Category Archives: Chemistry Notes & Tips

Chemistry Phenomenon: Nitrogen Dioxide as an Air Pollutant

Being a Chemistry Trainer and also a fellow cyclists (yes guys, i love to cycle), i read this local Straits Times Newspaper article with interest.

Seems like our Nitrogen Dioxide, NO2(g) level within the lower atmosphere level is quite high in Singapore.

NO2(g) is considered a major air pollutant which has the following harmful effects:

1) eye and lungs irritation and causes breathing difficulties

At high levels, it may even lead to inflammation of the lungs i.e. bronchitis

2) acid rain consisting of Nitric Acid HNO3 that is highly corrosive

In the presence of oxygen in the air, nitrogen dioxide is converted to nitric acid via the following chemical equation:

4NO2(g) + 2H2O(l) + O2(g)  4HNO3(aq)

Nitric acid corrodes buildings and harms aquatic life and plants.

Do you know that due to acid rain, the Statue of Liberty in the United States of America had been badly corroded. In the year of 1983, the US Government launched a campaign to restore this historical figure of US? Chemistry in action indeed!

NO2(g) is formed due to 2 main sources:

1) Lightning activities (which we have no control over since it is a natural source and it is NOT a daily source)

2) Vehicle exhaust fumes where high temperature around vehicles engine (which is a man-made source) causes 21% O2(g) and 78% N2(g) in the air to react to form oxides of nitrogen, NOx(g) which is mainly nitrogen monoxide, NO(g) and nitrogen dioxide, NO2(g).

Nitrogen reacts with oxygen at high temperature to form nitrogen monoxide or nitric oxide, NO(g).

N2(g) + O2(g)  2NO(g)

Nitrogen monoxide reacts with oxygen to form a brown colour gas called nitrogen dioxide, NO2(g).

2NO(g) + O2(g)  2NO2(g)

From the article, it shows that as concentration of air particulates (unburnt hydrocarbons) increases due to incomplete combustion of fossil fuels in vehicle exhaust fumes, there is also an increase in the concentration of nitrogen dioxide, NO2(g).

Since the satellites images have shown that the recent haze in Singapore is not from Indonesian fires (slash and burn method), it should be from the amounts of vehicle exhaust fumes produced locally on a daily basis.

  • More vehicles running on the roads
  • More incomplete combustion of fossil fuels
  • More unburnt hydrocarbons being produced
  • More nitrogen dioxide is also being produced
  • As such, the amount of unburnt hydrocarbons and the amount of nitrogen dioxides are highly correlated in a city which has a large number of vehicles running on the ground.

Time to ponder about if Singapore should encourage less driving….for our health and environment.

This is a good case study for GCE O-Level Pure Chemistry and Combine Science Chemistry students in Singapore to put their concepts learned in school into actual practice and application.

Same applies to Chemistry students worldwide doing other syllabus. This can be particularly severe in large cities, where traffic is heavy.

I hope you find the content easy for your understanding and if you have any questions, leave me a comment below.

Subscribe to my blog to receive 2 updates per month sent to your email!

Feel free to share this blog post with your friends who needs help in mastering Chemistry.

#Haze #HazeInSingapore #ChemistryConcepts #ChemistryPhenomenon #OLevelChemistry #PureChemistry #ChemistryInAction #Chemistry #EverydayChemistry #Geography #AirPollution #AirAndAtmosphere

O-Level Chemistry Question: Periodic Table & Group Trends

I received an email from Mahrukh, one of the reader of SimpleChemConcepts.com. She is a Chemistry student and asked me about an examination question regards to the topic of Periodic Table & Group Trends.

I have decided to take this opportunity to discuss this question by her with a blog post today so that more students can benefit from it.

Her question as follows:

Question:

Sulfur and selenium, Se, are in the same group of the Periodic Table. From this, we would expect selenium to form compounds having the formulae

A) Se2O, Na2Se and NaSeO4

B) SeO2, Na2Se and NaSeO4

C) SeO2, Na2Se and Na2SeO4

D) SeO3, NaSe and NaSeO4

Regarding your question, this should be covered under “Periodic Table & Group Trends” in most Chemistry Syllabus in different countries.

