O Levels Chemistry – Selected Exam Questions Cont’d

03 Apr

Posted by: sean in: Chemistry Notes & Tips

I will be sharing with you another 2 questions that test O Level Chemistry students on their concepts understanding.

Again, these 2 questions were sent in via our own coaching students via email. I applaud him for taking actions in sending me emails to clear his doubts. This platform has been well received by our students over the years. (You can check the previous 2 questions by him over HERE)

The 2 new questions are:

Question 1: on REDOX Reactions

A science guru said “Hydrogen peroxide is oxidized and reduced at the same time during its decomposition”.

Prove the validity of the above statement using your knowledge in Redox, in terms of changes of oxidation states.

Suggested answer by Student X:

My answer is: When hydrogen peroxide is decomposed, it loses hydrogen, which means the oxidation state of oxygen increases to +2. It also loses oxygen, which means the oxidation state of hydrogen is -2. Hence, hydrogen peroxide is oxidized and reduced at the same time during its decomposition.

Is this answer correct?

Question 2: on Rate of Reaction

Explain in terms of particles, how temperature would affect the rate of reaction.

Suggested answer by Student X:

My answer is: When the temperature increases, the speed of its particles increase, hence increasing the frequency of effective particle collision. Thus, the rate of reaction would increase.

Is my answer correct?

Do you agree with the above answers by Student X?

The best way to learn is to work the answers out on your own and prove to yourself that it is correct.

Confucius famous quote: “I hear and I forget. I see and I remember. I do and I understand.”

PS: Work out the answers, and leave your answers (and reasonings) in the “LEAVE A REPLY” section below. I will come in to give my suggested answers soon.

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11 Responses

hina
06|Apr|2009 1

sir i need your help? if i have any question shall i e-mail you my querries? please help me sir!!

Reply
sean Reply:
April 22nd, 2009 at 12:49 am
Hi Hana,

Please send in your questions to admin@SimpleChemConcepts.com.

In view of the sheer amount of emails we received per day, our response might take a while.

Hear from you.

Cheers
Sean Chua
Master Trainer & Author
WINNERS Education Group

Reply
hina
18|Apr|2009 2

Question 2: on Rate of Reaction

Explain in terms of particles, how temperature would affect the rate of reaction.

when the temperature increases the kinetic energy of the particles increases.they
collide faster with each other reasulting in more effectice coolisions and thus the rate
of reaction increases

Reply
sean Reply:
April 24th, 2009 at 2:27 pm
Hi hina,

I thought that is a pretty good answer.

Keep up the good work.

Are you taking O Levels Chemistry Exams also?

To Your Academic Success in Chemistry.
Sean Chua
Master Trainer & Author
WINNERS Education Group

“Experience Learning with A Difference”

Reply
hina
18|Apr|2009 3

Question 1: on REDOX Reactions

A science guru said “Hydrogen peroxide is oxidized and reduced at the same time during its decomposition”.

Prove the validity of the above statement using your knowledge in Redox, in terms of changes of oxidation states.

Suggested answer by hina……

My answer is: When hydrogen peroxide is decomposed, it loses hydrogen, which means the oxidation state of oxygen increases to +2. It also loses oxygen, which means the oxidation state of hydrogen is -2. Hence, hydrogen peroxide is oxidized and reduced at the same time during its decomposition.

Reply
sean Reply:
April 24th, 2009 at 3:06 pm
Hi hina,

Glad you are participating.

However, ur description of the oxidation of H and O atoms as Hydrogen Peroxide decomposes is not correct.

Perhaps, you can try again using the following chemical equation for decomposition of hydrogen peroxide:

2 H2O2 –> O2 + 2 H2O

Try it out and let me know what happens to the oxidation states of H and O atoms as hydrogen peroxide decomposes.

Hear from you.

To Your Academic Success in Chemistry.
Sean Chua
Master Trainer & Author
WINNERS Education Group

“Experience Learning with A Difference”

Reply
hina
24|Apr|2009 4

i think that since the oxidation state of hydrogen is decreasing from +4 to +1 so it is being reduced but
h2 is gaining oxygen at the same time so it is being oxidised. so i think it os right
to say that h2o2 is being oxidised and reduced at the same time.

Reply
S-N
23|Aug|2009 5

In peroxide, O has a state of -1 while in H2O & O2 , it has a state of -2. Here, it is being reduced.

To form O2, the peroxide loses hydrogen atom, hence it is considered as oxidation .

Not very sure if it is correct, tho.

Reply
S-N
24|Aug|2009 6

Amended
In peroxide, O has a state of -1 while in H2O , it has a state of -2. In O2, it has a state of 0.

Hence, there is oxidation and reduction occuring at the same time.

Reply
Tingwei
27|Sep|2009 7

For question 2)
When the temperature increases,the kinetic energy of the particles also increase,and subsequently they’re able to collide more often.Thus,effective collision increases leading the increasing of ROR.Pls correct me, Sir..Thanks

Reply
Wasiq
11|Jan|2010 8

Question no 2 answer:
The increase in temperature will lead to increase in kinetic energy which ultimately leads to more effective collisions between molecules.

Reply