Saturday, June 6, 2009

Chemistry - Chemical Calculations (Part 1)



The chemistry question is,


Sodium Carbonate flakes: Picture is extracted from http://www.earlham.edu/chemicalhygiene/images/Sodium%20Carbonate%20Snowflake_bw_web.jpg



Sodium Carbonate Structure: Picture is extracted from http://upload.wikimedia.org/wikipedia/commons/2/2d/Sodium-carbonate-xtal-Na-coordination-3D-balls.png

Solution:
(a)


That is, Mass of sodium carbonate
= 0.125 x [(23 x 2) + (12) + (16 x 3)]
= 0.125 x 106
= 13.25g (Answer)



Picture is extracted from http://www.fmcforet.com/Portals/Foret/Content/Images/Products/Silicates/Silicato%20solido.jpg
Solid Sodium Silicate an amorphous glass obtained through a process of direct fusion using silica sand and sodium carbonate



(b)




Sodium Carbonate flakes: Picture is extracted from http://www.dkimages.com/discover/previews/816/50024025.JPG


From the following formula






We have,
Number of moles of Solute = Concentration x Volume of Solution
That is, Number of moles of sodium carbonate
= 0.25 x 0.025
= 0.00625 mol


Sodium Carbonate Structure: Picture is extracted from http://www.chm.bris.ac.uk/webprojects2001/anderson/gifs/e500i.gif


From the Equation,


1 mole of sodium carbonate is completely neutralised with 2 moles of dilute hydrochloric acid
Therefore, 0.00625 moles of sodium carbonate requires 2 x 0.00625 = 0.0125 moles of dilute hydrochloric acid (answer).


It is drizzling again - 又是细雨 (yòu shì xì yǔ)

Reference
  • CHEMISTRY Matters (G.C.E. ‘O’ Level), 3rd Impression (2008), by Tan Yin Toon, Chen Ling Kwong, John Sadler, Emily, Published by Marshall Cavendish Education, Printed in Singapore by Times Printers, www.timesprinters.com, Chapter 9 – “The Moles”, Page 134 and Chapter 10 - “Chemical Calculations”, Page 150
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