Monthly Archives: September 2008

O Level Chemistry – Strategies to Predict Products of Electrolysis for Aqueuous Solutions

In the previous blogpost, we have discussed on the 2nd criterion for predicting products of electrolysis for aqueous solutions under the Series on “Secrets of Redox and Electrolysis“.

Today we will end the series by introducing the 3rd criterion:

Consider: Nature of Electrodes Used in Electrolysis

Different products are discharged at the electrode when different type of electrodes are used.
When we say different types of electrodes used, it simply means:

Inert Electrode (such as Carbon and Platinum) vs Reactive Electrode (such as Cu or Silver)

We shall once again look at it in a step-by-step simplified approach.

Lets consider 2 electrolysis reactions using Copper(II) Sulphate as the electrolyte.

Set-Up A: Inert Electrodes such as Platinum

At the +ve Anode:

  • 4OH-(aq) –> 2H2O(l) + O2(g) + 4e-
  • SO42- ions remain in solution

At the –ve Cathode:

  • Cu2+(aq) + 2e- –> Cu(l)
  • H+ ions remain in solution

Summary:

  • Overall reaction is: 2CuSO4(aq) + 2H2O(l) –> 2Cu(s) + O2(g) + 2H2SO4(aq)
  • Acidic solution of H2SO4(aq) formed at end of reaction

Set-Up B: Reactive Electrodes such as Copper

At the +ve Anode:

  • Cu(s) –> Cu2+(aq) + 2e-
  • Anode dissolves to form Cu2+ ions in aqueous solution

At the –ve Cathode:

  • Cu2+(aq) + 2e- –> Cu(l)
  • H+ ions remain in solution
  • Cathode becomes coated with a layer of reddish-brown Cu

Summary:

  • Cu is transferred from the anode to the cathode
  • Cu cathode slowly increases in mass
  • Cu anode decreases in mass
  • Colour & Concentration of CuSO4 remain unchanged
  • No effective loss of Cu2+ ions from the CuSO4 solution

Let’s check out 1 question to see how much you understand.

Question:
Aqueous copper(II) sulphate is electrolyzed using copper electrodes. Which observations will be made?
Anode (+ve) Cathode (-ve) the electrolyte
A. anode dissolves           pink solid forms          blue colour fades
B. anode dissolves           pink solid forms           no change
C. colourless gas forms   colourless gas forms    no change
D. colourless gas forms   pink solid forms blue   colour fades

PS: Remember to leave down your answers in the “Leave A Reply” section below.

PPS: To learn everthing on Redox & Electrolysis, please visit the section right below called “Table of contents for Secrets of Redox & Electrolysis

Formulae 1 Singapore Grand Prix – A lesson towards GCE O Level Chemistry Exam

Over the weekend, we have seen some dramatic moments in Singapore’s frist ever Formulae 1 Singtel Singapore Grand Prix. There were plenty of thrills and spills.

We will look into some highlights and see how it is associated with students taking their O Level Chemistry exams in less than 3 weeks time.

Before last night, the drivers’ championship race was a tight race, with Ferrari’s Massa just a point behind leader Hamilton. Yesterday, on lap 18, Massa entered the pit as the race leader for 16 laps (he was leading the pack after starting at Pole Position – a 1st car line-up position he earned on Saturdays race). His crew’s signal that he could leave the pit came too early, and he drove off with a huge part of the refuelling rig still attached to his car.

With no other choice, he had to drive all the way to the end of the pitlane to clear the other nine teams’ garages (defending constructors’ race champions Ferrari’s garage is the first in the pits) before he could pull over. Massa could only sit helplessly for more than an agonising minute as Ferrari’s pit crew has to first serviced teammate Kimi Raikkonen’s car before sprinting roughly 250m to Massa’s and detach the hose. To make matters worse, Massa was hit with a drive-through penalty for pulling out dangerously close to another car, and he rejoined the race in 18th place.

Here is a lesson for students that had done really well in their Preliminary Examinations.

