O-Level Chemistry Made Easy

In the previous blogpost, i have introduced to you the Periodic Table which is a table that Chemists used to help them organise information. The Periodic Table is useful to Chemists because it can be used to predict the properties of an element based on its position in the Table.

In the YouTube video below, i will discuss on the Group VII Elements (commonly known as the Halogens) in terms of their Physical & Chemical Properties. I will also highlight to you what are the possible questions that examiners like to ask in Chemistry examinations.

Direct link to video: http://youtu.be/jChTEHAvrBg

Note: Colour of Iodine Solids is commonly stated to be Purplish-Black (in the video i mentioned it is Black in colour)

Hope you learned something important to UP your Chemistry grades and interests. Do try out the question that was posted at the end of the video. You can leave your comments/solutions in the Comments Section below. Adding a balanced chemical equation for that Halogen Displacement Reaction would show that you are cool!

If you think the concepts discussed are useful to your friends, feel free to forward this blog post to them.

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(Image by microwavedboy)

It is important that O-Level Chemistry students understand the concepts about Isotopes in order to answer application questions related to it.

Isotopes are atoms of the same element with the same number of protons but different number of neutrons.

This mean that for isotopes, the number of protons and electrons will be the same but the mass (nucleon) number will be different.

Take chlorine as an example. 75% of naturally chlorine atoms are Cl-35 and the remaining being Cl-37. By simple math, you should get the average atomic mass (A_r) of chlorine to be 35.5 as shown in most Periodic Table.

Click HERE for more in-depth discussions on Isotopes in the topic of Atomic Structure.

Most elements in the periodic table have isotopes, and many of these isotopes are radioactive. Some of the common uses of radioactive isotopes are in medical & chemical industry. Clean energy industry such as the Nuclear Plants are making use of the radioactive isotopes to produce large amount of energy in several countries, much to the disapproval by groups that are aware of the danger in radioactive substance.

Let’s take a look at a very common exam-based Multiple Choice Question (MCQ).

Quick Check 1:

Isotopes are

A)  atoms of the same element with different masses

B)  atoms of different elements with different masses

C)  atoms of different elements with the same mass

D)  atoms of the same element with same mass

Based on our discussion, we should arrived at answer A with two sets of keywords “atoms of the same element” and “different masses”.

Now, try out the following MCQ question on your own:

Quick Check 2:

Which of the following statements concerning the two isotopes 146C and 147N is/are correct?

1. Both isotopes have the same chemical properties

2. Both isotopes contain 14 nucleons per atom

3. The carbon isotope has more neutrons per atom than the nitrogen isotope

A)  1, 2 and 3 are correct

B) 1 and 2 only are correct

C) 2 and 3 only are correct

D) 3 only is correct

Go try it out and leave your thoughts/answers in the comment section below. Do participate in the discussions to help each other to master Chemistry.

PS: If you find this post on Isotopes useful to any of your friends, feel free to forward to them. =) Keep sharing!

This question is about Preparation of Salts that was sent to me by one of my Sec 4 Pure Chemistry student.

Before we take a look at the question, let’s recap that there are 3 main methods to prepare salts in the laboratory:

1. Titration
2. Acids + Excess Insoluble Substances
3. Precipitation

If you need more information on Preparation of Salts, you can go to my earlier blogposts under archives.

Let’s take a look at the question.

Question:

A student was given two beakers, one containing an aqueous solution of sodium chloride and the other aqueous lead (II) nitrate. He was told to prepare lead (II) chloride using those reagents.

(i) What is the name of the method that he used to prepare the salt?

(ii) Name the other  product made, besides lead (II) chloride

(iii) Write an ionic equation for the preparation.

In the process of doing the experiment, he accidentally spilled some of the salt solutions. Since he could not obtain sufficient lead (II) chloride, he tried to prepare more lead (II) chloride by adding solid lead (II) carbonate to dilute hydrochloric acid. Effervescence was seen but the reaction stopped in a short while.

(iv) Why was there effervescence?

(v) Why was he unsuccessful in preparing lead (II) chloride from the process of adding dilute hydrochloric acid to lead (II) carbonate?

Go try it out and leave your answers (and workings) in the Comment Section below.

PS: Feel free to share this blogpost with your friends or classmates, if you think they will benefit from it

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