The concept that she is being asked is known as “Same Group Properties“.

Elements in the same Group of the Periodic Table will have the same number of valence or outermost shell electrons.

As such, elements in the same Group of the Periodic Table would tend to form compounds with similar chemical formula.

Sulfur is a Group VI element and has 6 valence electrons.

  • It forms SO2 – so we expect SeO2 to exist.
  • It forms Na2S – so we expect Na2Se to exist.
  • It forms Na2SO4 – so we expect Na2SeO4 to exist.
  • As such, the answer will be option (C).

    Hope the above explanation is useful to you.

    PS: If you are not sure why we have the following chemical formulae (SO2, Na2S, Na2SO4)  in the first place, you can revise via this blog post on Writing Chemical Formulae of Ionic Compounds and Covalent Substances.

    Subscribe to my blog to receive 2 updates per month sent to your email!

    Feel free to share these videos with your friends who needs help in mastering Chemistry.

    O-Level Chemistry: Strength versus Concentration of Acids

    In the previous blog post, we have watched a video on the difference between Strength of Acids and Basicity of Acids.

    If you have missed it, you can click HERE to watch it.

    Today, we are going to discuss another misconception by many students studying basic Chemistry.

    It is very important not to confuse the Strength of Acids with the Concentration of Acids.

    I have observed that many of my GCE O-Level and IGCSE Sec 3 and Sec 4 Pure Chemistry Tuition Class students are confused by what they have learned from their school’s Chemistry teachers or previous home-based Chemistry tutors. It usually take me some effort to re-align their concepts and associated keywords.

    As we have learned in the previous blog post, Strength of Acids refers to the extent of dissociation (or ionisation) of an acid. We will see words like “STRONG” and “WEAK“.

    Concentration of Acids is different. It refers to how much of an acid (the solute) is dissolved in the solution. We will see words like “CONCENTRATED” and “DILUTE“.

    Note that the strength of an acid is not affected by its concentration.

    A dilute acid solution is not the same as a weak acid solution, and a concentrated acid solution is not the same as a strong acid solution.

    i.e Dilute Acid  Weak Acid

    i.e Concentrated Acid  Strong Acid

    A strong acid will dissociate completely regardless of its concentration (whether it’s dilute or concentrated).

    A weak acid will dissociate partially regardless of its concentration (whether it’s dilute or concentrated).

    The term concentration is actually a concept covered in the topic of Mole Concepts or Mole Calculations.

    The concentration of a solution is given by the amount of a solute dissolved in a unit volume of the solution.

    Recall that a solution is made up of a solute and a solvent i.e. Solution  Solute + Solvent

    As such, concentration of an acid can be easily changed!

    You can decrease the concentration of an acid solution by adding more solvent to it.

    You can also increase the concentration of an acid solution by adding more solute to it.

    However, the strength of an acid cannot be changed!

    A strong acid like HC(aq) will always dissociate completely to produce a high concentration of hydrogen, H+ ions, regardless of whether the solution is dilute or concentrated.

    A weak acid like CH3COOH(aq) will always dissociate partially to produce a low concentration of hydrogen, H+ ions, regardless of whether the solution is dilute or concentrated.

    Hope the above explanation is clear to you.

    Together with the previous blog post, i have discussed on the difference between these three common terminologies used in the topic of Acids and Bases, namely:

    Strength of Acids  Basicity of Acids  Concentration of Acids

    I hope you find the content easy for your understanding and if you have any questions, leave me a comment below.

    Feel free to share this blog post with your friends who needs help in mastering Chemistry.

    PS: You can do a search on the top right hand corner for more discussions and questions on “Acids and Bases” or select from the suggested blog posts under “Related Articles” below.

    PPS: If you are based in Singapore and want to master Acids, Bases and Preparation Salts, i will be conducting an annual Topical Chemistry Revision Workshops during the June School Holidays. You can get in touch with us at PassWithDistinction.com to find out more.