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.

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With GCE O Levels Chemistry (Pure) and Combine Science Examinations in about 37 days time, i hope you are siphoning out some quality time to revise on your Chemistry Concepts.

In view that you might be looking for more questions to attempt, you can try out this question that was sent to me by my student from Cedar Girls.

Question:

Phosphorus and nitrogen are both in Group V of the Periodic Table.
Which ions are produced when phosphine, PH₃, dissolves in water?

A) PH₃⁺, H⁺

B) PH₄⁺, H⁺

C) PH₃⁺, OH^-

D) PH₄⁺, OH^-

Go try it out and leave your suggested answer and thought-process below.

PS: Feel free to send it to your friend that might benefit from this post.

PPS: Remember that mastery of Chemistry requires you to understand the key concepts and the ability to use it for application questions. Rote memorisation alone will not help you to achieve the grades you desire. You have 37 days more! Do something!

For all students learning O Levels Chemistry (and other equivalents), it is important that you understand the difference between the 3 types of formula commonly used – namely Molecular Formula, Empirical Formula and Structural Formula.

Previously, we have discussed on this topic before. You can find them HERE.

Let’s define them now, for better understanding and application:

Molecular Formula

- shows the exact number of atoms of each element in a molecule

Empirical Formula

- shows the types of elements (as well as the simplest ration of different types of atoms) in the compound

- commonly known as the Simplest Formula

Structural Formula

- shows the covalent bonds involved (single, double or triple covalent bonds) between each atom in the compound

- more for Covalent Molecules

Let’s look at some examples to look at the difference between Molecular Formula and Empirical Formula: