Mole Concepts | SimpleChemConcepts

Tag Archive: Mole Concepts

O Level Chemistry: Mole Calculations / Preparation of Salts

Written on October 12, 2010 by sean in Announcement, Chemistry Notes & Tips

O-Levels Pure Chemistry and Combine Science students in Singapore:

Hope you are revising well for your upcoming Chemistry Exam in 17 days time.

If you are looking for a programme to assist you to UP Your Chemistry Grades in such short time, we have one last workshop for you. Click Score 100% MCQ Mastery Workshop for details! Understand there are only 5 4 seats left!

For the last 2 weeks, i have been receiving many emails on questions related to Mole Calculations…many are based on the past years papers by University of Cambridge Local Examinations Syndicate (UCLES) and the Ministry of Education, Singapore (MOE).

I understand that many of you in Singapore are not satisfied puzzled with the answers provided by the Ten Years Series (TYS) booklet available in major bookstores, and the frustration as you prepare for exams. [2011 O-Levels students - i have something for you next year! You will going to love it! Subscribe to this blog and stay tuned!]

Back to 2010 O-Levels students,

I will not be able to discuss the ACTUAL O-Level question here due to copyright matters. Instead, i will try my best to share SIMILAR (but NOT IDENTICAL) questions and invite discussions.

Let’s try out this Mole Calculation’s question:

Question 1:

It was found that 10 cm³ of a 0.05 mol/dm³ solution of the chloride of a metal, X, needed 10 cm³ of a 0.1 mol/dm³ silver nitrate solution for complete reaction. What is the formula of the chloride?

A. X₂Cl

B. XCl

C. XCl₂

D. XCl₃

Try it first on your own! Once you have an answer, find out the Thought Process and my Suggested Solution by clicking the link below.

Enjoy!

3 Comments - Leave your comment!

O Level Chemistry: Molecular & Empirical Formulae

Written on August 31, 2010 by sean in Chemistry Notes & Tips

18 Comments

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:

18 Comments - Leave your comment!

O Level Chemistry: Mole Calculation Question & Common Mistakes Made

Written on August 22, 2010 by sean in Chemistry Notes & Tips

8 Comments

The following Mole Calculation question is not difficult but many O Levels Chemistry students tends to make mistake in exams, where time is not a luxury. When the same question was posed to my regular classes of Sec 3 and 4 O Levels and IP students, i realised that many fall into the trap also.

Let’s take a look at the question.

Question:

The relative atomic mass of chlorine is 35.5. What is the mass of 2 mol of chlorine gas?

A. 142g

B. 71g

C. 35.5g

D. 2g

Before we continue, let’s do a quick recap on the formula we need to use to solve this question, which is:

Mass = Mole x Mr of Molecule

Try it first on your own! Once you have an answer, find out the Correct Answer, Common Mistakes made by Students as well as my Suggested Solution below.

Enjoy!

8 Comments - Leave your comment!

O Level Chemistry: Challenging Mole Calculation / Electrolysis Questions

Written on August 14, 2010 by sean in Chemistry Notes & Tips

7 Comments

In the previous post, we have discussed on a MCQ question on Electrolysis that requires students to:

1. Write out discharge half equations

2. Do Molar Ratio Comparisons

Question:

Which of the following requires the least number of eletrons for discharge?

A. 2 mol of Al³⁺ (aluminium) ions

B. 5 mole of OH^- (hydroxides) ions

C. 3 mol of O^2- (oxides) ions

D. 6 mol of H⁺ (hydrogen) ions

Write your Answer and Suggested Working in the “Leave A Reply” section below.

PS: If you are not sure how to proceed, you can refer to the previous blogpost by clicking HERE

7 Comments - Leave your comment!

O Level Chemistry: Challenging Mole Calculation / Electrolysis Questions

Written on August 12, 2010 by sean in Chemistry Notes & Tips

4 Comments

In the previous post, we have discussed on 1 MCQ question on Electrolysis that requires basic Mole Calculations strategy to solve.

Do note that Electrolysis topic is only applicable to students taking:

GCE ”O” Level Pure Chemistry (Code: 5072)
Integrated Programme (IP) – it will be classified under Electrochemistry chapter
IB programme
IGCSE and other equivalents

It is NOT applicable to GCE ”O” Level students taking Combine Science syllabus.

Today, we shall continue to look into another challenging Electrolysis question.

Question:

Which of the following gives the largest number of eletrons for discharge?

A. 4 mol of Al³⁺ (aluminium) ions

B. 5 mole of OH^- (hydroxides) ions

C. 4 mol of O^2- (oxides) ions

D. 10 mol of Na⁺ (sodium) ions

Try it out! Once you have an answer, proceed to click the link below to see if you have gotten the correct answer. Suggested answer and thought process is given also.

4 Comments - Leave your comment!

O Level Chemistry: Challenging Mole Calculation / Electrolysis Questions

Written on August 11, 2010 by sean in Chemistry Notes & Tips

5 Comments

A few students from my weekly chemistry sec 4 classes have been asking me about the following Multiple Choice Questions (MCQ) on Electrolysis, more specifically on Electrolytic Cell.

It seemed like many secondary schools in Singapore had set this question in the recent school’s O Levels Preliminary Exams.

Question:

In an electrolysis experiment, the same quantity of electricity deposited 16g of copper and 6g of titanium.

What was the charge on the titanium ion?

A. 1+

B. 2+

C. 3+

D. 4+

What do you think?

Clue: Although this is question is on Electrolysis, you need to realise that it is calculation-based and you should be thinking of Mole Calculations at the same time.

Work it out on your own, before you click the link below to check the answer and my suggested solution (with thought process).

5 Comments - Leave your comment!

Chemistry Phenomenon: Thermit Process to weld steel railway lines together

Written on May 11, 2010 by sean in Chemistry Notes & Tips, Chemistry Phenomenon

2 Comments

Thermit Process_Welding of Railway Lines (Photo credit Ingy The Wingy)

Besides sharing Chemistry Tips and Exam Strategies, the other aim of this chemistry blogsite is to encourage students to learn the Chemistry Theories and Concepts in a more experiential and interesting way – HOW ? By relating chemistry theories to everyday life processes and experience.

Thermit Process came to my mind several days back when i was passing by the railway track in the west area of Singapore, and today i am going to share with you more on how Thermit Process – which is a highly exothermic reaction is used to weld together steel railway lines. It involves the reduction of iron (III) oxide to iron by aluminium.

Now, let’s check out a chemistry question that requires your concepts in several chemistry topics, namely:

Energy Changes (Endothermic/Exothermic Reactions)
Redox (Oxidation/Reduction)
Mole Calculations

Question:

In the highly exothermic Thermit Process to weld railway lines, aluminium is used to reduce iron (III) oxide to iron based on the balanced chemical equation below:

2Al + Fe₂O₃ -> Al₂O₃ + 2Fe

(a) Indicate the state symbols for all the reactants and products involved

(b) Calculate what mass of aluminium is needed to react completely with

2 Comments - Leave your comment!