Mole Calculation Mastery Workskop

Hi Students,

2 months to GCE O Level, Have you scored the marks you truly deserved?

Is Mole Calculations your #1 Killer Topic?

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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 formulaes to use…WHY?

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Let’s check out a typical exam question on Mole Calculations:

Question:

The following equation represents the precipitation reaction between lead (II) nitrate solution and potassium iodide solution.

aPb(NO3)2(aq) + bKI(aq) –> cPbI2(s) + dKNO3(aq)

In an experiment, 20.0g of lead(II) nitrate and 20.0g of potassium iodide were dissolved separately to form 250cm3 of lead (II) nitrate solution and 250cm3 of potassium iodide solution.

(a) Determine a, b, c and d. (2 marks)

(b) Using suitable calculation, identify the limiting reactant. (2 marks)

(c) What is the maximum mass of lead (II) iodide (PbI2) that can be obtained from the experiment? (2 marks)

(d) What is the concentration of potassium nitrate in the reaction mixture when the reaction is completed? Give your answers in mol/dm3. (2 marks)

(e) Write an Ionic Equation for the above reaction and identify the spectator ion. (2 marks)

Here is the answers:

a) a = 1 , b = 2, c = 1 and d = 2

b) KI is the Limiting Reactant.

c) Maximum mass of PbI2 that can be obtained = 27.8g (to 3 sf)

d) Concentration of KNO3 = 0.241 mol/dm3

e) Ionic Equation: Pb2+(aq) + 2I-(aq) à PbI2(s). Spectator Ions: NO3-(aq) and K+(aq)

PS: If you cant solve those questions comfortably, i strongly encourage to join us at the Mole Calculations Mastery WOrkshop on 16th Aug, where you know everything that you need for Mole Concepts, before your nearing Exams.

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Happy 43rd National Day Singapore!

Lyrics :

Have you seen a star,
One that guides you no matter where you are?
However vast the sky may be
Or dark it seems
You can be sure, it's always there for you and me

Have you heard a song,
One that moved you, one that made you sing along?
Your dreams and hopes will all come true
If you believe that every vision begins with you.

Shine for Singapore
This is your song
Deep inside your heart where it belongs
It'll always stay, strive for your goals.
You will achieve with visions so bold.

Shine for Singapore
This is our song
Reach out for the sky, far and beyond
As one we'll stand, we're Singapore
It's here that we belong

Have you heard a song,
One that moved you, one that made you sing along?
Your dreams and hopes will all come true
If you believe that every vision begins with you.

Shine for Singapore
This is your song
Deep inside your heart where it belongs
It'll always stay, strive for your goals.
You will achieve with visions so bold.

Shine for Singapore
This is our song
Reach out for the sky, far and beyond
As one we'll stand, we're Singapore
It's here that we belong

Nowhere i'd rather be, this is home to me
This star shines strong and free