In Mole Calculations, many students lose marks in questions related to Volumetric Analysis, especially on those that requires them to understand the concepts of CONCENTRATIONS of solutions. Volumetric Analysis are always a highlight in our annual Mole Calculations Mastery Workshop.

Concentrations of a solution refers to the amount of solute dissolved in 1 dm3 of the solution.

Do note that

Solution = Solute (minor component) + Solvent (major component)

Usually in basic chemistry such as O Levels, the solvent used is Water. As such, the solution formed is usually aqueous solutions whereby certain solid or liquid are dissolved in water.

Concentrations can be expressed in:

• Grams of solute per dm3 (unit will be g/dm3)
• Moles of solute per dm3 (unit will be mol/dm3)

The most important formulae student need to know in volumetric analysis are:

Conc. (mol/dm3)  = Amt. of Solute (mol) / Vol. of Solution (dm3)

&

Conc. (g/dm3)  = Amt. of Solute (g) / Vol. of Solution (dm3)

Let’s check out a question to see how we can use the formulae above.

Question:

60g of NaOH is dissolved in water and make up to the total volume of 500cm3. Calculate the concentration of solution in i) g/dm3 and ii) mol/dm3.

Answer:

i)

Mass of NaOH = 60g

Volume of solution in dm3 = 500/1000 = 0.5dm3

Concentration of solution in g/dm3 = 60 g /0.5 dm3 = 120 g/dm3

ii)

Mr, Relative molecular mass of NaOH = 23 + 16 + 1 = 40

Moles of NaOH = Mass / Mr = 60/40 = 1.5 mol

Concentration of solution in mol/dm3 = 1.5 mol / 0.5 dm3 = 3 mol/dm3

Isn’t it easy if you know the strategy of doing it? I would love to hear from you. Leave me a comment.

For those itching to try out a question on your own. Check out the Quick Check below with a little bit of twist.

Quick Check 1:

Given concentration of a NaOH solution is 1.5 mol/dm3. How many moles of NaOH are contained in 2.0 dm3 of solution?

PS: Try it out and leave your suggested answer (working even better) below!

As you can see from the on-going survey on the right hand side, Mole Calculations (commonly known as Mole Concepts) has been voted by students as the #1 Killer Topic in O Level Chemistry (and other equivalent basic Chemistry Syllabus).

In fact, a large number of students skip the calculation-based questions when they see it on Chemistry examination, fearing that they spend alot of time on that question, and yet could not answer it.

Over the years, this topic is often voted the “Hot Favorite” on students’ challenging topics. Some:

• have problems understanding what the question is asking for
• do not know where to start
• totally blank when they read the question
• too confused with the formulae to use
• gave up on Mole Calculations totally

Many a times, question will require you to write a Balance Chemical Equation in order to solve the question. Other times, they will also require you to write the Ionic Equation and state the Spectator Ion.
As such you will need the following basic foundations that i have shared some time ago:

4 Steps-Process to write a Balanced Chemical Equation

7 Steps-Strategy to write the Ionic Equation & Spectator Ion

The best way to learn is NOT TO READ, but to DO IT!

Let’s try out one exam-based question(similar to O Level Chemistry Exams):

Question 1:

Copper (II) oxide reacts with dilute sulfuric acid to produce a salt, copper (II) sulfate and water. This process is known as Neutralisation.
i)  Write a balanced chemical equation with state symbols
ii) Write the ionic equation and state the spectator ion of this reaction

PS: Try it out and leave your answers below.

Quick Announcement for Singapore Readers:

Extension to Early Bird Price Registration for Mole Calculations Mastery Workshop 2010

We received a handful of requests for us to extend the bird early registration for the workshop as many schools in Singapore have yet to announce their March Holidays schedule.

We hear you and would want to help committed students to join us at this important (Number 1 killer topics for Chemistry) revision workshop at the special early bird workshop fee.

After much discussion, we have made the decision to extend the early bird registration to 10 March 2010 for all our March Holidays workshop.

Click here for the registration:
http://www.SimpleChemConcepts.com/molecalculations/early-bird.html?r=1

However, do note that we will close registration early once all seats are taken.

We look forward in meeting your child at the workshop!

Cheers to your academic success,
Sean

PS: I was informed that there are only 5 4 seats left. Act now!
http://www.SimpleChemConcepts.com/molecalculations/early-bird.html?r=2

PPS: Want to ace your E-Math? Circles Mastery Workshop is available during March Holidays also. Click on this link to find out more: http://www.singaporeolevelmaths.com/emath-circles.html

Do you find Mole Calculations difficult?

Mole Calculations, or commonly known as “The MOLE” or “Mole Concepts” is regarded by many of the GCE ‘O’ Level Chemistry students (as well as IGCSE and IB / IP Chemistry students) to be one of the most challenging and difficult topic.

Let’s not mention that many students are not able to score in this topic!

