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

UBC 化学家教

多年经验辅导UBC一年级和二年级各科化学，包括CHEM 111, CHEM 113, CHEM 121. CHEM 123, CHEM 205, CHEM 211 和 CHEM 233. 可用中英文双语教学，助你理解重点，取得好成绩。请与张博士联系，手机604-808-6827， 电邮：vancouverchemistrytutor@gmail.com

张老师化学家教

首先祝贺张老师的同学们在五月份的AP化学和六月份SAT化学考试中取得了好成绩。
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

张老师化学家教

首先祝贺张老师的同学们在五月份的AP化学和六月份SAT化学考试中取得了好成绩。
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 --63

Welcome back to my blog. Following is Question 62 I posted earlier.

 

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

The correct answer is D. This a tough question to most students because I found a lot of students studying AP know little about predicting product of reactions. 

First of all , we need to figure out which one of them will react with dilute hydrochloric acid and generate a gas. Zn is an active metal and will react with dilute acid and produce hydrogen gas. For B, C, and D, they will undergo double replacement reactions with dilute HCl and produce a salt and another acid. Both HNO3 and HBr are strong acid and stay in aqueous solution. But H2CO3 is a weak acid and it decomposes to CO2 and water. 

Now we need to figure out which one of them H2 or CO2, is denser than air?

According to Avogadro's Law, at the same temperature and pressure, any gas has a same volume. While density is defined as mass per volume, the higher the molecular weight, the denser it is, since their molar volume is the same. Air has an average molecular weight of 29, H2 is 2 and CO2 is 44. Thus CO2 is denser than air, D is the correct answer.

Following is question 63 of the series:

63.  A 20.00 mL sample of a Ba(OH)2  solution is titrated with 0.245 M HCl. If 27.15 mL of HCl is required, what is the molarity of the Ba(OH)2  solution?
(A)  0.166 M
(B)  0.180 M

(C)  0.333 M
(D)  0.666 M

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 --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 --61

Welcome back to my blog. here is Question 60 I posted earlier.
60. Glycerol has lower vapour pressure than does ethanol at room temperature. Which of glycerol and ethanol has the lower boiling point?

The correct answer should be ethanol.

Vapour pressure is the pressure of the vapour when at a certain temperature the liquid and the vapour reach equilibrium in a closed container. Vapour pressure is only dependent on the nature of the substance and temperature. For a given substance, its vapour pressure is only dependent on temperature.  As temperature increases, vapour pressure increases. When the vapour pressure reaches the atmosphere pressure, the temperature is defined as boiling point. As a result, the higher the vapour pressure, the lower the boiling point.

Following is question 61 of the series:

 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.

I will post the answer in my next blog.
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.