Sodium tetraborate

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  Sodium tetraborate   
Names: sodium tetraborate
disodium tetraborate
sodium borate
borax
tincal
tincalconite

Formula: Na2B4O7
Na2B4O7 · 5H2O
Na2B4O7 · 10H2O
SMILES: B1(OB2OB(OB(O1)O2)[O-])[O-].[Na+].[Na+]
Molar mass: 201.217 g/mol (anhydrous)
291.291 g/mol (pentahydrate)
381.366 g/mol (decahydrate)
Density: 2.37 g/cm3 (anhydrous)
1.815 g/cm3 (pentahydrate)
1.71 g/cm3 (decahydrate)
Crystal system: monoclinic (anhydrous)
a=5.507 Å
5.5070 Å
0.5507 nm
, b=17.796 Å
17.7960 Å
1.7796 nm
, c=8.377 Å
8.3770 Å
0.8377 nm
α=90°
90°  
, β=96.566°
96°33′57.6″  
, γ=90°
90°  

orthorhombic (pentahydrate)
α=90°
90°  
, β=90°
90°  
, γ=90°
90°  

monoclinic (decahydrate)
a=11.884 Å
11.8840 Å
1.1884 nm
, b=10.602 Å
10.6020 Å
1.0602 nm
, c=12.2111 Å
12.2111 Å
1.2211 nm
α=90°
90°  
, β=106.790°
106°47′24.0″  
, γ=90°
90°  

Forms:
https://media.crystalls.info/w/uploads/media/Prolongated_hexagonal_flat_prism.json


https://media.crystalls.info/w/uploads/media/Octahedron.json


https://media.crystalls.info/w/uploads/media/Tetragonal_pyramid.json


Color: colorless
Melting point: 742°C
1,015.15 K
1,367.6 °F
1,827.27 °R
(anhydrous)
140°C
413.15 K
284 °F
743.67 °R
(pentahydrate)
Decomposition point: 1575°C
1,848.15 K
2,867 °F
3,326.67 °R
(anhydrous)
62°C
335.15 K
143.6 °F
603.27 °R
(decahydrate)
320°C
593.15 K
608 °F
1,067.67 °R
(pentahydrate)
Refractive index: 1.462 (decahydrate)
1.468 (pentahydrate)
Electrical properties: dielectric
Magnetic properties: diamagnetic
Stability: slightly erodes (decahydrate)
stable (pentahydrate)
Hardness: relatively strong
Toxicity: non-toxic

Description

Inorganic compound, salt of alkaline metal sodium and inorganic tetraboric acid. From water solutions crystallizes as pentahydrate and decahydrate.

Minerals

Occurs in nature as tinkal mineral.

Where to buy

In pharmacy ("borax" as powder or glycerol solution).

Synthesis

Reaction between baking soda, sodium carbonate or hydroxide and boric acid

Chemical equation:

4H3BO3 + 2NaHCO3 = Na2B4O7 + 7H2O + 2CO2
4H3BO3 + Na2CO3 = Na2B4O7 + 6H2O + CO2
4H3BO3 + 2NaOH = Na2B4O7 + 7H2O

For preparation 100g of sodium tetraborate decahydrate a 44.06g of soda, 27.79g of carbonate or 20.98g of sodium hydroxide and 64.85g of boric acid is required.

Add acid to the flask, then add small parts of sodium compound with stirring until heating will stop (attention, the solution may boil!) or, if you use carbonate, until carbon dioxide emission will stop. After reaction will stop, filter the solution and use it for crystal growing.

Influence of temperature

Very slow crystallization and low transparency at room temperature, but growing from hot solution eliminates these drawbacks. If temperature is over decahydrate decomposition temperature, a pentahydrate crystallization starts with another crystalline final form.

Influence of impurities

Colorants can change the shape of the final crystal.

Storage conditions

Store in its original form or under several layers of varnish at average humidity and room temperature. Do not store in matchboxes or cotton wool and do not heat.

Notes

Crystal can thicken after several months due to eroding.

Solubility

Temperatureg/100g of waterg/100g of ethanolg/100g of methanolg/100g of acetoneg/100g of glycerolg/100g of ethyl acetateg/100g of ethylene glycol
(anhydrous)(pentahydrate)(decahydrate)(decahydrate)(decahydrate)(decahydrate)(decahydrate)(decahydrate)(decahydrate)
0°C
273.15 K
32 °F
491.67 °R
1.11
1.11 g/100g
1.098 %
2.04
2.04 g/100g
1.999 %
10°C
283.15 K
50 °F
509.67 °R
3.19
3.19 g/100g
3.091 %
15°C
288.15 K
59 °F
518.67 °R
3.94
3.94 g/100g
3.791 %
2.54
2.54 g/100g
2.477 %
20°C
293.15 K
68 °F
527.67 °R
4.94
4.94 g/100g
4.707 %
110.97
110.97 g/100g
52.6 %
25°C
298.15 K
77 °F
536.67 °R
6.16
6.16 g/100g
5.803 %
24.84
24.84 g/100g
19.897 %
0.6
0.6 g/100g
0.596 %
0.14
0.14 g/100g
0.14 %
71.23
71.23 g/100g
41.599 %
30°C
303.15 K
86 °F
545.67 °R
7.76
7.76 g/100g
7.201 %
40°C
313.15 K
104 °F
563.67 °R
12.64
12.64 g/100g
11.222 %
50°C
323.15 K
122 °F
581.67 °R
15.87
15.87 g/100g
13.696 %
21.82
21.82 g/100g
17.912 %
60°C
333.15 K
140 °F
599.67 °R
~17.9
17.9 g/100g
15.182 %
43.53
43.53 g/100g
30.328 %
70°C
343.15 K
158 °F
617.67 °R
20
20 g/100g
16.667 %
58.58
58.58 g/100g
36.94 %
80°C
353.15 K
176 °F
635.67 °R
23
23 g/100g
18.699 %
79.57
79.57 g/100g
44.311 %
90°C
363.15 K
194 °F
653.67 °R
28
28 g/100g
21.875 %
113.58
113.58 g/100g
53.179 %
100°C
373.15 K
212 °F
671.67 °R
52.5
52.5 g/100g
34.426 %
35
35 g/100g
25.926 %
191.04
191.04 g/100g
65.64 %

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