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During the O Level Chemistry Essential Concepts Revision Workshop, i had observed that many of the participants will make common mistakes in certain types of questions. It is not 1-2 students, but more than 50% of them will make these common mistakes. Many of these questions are in fact discussed and presented in my chemistry book “Up Your Chemistry Grades Now!”.

For the next 1 week, i will blogpost about some of the common errors that are made by these group of revision workshop participants, so that everyone is aware of it, and can avoid it in Chemistry Exams. This mini series will be known as “Common Errors in Chemistry Concepts made by Students”.

Check out the question below for the 1st misconceptions that many students made:

Question:

Explain the following observation:

“Solid sodium chloride does not conduct an electric current but a solution of sodium chloride in water is a good conductor.” (2 marks)

Common Mistake made by students:

“Sodium chloride in solid state cannot conduct electricity but when they are dissolve in water, there are free moving electrons that can carry charges and thus conduct electricity.” – student’s answer

Comments on the common mistakes made:

Many students made the mistake by mentioning that sodium chloride conducts electricity when they are dissolved in water, because there are free moving electrons. They must have learned that electricity flows due to free moving electrons in wires/circuits.

This is NOT true for ionic compounds such as sodium chloride.

Ionic compounds conducts electricity when they are in aqueous state (dissolved in water), because of the FREE MOVING IONS, not electrons.

Water molecules are able to overcome the strong electrostatic forces of attraction between the positive and negative ions, such that the ions are free moving and can carry charges around.

Hope this explanation is clear to you.

Drop me a comment on how you find this blogpost discussion.

PS: More of such “Common Mistakes Made by Students in Chemistry Exams” are documented in “Up Your Chemistry Grades Now!” chemistry guidebook.

Related Articles:

• O Level Chemistry Essential Concepts Revision Workshop – Post Analysis Series – Part 3
• Chemistry Examination Tips – Paper 2
• O Level Chemistry Questions – Qualitative Analysis (QA) / SPA Tips
• O Level Chemistry – Definitions of Electrolysis
• O Level Chemistry: Ionic Bonding