Chemistry, Again, Homework Help.

Well, we were on hiatus.

I will give you some idea on how to design an experiment to determine the hydration of sodium carbonate (find the X in Na2CO3.XH2O).

Basically, I propose two methods of doing it:

1. Make a solution of known concentration and do a titration.
2. Heat the solid chemicals.

Method No. 1 is well known and comprehensible but requires more detailed explanation and precautions.
Method No. 2 is easier to write and describe, in terms of experiment and precautions. However, this method may require us to know a certain terms and apparatus.

I'll explain the first method first.

The first method is fairly simple. You just need to dissolve a known amount (in gram) sodium carbonate in distilled water and commence a titration with hydrochloric acid.

Since in titration, hydrochloric acid will only react with sodium carbonate, hence by finding the concentration of sodium carbonate reacted (in g/dm3), we can determine the mass of the water in the sodium carbonate, hence the hydration number (or whatever it is called).

The second method works exactly like our Paper 3 Question Number 2. Here, you need to heat with Bunsen Burner a known amount of hydrated sodium carbonate. This way, the water inside the sodium carbonate will be evaporated. The decrease in mass will signify the mass of water evaporated and hence we can find how much water originally in the crystal by comparing the mass of sodium carbonate with the water inside it.

Some apparatus required for these experiments:

• Test tubes, as the container for sodium carbonate
• Pipette, to transfer exactly 25 mL of solution of sodium carbonate for method 1
• Burette, to do the titration.
• Beaker, to contain the result 25 mL of solution of sodium carbonate.
• White tile
• Bunsen Burner, for method 2
  
• Boiling tube, to contain the sodium carbonate in method 2
• Anything to hold boiling tube while it is heated
• Weighing machine, to measure the mass of materials in method 2
• Stirrer and funnel to transfer the chemicals carefully.

I would say that is all for apparatus. Any extra advice would be appreciated.

Now for the chemicals:

• Hydrochloric acid, 0.125 mol/dm3, 250-400 mL
• Aqua destilata, a cool name for distilled water
• Sodium carbonate, of course. It must be pure.
• Methane or ethane, to fuel our bunsen burner.
• Indicator, any will do I think.

That is all for chemicals. Any extra addition will be deeply appreciated.

For the method No. 1, we just need to write what we usually do plus add some precautions and details, such as add X drops of indicator and indicate when we need to stop. For the table, just copy from any old past paper.

For method number 2, what I can say is that we need to continuously reheat and cool it down. We need to do this until the mass is finally constant, that is when all water is evaporated.

Suggestion for table.
Method 1:

Method 2:


So that is all I can help you. Good luck and if you have any problem you can approach Wind, Ms. Ine Medyawati or Kawapada.

Thank you.






(As a side note, if you can check the freeexampapers.com, you can see the paper 3 O/N 2001 and 2003 to get more reference)