Do not get complacent even you have been getting A1s for Chemistry for Preliminary Exams or other previous qualifying exams. So many times, we have seen “smart” students crying when they only get a B for Chemistry when results for O Levels are released. You need to be focussed and consistent all the way before the finals.

Back to the race which was won by Renault’s Spanish driver Fernando Alonso. For former two-time drivers’ champion, this is his first win in over a year and was a sweet victory following a disastrous qualifying session on Saturday. He was fastest in the second and third practice sessions. But his engine failed halfway through qualifying and crashed out. On saturday, a frustrated Alonso threw his hands up in the air while leaving his car. He had the pace to contend for pole position, but instead start 15th out of 20 cars on the starting grid yesterday.

Many enthusiats have already written him off. But yesterday, after climbing out of his car after the race, Alonso raised his arms, this time in jubilation. Many written him off – but he has never given up hope, and kept chasing and performing, till he have the final smile on the track.

Here is a lesson for students that have failed in their Preliminary or other Qualifying Exams:

There is no such thing as absolute failure. In fact, there is no such thing as failure – there is only unsuccessful method learned and strategies used. Just get the right method and have the correct mindset, and you can be the eventual Winner. We have seen many cases where students that failed their Prelims – and came back to top their cohort or to score the As they wished for so long..

You won’t know the final outcome until the finish line. There is still 3 weeks for you to prepare for your O Level Chemistry Examination – enough time for you to pull up something remarkable like Alonso. Question is – Do you believe you can do it & whether You want to do it!

Until next time next blog-post, i wish you the best during your exam preparation.

PS: Drop me a comment or two, i would love to hear from you.

O Level Chemistry – Strategies to Predict Products of Electrolysis for Aqueuous Solutions

In the previous post, we have discussed on the 1st criterion for predicting the products of electrolysis for Aqueous Solutions, that is to determine the Position of Metals In The Reactivity Series.

Today, we are going to look at the 2nd criterion, that is:

Effect of Concentration of Solution on Effective Discharge

  • It applies only to ANIONS
  • Only for Concentrated Solutions
  • An increase in the concentration of an anion tends to promote its discharge

Example:

Consider Electrolysis of concentrated NaCl solution using carbon electrodes.
2 types of anions are attracted to the anode: Cl- and OH- ions

According to the reactivity series, OH- ions should be discharged preferentially (as we have seen in the previous post on diluted aqueous solutions). However, Cl- ions are far more numerous than OH- ions and so are discharged instead.

Try out this question to see if you understand this concept.

Question:

What would you observe when a concentrated solution of HCl is electrolyzed using Platinum electrode? Explain your observations and write down the equations involved.

PS: Remember to leave down your comments and suggested answers in the “Leave Your Reply” section below.

‘do your best for exams’ video for all my readers

Here is the video which takes alwaysLovely from singaporeolevelmaths.com about 45 minutes to create:

http://www.youtube.com/watch?v=ZyJL2z6xO2w

Click here to download of the slides in pdf format & send it to at least one other friends who is taking exams.

Melamine in Milk Powders – Chemistry put in Wrong Use

All (if not Many) of you should have heard about the Melamine Adulteration in milk powders made from china for the past 2 weeks. More common words you heard would perhaps be “Sanlu Milk causing deaths of babies“.

Since this is a chemistry blog-site that also discussed about Chemistry Phenomenons (besides sharing of Chemistry Tips & Strategies), we shall discuss a little bit of this Melamine Scare – a case of Chemistry put into Wrong Use.

Melamine is an organic compound with the chemical formula C3H6N6, with the IUPAC name 1,3,5-triazine-2,4,6-triamine, and is only slightly soluble in water. It is commonly used as a fire restardant in commercial products and china is the major supplier of melamine globally.

Ingestion of melamine may lead to reproductive damage, or bladder or kidney stones, which can lead to bladder cancer. In this recent case in China which gone public in september 2008, Sanlu recalled all powdered milk in China where melamine was reported to have been used in 22 brands of infant formula, making more than 50,000 infants ill and hospitalizing almost 12,900. Several have already died at the time of post. Melamine has also been found in products produced by a dozen more companies, including Mengniu, Yili, and Yashili, all now being internationally distributed (yes, we have all these in Singapore).

