CHEM 121 and CHEM 233 tutor

Final exam is coming soon, if you need help with your CHEM 121 or CHEM 233, do not hesitate to contact me at 604-808-6827. No matter you goal is to get a higher A or just to pass, I can help you accomplish it.

UBC Chemistry Tutor

September again. I am an experienced chemistry tutor. I can help you with your UBC CHEM 121, CHEM 123, CHEM 233, CHEM 205, CHEM 203 and CHEM 213. No matter your goal is to pass or ace to get into medical school, I can help you. If you need a tutor, give a call at 604-808-6827.

UBC chemistry tutor

The new UBC summer term is coming very soon. If you need help with CHEM 121/123. CHEM 233/205, please call me at 604-808-6827 and I am more than happy to help you meet your goals.

Dr. Zhang Chemistry Tutoring 张老师化学家教

Ph. D in Chemistry with years of experience offering chemistry tutoring on AP Chemistry, IB Chemistry, SAT Chemistry, Chemistry 11 and 12, University Level General Chemistry and second year Organic Chemistry including UBC CHEM 111, CHME 113, CHEM 121, CHEM123, CHEM 154, CHEM 203, CHEM 213, CHEM 233, CHEM 205, CHEM 235 and CHEM 245, Langara College CHEM 1114, CHEM 1118, CHEM 1120 and CHEM 1220. I can teach with both English and Mandarin. Please call 604-808-6827. 南开大学化学系博士，UBC化学系博士后，多年经验辅导AP化学，IB化学，SAT化学，十一年级和十二年级化学,大学一年级普通化学和二年级有机化学和物理化学，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。请电604-808-6827.

UBC Chemistry Tutor

Experienced Ph. D. in chemistry offering tutoring service for UBC CHEM111. CHEM113, CHEM121, CHEM123, CHEM233, CHEM 235, CHEM 205, CHEM 203, CHEM 213, CHEM 235 and CHEM 245. Personalized tutoring tailored to individual needs. Guaranteed improvement and success.  
For your tutoring needs, please call Dr. Zhang at 604-808-6827. 

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

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 --54

Welcome back to my blog. Following is Question 53 I posted earlier. The correct answer is E.

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 am always surprised when my students are confused with colours. As we know, the sunlight consists of UV, visible and infrared lights. The visible region is white (or colourless) when combined. It is actually a mixture of all the colours of the rainbow: red, orange, yellow, green, blue and purple. If a subject appears to be white, then it absorbs no visible light and reflects all the colours. If a subject appears to be black, then it absorbs all the colours of the visible region. If a subject appears a particular colour, for example yellow as stated in the above question, then it reflects only yellow light and absorbs the rest of the colours. The colour that was absorbed should be complimentary to yellow, which means when combined with yellow, it will be black. What colour is absorbed then:
There are three primary colours: red, yellow and blue, as shown below:

If only yellow light was reflected, then red and blue was absorbed and the combination of red and blue is purple. As a result, purple light was absorbed.

Following is question 54 of the series:














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.

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。