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.

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 --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.

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!

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--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!

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。