Melamine have been added to fool government quality tests after water was added to fraudulently increase the milk’s volume. The adulterant melamine was added to the milk to allow dilution of the milk with water and circumvent government regulations, since melamine will cause a false increase in the measurement of protein by increasing the Nitrogen levels in the milk (Milk must have high content of protein – which is shown by high content of Nitrogen).

Hope you learn something about this global concern where Chemistry is put into wrong use.

But before we end this post, i just have a chemistry-related question to ask you.
I have mentioned that these chinese milk-manufacturing companies had added Melamine to milk to increase the NITROGEN CONTENT.

Now, based on information in earlier part of this blog-post, can you:

Question: Calculate the % Mass of N in Melamine??

This will allow you to see why these unscrupulous business owners are using melamine to increase their profits.

PS: Leave your comments and/or answers in the “LEAVE ME A REPLY” section below. I would love to hear from you.

O Level Chemistry – How to Learn Quickly & Effectively

Everything around us is about ENERGY.

In physics, we learn about the Law of Conservation of Energy where Energy is never created or lost. Instead, Energy is transferred from one place to place, from one form to another.

Many of you asked me how come i am able to coach students to learn and like Chemistry so quickly and effectively, as seen in our Mastery Workshops and Intensive Bootcamps.

Today i am going to let out that secret – and that secret is “ENERGY“.

If you are a student and is preparing for your upcoming GCE O Level Chemistry Examinations in 24 days time..ask yourself…are you utilizing the correct energy level to revise your work…is this the same kind of energy level where you play computer games, play soccer or your shopping… That gives you a clue isnt it?

Perhaps, you will understand what i mean by taking sometime to watch this short video clip:

Alternatively, you can visit the url:

GCE ‘O’ Level Chemistry Final Leap Programme – Final Revision

To all students sitting for the GCE ‘O’ Level Chemistry Papers in 27 days time, all the best!

Click here for Chemistry Final Leap Programme

Over the last few months, we have helped students that wants to improve their Chemistry grades by conducting Programmes such as:

  • Small Group Essential Concepts Class
  • Chemistry Intensive Revision Bootcamps
  • Series of Chemistry Mastery Workshops

GCE ‘O’ Level Chemistry Exams will commence in 27 days time. Are you looking for a proven system to Improve Your Chemistry Grades exponentially in a short period? Yes. You can do that, but it requires your 100% Commitment, 150% Participation and 200% DESIRE TO SCORE LIKE A WINNER!

Here is what i have for committed students:

A Final Chemistry Revision Programme especially catered for Singapore students (Programme will be held in Singapore) who still have not scored what you deserved.

If you have failed your Chemistry Prelims or have never passed your Chemistry before despite many tuition classes or school lessons, this will be your last chance to score the marks you truly deserve.

Here’s what GCE ‘O’ Level Chemistry Final Leap Programme will do for you:

  • Equip you with the Essential Chemistry concepts using Accelerated Learning Techniques & Association Strategies so that you can understand better and retain more during this short period of time
  • Expose you to the Secrets of Lnking Concepts on examination questions so that you can Score!
  • Help you to Regain the Confidence required to fight the Chemistry examination victoriously
  • Shock you on how you can Score in Chemistry easily just by Applying Step-by-Step Strategies

All based on real GCE ‘O’ Level exam-based questions.

Here’s what I want you to do next:
Click here to tell me what you need to SCORE in your O Level Chemistry. Leave your contact details so that we can get in touch with you asap.

Click >> Testimonials from students

I do not care much how you fare for your Chemistry previously; I just need to know that you believe you want to do much better for NOW!

Tell me What you need to SCORE in Chemistry?

PS: Priorities will be given to students that have never passed their Chemistry exam before.

PPS: This will be a 1-to-1 customized coaching by myself, i can only accept 1-2 students

PPS: Non-local students – my sincere apology not able to coach you personally. Visit this blog-site for more tips