How do I dissolve Magnesium chloride (hexahydrate)? Its so hard!!?

Question

I have tried dissolving MgCl2.6H2O in water (100ml). Failing that, I tried dissolving the compound on a heat block...failing that (!!) i tried pH'ing whilst dissolving....nothing works! But I'm told that the solution can definately be made - but how??? Any ideas?? By the way, I need to make 4.5M MgCl2 (its for the elution stage of an affinity chromatography procedure)

Thanx for everyone's thoughts on this.. afraid to say that, yes, the solution MUST be this concentrated, else the procedure just won't work. And also, I've managed to get the MgCl2 to dissolve (hurray!)..so yesm it CAN be done..just use a hydrated form of the compound but this means taking into account that the additional H20 molecules add to the overall volume.. Adding MgCl2 to water doesn't work, especially when the amount of solute (91.5g) is so large and volume of water is just 100ml. And yes, its a very exothermic reaction so a lot of huffing and puffing of smoke and MgCl2 clouds when I tried to dissolve the anhydrous form. Thank you for everyone's thoughts on this issue.. now for the next part of the experiment.......

Answer 1

Whatever, I just answer for the points.

Answer 2

Try adding the magnesium chloride slowly to the water keeping it stirring on a stirrer hot plate, let each part dissolve before adding more. pHing it as you go may help as well. I have similar problems making up 8M urea as it is so close to the limit of it's solubility. You have to put in almost all of the water before it has fully dissolved as well. I find if I leave something stirring overnight it generally will have dissolved by the morning.

Good luck.

p.s this may seem obvious but don't store it in the fridge it'll just drop out of solution again.

It may be easier to dissolve anhydrous MgCl2, if the protocol does not specify hexahydrate you could try that.

Answer 3

I would suggest that this is one occasion where you need to add the water to the MgCl2 instead of the other way around. Start by making a 'paste' and slowly add more and more solvent while stirring, until you have the required concentration.

Many 'soluble' chemicals that won't dissolve directly when added to water can be turned into solutions this way. Just be sure the chemical in question doesn't react with the solvent first, otherwise you won't get a solution, probably you'll get a small explosion !

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Answer 5

Wow, 4.5M. I'm surprised that you can make a solution of MgCl2 that concentrated.

Anyhow, if it's part of a protocol then I assume it is possible. Like the above answer said, stirring it with heat will help. I would slowly add MgCl2 to the solution, not dump it all in at once. If it needs to be pHd then doing that as you add MgCl2 might aid in the process.

Keep in mind that if it takes heating the solution way up to make it work, that you might come in to the lab in the morning and find that it's come out of solution (happened to me in my old lab all the time because at night they let it ge tto like 50F :P)

Answer 6

Keep it well stirred. Use a magnetic stirrer if you have one. The solid tends to sink to the bottom and create a supersaturated solution and this prevents further dissolving. For substances like this I made myself a glass 'cruncher.' Take a piece of solid glass (stirring) rod. Heat one end in a Bunsen flame until it softens and then press the end down vertically on a heat proof surface. Repeat this until the end is splayed out like a flat headed nail. Let it cool. Use the flat head to crunch the bits of solid against the bottom of a beaker. It takes a bit of time but does work.

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Answer 8

2

Answer 9

1

Answer 10

Probably best to ask your lecturer. It's a bit high tech for Yahoo answers.

Answer 11

Magnesium chloride is composed of magnesium and chlorine and is a typical ionic halide, being highly polar and soluble in water. It is a weak Lewis acid, so not surprisingly the hexahydrate can undergo partial hydrolysis when heated. Magnesium chloride can be extracted from brine or sea water, and is a commonly used source of magnesium metal, which can be extracted from MgCl2 using electrolysis. In 1990, US production was around one million tonnes, with a bulk price around $180 per tonne.

