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Re: O-Level Chemistry

Posted: Mon Mar 16, 2020 5:13 pm
by bestwishes
The answer is in the Chem textbook, Topic electrolysis

Re: O-Level Chemistry

Posted: Mon Mar 16, 2020 5:16 pm
by bestwishes
achun708 wrote:
Mon Mar 16, 2020 2:15 pm
Hello Everyone,

Can you please help me with this? My son is a bit confused with this problem and me too. Thanks.

Predict the products formed (i) at the cathode, (II) at the anode, when copper (II) sulfate solution is electrolysed using carbon electrodes.
The answers can be found in Chem Matters textbook. Topic electrolysis pg 293

Re: O-Level Chemistry

Posted: Wed Mar 18, 2020 11:32 pm
by Nefertari
Yep, the answer is in the Chem Matters textbook. Or you can ask everybody's best friend Google:

http://www.docbrown.info/page01/ExIndCh ... stry04.htm

Electrolysis of copper sulphate using carbon (graphite) electrodes vs using copper electrodes . It's a typical case study (so bascially, you need to understand the full process).

Few things to note in electrolysis:
1. Cations are attracted to the cathode and anions are attracted to the anode.
2. Electrolysis requires electricity flowing through the electrodes to split up the electrolytes (conducting liquid containing the compound, eg copper sulphate).
3. Is the electrode used inert or does it react with the electrolyte?

In the case of copper sulphate, what occurs at the cathode is simple and straightforward: COPPER is deposited ON the cathode (negative terminal) due to as the Cu2+ ions get reduced and becomes neutral copper atoms.

At the anode, two scenarios can occur. If the electrode is copper, it is reactive with the sulphate ions that are attracted to the copper anode and thus the copper anode dissolved. However, the question states that CARBON (inert electrodes) are used, therefore the sulphate ions (produced during the electrolysis) attracted at the anode remains stable. What you get are hydroxide ions (which are also attracted to the anode) getting oxidised to discharge water molecules and also form oxygen.

Just read it a couple more times and it will come to you. Cheers!

Re: O-Level Chemistry

Posted: Wed Mar 18, 2020 11:36 pm
by Nefertari
Metanoia wrote:
Wed Sep 06, 2017 9:26 pm
kitty2 wrote:
Metanoia wrote:
Hi there, to clarify, are you referring to the school-based Science Practical Assessment taken by Pure chemistry students or the Science Practical Exams taken by combined chemistry students?
Is for combine science students :) . Thanks
Combined chemistry students will most likely be doing identification of unknown ions.

1) It will be useful for the student to be familiar with this reference table.
It is page 36 in this document.

http://www.seab.gov.sg/content/syllabus ... 8_2017.pdf

This table will be provided during the practical, but I'll encourage them to be familiar with it before hand rather than try to make sense of it during the test itself.

2) Basically, the test consists of following the instructions, writing down the observations and making conclusions.
Writing observations - the student can use the relevant phrases described in the table
Making conclusions - this part is largely dependent on the observations.

Students are usually stressed about making the conclusion but keeping things in perspective. The chemistry practical is "only 7.5%" and the conclusion part is an only small portion. There are more marks to make up for it in the theory papers.

3) The questions are quite varied, so I will not try to "predict" anything more specific. I've seen past year papers on O-level practicals available in the bookshop, you can buy them to have a sense of the questions.
If however, you have specific questions, feel free to clarify.
This is a very good post. Two thumbs up :)

Re: O-Level Chemistry

Posted: Mon Mar 23, 2020 1:24 pm
by uptas
achun708 wrote:
Mon Mar 16, 2020 2:15 pm
Hello Everyone,

Can you please help me with this? My son is a bit confused with this problem and me too. Thanks.

Predict the products formed (i) at the cathode, (II) at the anode, when copper (II) sulfate solution is electrolysed using carbon electrodes.
Hello achun. The ANSWER to this problem is below.

Ions present:

From copper (II) sulfate: Cu2+ ions and SO4 2- ions

From water: H+ ions and OH- ions.


(i)

At cathode, Cu2+ and H+ ions are present.

Cu2+ ions are selectively discharged to form copper metal.

Cu2+ (aq) + 2e- will produce Cu (s)




(ii)

At anode, OH- and SO4 2- ions are present.

OH- ions are selectively discharged to form oxygen gas.

4OH- (aq) will produce 2H2O (l) + O2 (g)+ 4e-


Thanks!

Re: O-Level Chemistry

Posted: Mon Mar 23, 2020 1:58 pm
by achun708
Thank you son much Nefertari, Uptas and bestwishes! :-)

Re: O-Level Chemistry

Posted: Fri Apr 03, 2020 8:09 pm
by uptas
Important Notes Related to Speed of Reaction:

1. The speed of reaction is the amount of reactant used up or the amount of product obtained per unit time.

2. Activation energy is the minimum energy that the reacting particles must possess for a reaction to occur.

3. An effective collision is a collision that is successful in producing a chemical reaction.

4. A catalyst is a substance that increases the speed of a chemical reaction.

5. An enzyme is a substance that catalyses biochemical reactions (chemical reactions in plants and animals).

Re: O-Level Chemistry

Posted: Sun Apr 05, 2020 7:47 pm
by uptas
Factors Affecting Speed of Reaction

1. The smaller the particle size

* the larger is the total surface area exposed to collisions
*the higher is the frequency of effective collisions
*the greater is the speed of reaction


2. The higher the concentration of the reactant

*the greater is the number of particles per unit volume
*the higher is the frequency of effective collisions
*the greater is the speed of reaction.


3. The higher the pressure of gaseous reactants

*the smaller is the volume
*the greater is the number of particles per unit volume
*the higher is the frequency of effective collisions
*the greater is the reaction.

Pressure has no effect on reaction that do not involve gases.


4. At higher temperature

*the reactant particles absorb energy and move faster
*more reactant particles have the minimum activation energy to react
*the number of effective collisions increases
*the greater is the speed of reaction.


5. Presence of Catalyst or Enzyme

*a catalyst provides an alternative route that requires a lower activation energy
*more reactant particles can overcome the lower activation energy
*this increases the frequency of effective collisions and hence the speed of reaction increases

Re: O-Level Chemistry

Posted: Sun Apr 12, 2020 1:44 pm
by uptas
Hello there!
Let's learn Organic Chemistry!

1st PART:
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Re: O-Level Chemistry

Posted: Wed Apr 29, 2020 11:01 am
by chemanywhere15
Learning Organic Chemistry

Part 2:


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