，深入浅出，中英文结合，帮你理解要点，抓住重点，取得满意成绩。
我计划九月份推出两个AP化学辅导小班，每班限最多四名同学：
2014年9月20日起，每周六下午2点到4点
2014年9月21日起，每周日下午2点到4点
名额有限，请尽快致电张老师604-808-6827，或电邮vancouverchemistrytutor@gmail.com报名
张老师的个人博客： http://vancouverchemistry.blogspot.ca
张老师的网页： www.vancouverchemistrytutor.com
一对一单独辅导，请随时和张老师联系。