Contents [hide]
1 Chemical properties
2 Preparation
3 Uses
3.1 Culinary use
3.2 Use as an anti-icer
3.3 Use in Hydrogen Storage
4 Precautions
5 References
6 External links
7 Suppliers/Manufacturers



[edit] Chemical properties
Magnesium chloride can serve as a source of magnesium compounds, for example by precipitation:

MgCl2(aq) + Ca(OH)2(aq) → Mg(OH)2(s) + CaCl2(aq)

It can be electrolysed to give magnesium metal:

MgCl2(l) → Mg(l) + Cl2(g)

Both of these reactions are used in the Dow process for production of metallic magnesium.[3] Unlike aluminium chloride, hydrated MgCl2 can be dehydrated without hydrolysis (under certain conditions). This allows anhydrous MgCl2 to be used as a cheap source of the metal via electrolysis.

Magnesium chloride can also act as a weak Lewis acid, and salts containing the MgCl42- are known, though rare.[2]


[edit] Preparation
In the Dow process, magnesium chloride is regenerated from magnesium hydroxide using hydrochloric acid:

Mg(OH)2(s) + 2 HCl → MgCl2(aq) + 2 H2O(l)

It may also be prepared from magnesium carbonate by a similar reaction.


[edit] Uses
Magnesium chloride is used for a variety of applications, besides the manufacture of magnesium via the Dow process discussed above. It is used in the manufacture of textiles, paper, fireproofing agents, cements and refrigeration brine.[3]


[edit] Culinary use
Magnesium chloride is an important coagulant used in the preparation of tofu from soy milk. In Japan it is sold as nigari (the term is derived from the Japanese word for "bitter"), a white powder produced from seawater after the sodium chloride has been removed, and the water evaporated. Nigari consists mostly of magnesium chloride, with some magnesium sulfate and other trace elements.


[edit] Use as an anti-icer
A number of state highway departments throughout the United States have decreased the use of rock salt and sand on roadways and have increased the use of liquid magnesium chloride as a de-icer or anti-icer. The liquid magnesium chloride is sprayed on dry pavement (tarmac) prior to precipitation or wet pavement prior to freezing temperatures in the winter months to prevent snow and ice from adhering and bonding to the roadway. The application of anti-icers is utilized in an effort to improve highway safety. The use of this product seems to show an improvement in driving conditions during and after freezing precipitation yet it seems to be negatively affecting electric utilities.

Two main issues have been raised regarding the anti-icer magnesium chloride as it relates to electric utilities: contamination of insulators causing tracking and arcing across them, and corrosion of steel and aluminium poles and pole hardware.


[edit] Use in Hydrogen Storage
Magnesium chloride has shown promise as a storage material for hydrogen. Ammonia, which is rich in hydrogen atoms, is used as an intermediate storage material. Ammonia can be effectively absorbed to solid Magnesium chloride, forming Mg(NH3)6Cl2. Ammonia is released by mild heat, and is then passed through a catalyst to give hydrogen gas.

Systematic name Magnesium chloride
Molecular formula MgCl2 (anhydrous)
MgCl2.6H2O (hexahydrate)
Molar mass 95.211 g/mol (anhydrous)
203.31 g/mol (hexahydrate)
Appearance white or colourless crystalline solid
CAS number [7786-30-3] (anhydrous)
[7791-18-6] (hexahydrate)
Properties
Density and phase 2.32 g/cm3 (anhydrous solid)
1.56 g/cm3 (hexahydrate solid)
Solubility in water 54.2 g/100 cm3 (20 °C)
Solubility in ethanol 7.4 g/100 cm3 (30 °C)
Melting point 714 °C (987 K)
Boiling point 1412 °C (1685 K)
Structure
Coordination
geometry (octahedral, 6-coordinate?)
Crystal structure CdCl2
Dipole moment ? D
Hydrates Hexahydrate
Hazards
MSDS Magnesium chloride MSDS
Main hazards irritant
NFPA 704
Flash point ?°C
R/S statement R: ?
S: ?
RTECS number ?
Supplementary data page
Structure and
properties n, εr, etc.
Thermodynamic
data Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS


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