# Last edited on 2017-02-08 04:58:15 by jstolfi

EXPERIMENTS WITH SODIUM CARBONATE

  Molar mass of anhydrous Na2CO3: 106 g
  
  Hydrates: 
  
    Na2CO3(H2O)10 decahydrate decomposes at 34 C
    Na2CO3(H2O)7 heptahydrate decomposes at 33.5 C (!!)
    Na2CO3(H2O) monohydrate decomposes at 100 C
    
  Thus 106 g of anhydrous Na2CO3 should absorb 18 g of water to become
  the monohydrate, and 180 g of water (below 34 C) to become the
  decahydrate.
  
  Also 124 g of monohydrate should absorb (below 34 C) 162 g of water
  to become the decahydrate.
  
Solubility data:

    g_w["Na2CO3",   0] =   7.0;
    g_w["Na2CO3",  10] =  12.2;
    g_w["Na2CO3",  20] =  21.4;
    g_w["Na2CO3",  25] =  29.4;
    g_w["Na2CO3",  30] =  39.7;
    g_w["Na2CO3",  40] =  48.8;
    g_w["Na2CO3",  50] =  47.3;
    g_w["Na2CO3",  60] =  46.4;
    g_w["Na2CO3",  80] =  45.1;
    g_w["Na2CO3", 100] =  44.3;
    g_w["Na2CO3", 120] =  42.7;
    g_w["Na2CO3", 150] =  39.3;
    compute_g_w_hydrated("Na2CO3", 1);
    compute_g_w_hydrated("Na2CO3", 7);
    compute_g_w_hydrated("Na2CO3", 10);

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2017-02-04

  Preparation of anhydrous Na2CO3:
  
  Heated 25 g of Na2CO3(H2O)x (Agros) in a stainless steel cup
  to 120 C.  The crystalline powder became loose amorphous
  powder (E5) weighting 22 g.  That is consistent with the original
  being the monohydrate and the result (E5) being the anhydrous salt.

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2017-02-06

Preparing a standardized solution of Na2CO3

  Dissolved some Na2CO3 in ~50 ml water at ~28C. Put the solution (C0)
  in an ice bath to cool.
  
  At 10 C the solution (C0) was still clear.  However, rubbing the
  thermometer against the glass caused it to instantly crystallize
  into a mass of apparently soft crystals.  
  
  Filtered (C0) at 15 C.  (That seems to be a transition temperature
  since it stood there for a while.)  The filtrate (C2) was cooled
  to ~12 C.  Crystals formed.  Warmed gradually with stirring: crystals
  disappeared at 16 C.
  
  At 16 C, the solubility of Na2CO3 is about 13 g per 100 ml H2O.
  The solution is then 11.5% by weight.
  
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2017-02-07 Tue

  Re-heated the anydrous carbonate (E5), 18 g, in a stainless steel
  cup to 140 C for several minutes.  Let it cool.  Loose dust
  (E6), weight 17 g.