In fact, a large number of chemistry students simply “hate” Mole Calculations, because they:

• Don’t know which formulae to use
• Don’t even know how to start when they read the question
• Can’t relate how mathematical manipulations are connected to chemistry theories
• Can’t handle the fact the Mole Calculations are everywhere & anywhere in Chemistry Exams – they appear in questions that are linked to various other chemistry topics

As such, many students have in fact given up on Mole Calculations! But question is: Can they afford to give them up? Let me know your views on it? Do you think students can afford ignore Mole Calculations?

Even worst, we have received emails from chemistry teachers and chemistry tutors (tuition centre teachers) on the challenges in teaching their students. Many students seemed to “understand” the examples shared by their chemistry teachers during lecture but once the question is rephrased a little bit, students will be stunned and do not know how to carry on. Are you one of them? I would love to hear from you.

Recently, we have seen more students asking us to discuss more about Mole Calculations in this chemistry blogsite. One of my chemistry student, who is committed to do well in the October’s GCE ‘O’ Levels Chemistry Exams, had sent me a series of questions related to Mole Calculations. And one of them is a challenging application question that i have addressed last year (2009). Let’s check out the question:

Question:
12dm3 of polluted air is passed through limewater so that all the carbon dioxide is precipitated as calcium carbonate. The mass of calcium carbonate formed is 0.05g. What is the percentage by volume, of carbon dioxide in the air sample?

Now, take out your calculator, pen & paper – and try it out! Leave your answer (and even better, leave down your working) in the Comment section below.

I will be providing the solution soon. But before that, i would strongly suggest that you attempt the question first to see if you have the correct answer. =)

Suggested Solution:
Updated on 2nd March 2010:

For full screen video – click HERE

PS: If you are based in Singapore, there is a chance now that you can master Mole Calculations quickly & effectively. Click HERE for more information.

Mole Calculations has been voted as #1 Killer Topic for ‘O’ Level Chemistry

Click on the PLAY button (2 mins audio) to find out why!

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>> Click HERE for Early Bird Registration to enjoy discounts & bonuses

>> Click HERE for Early Bird Registration to enjoy discounts & bonuses

Here is a question sent in via email by an avid student reader of this chemistry blogsite.

Hope to see some suggested answers below and the reasoning/explanation to it.

PS: Remember – Do not be afraid of making mistakes now. I rather you make mistakes now then during your examinations.

Question 1:

20cm3 of a gaseous hydrocarbon was mixed with 100cm3 of oxygen and the mixture sparked so that the hydrocarbon was completely burnt. The volume of gas remaining at the end of the combustion was 70cm3. After passing over soda lime, this volume was reduced to 10cm3. All gases were measured at 25C and at the same pressure.

(a) What volume of oxygen gas remained unburnt at the end?
(b) What volume of oxygen gas was used in the combustion?
(c) What volume of carbon dioxide was produced in the combustion?
(d) Deduce the formula of hydrocarbon.

All (if not Many) of you should have heard about the Melamine Adulteration in milk powders made from china for the past 2 weeks. More common words you heard would perhaps be “Sanlu Milk causing deaths of babies“.

Since this is a chemistry blog-site that also discussed about Chemistry Phenomenons (besides sharing of Chemistry Tips & Strategies), we shall discuss a little bit of this Melamine Scare – a case of Chemistry put into Wrong Use.

Melamine is an organic compound with the chemical formula C3H6N6, with the IUPAC name 1,3,5-triazine-2,4,6-triamine, and is only slightly soluble in water. It is commonly used as a fire restardant in commercial products and china is the major supplier of melamine globally.

Ingestion of melamine may lead to reproductive damage, or bladder or kidney stones, which can lead to bladder cancer. In this recent case in China which gone public in september 2008, Sanlu recalled all powdered milk in China where melamine was reported to have been used in 22 brands of infant formula, making more than 50,000 infants ill and hospitalizing almost 12,900. Several have already died at the time of post. Melamine has also been found in products produced by a dozen more companies, including Mengniu, Yili, and Yashili, all now being internationally distributed (yes, we have all these in Singapore).

Melamine have been added to fool government quality tests after water was added to fraudulently increase the milk’s volume. The adulterant melamine was added to the milk to allow dilution of the milk with water and circumvent government regulations, since melamine will cause a false increase in the measurement of protein by increasing the Nitrogen levels in the milk (Milk must have high content of protein – which is shown by high content of Nitrogen).

Hope you learn something about this global concern where Chemistry is put into wrong use.

But before we end this post, i just have a chemistry-related question to ask you.
I have mentioned that these chinese milk-manufacturing companies had added Melamine to milk to increase the NITROGEN CONTENT.

Now, based on information in earlier part of this blog-post, can you:

Question: Calculate the % Mass of N in Melamine??

This will allow you to see why these unscrupulous business owners are using melamine to increase their profits.

PS: Leave your comments and/or answers in the “LEAVE ME A REPLY” section below. I would love to hear from you.