The Chemistry of Magnesium and Heat
Magnesium is a mineral, which is a stable element found in the periodic table. It does not simply evaporate or get destroyed by the temperatures achieved when boiling water (100°C or 212°F). Its boiling point is much higher, at around 1090°C. Therefore, the magnesium itself remains in the water, but its chemical form and concentration can change depending on the water's initial composition.
The Role of Water Hardness
The most significant change related to magnesium during boiling involves water hardness. Water hardness is caused by high concentrations of dissolved minerals, primarily calcium and magnesium. There are two types of hardness:
- Temporary Hardness: This is caused by dissolved bicarbonates of calcium and magnesium.
- Permanent Hardness: This is caused by other salts like sulfates and chlorides of calcium and magnesium.
When you boil water, the heat drives off dissolved carbon dioxide ($$CO_2$$). This triggers a chemical reaction where soluble bicarbonates convert into less soluble carbonates, which then precipitate out as a solid. This is the chemical process behind the limescale you see in your kettle or pots. For magnesium, the reaction looks like this:
$$Mg(HCO_3)_2(aq) \xrightarrow{Heat} MgCO_3(s) + H_2O(l) + CO_2(g)$$
This means that some of the dissolved magnesium becomes an insoluble solid, effectively reducing the dissolved magnesium content in the water.
Concentration, Not Destruction
While some magnesium may precipitate out due to temporary hardness, the minerals responsible for permanent hardness, such as magnesium sulfate, are not affected by boiling. Furthermore, as the water boils and turns into steam, the volume of water decreases. The minerals that remain dissolved become more concentrated in the reduced volume of liquid. So, if you boil off half the water, the remaining water will have a higher concentration of the minerals that did not precipitate out, including some forms of magnesium.
Comparison of Water Treatment Methods
To understand the true impact, it's helpful to compare boiling with other water treatment methods.
| Treatment Method | Affects Magnesium Content | Affects Water Hardness | Primary Purpose | Residuals |
|---|---|---|---|---|
| Boiling | Yes (precipitates some, concentrates others) | Reduces temporary hardness only | Kills microorganisms (disinfection) | Mineral concentration increases; limescale forms |
| Distillation | Removes virtually all magnesium | Completely removes all hardness | Water purification; removes minerals, chemicals, and microbes | Pure water (distillate); impurities left behind |
| Ion Exchange Softener | Removes magnesium (and calcium) | Completely removes all hardness | Water softening; replaces hardness ions with sodium or potassium | Water is soft; elevated sodium levels |
| Reverse Osmosis (RO) | Removes most minerals, including magnesium | Completely removes all hardness | High-level purification; removes most contaminants | Clean water; creates wastewater with concentrated minerals |
Practical Implications and Uses
For everyday cooking and drinking, the effect of boiling on magnesium content is negligible from a nutritional standpoint. The amount of magnesium gained or lost is minimal compared to dietary intake from other food sources. However, the process is extremely effective at disinfecting water by killing most waterborne pathogens.
If the water is very hard, boiling will make it slightly less hard by removing some of the mineral content, which is why it can reduce the build-up of limescale over time in kettles. For those concerned about the absolute purity of their water, boiling is not the solution, as it concentrates non-volatile contaminants like lead and nitrates. For truly demineralized water, distillation is required.
Conclusion
In conclusion, boiling water does not destroy magnesium. The mineral is a stable element that withstands the temperature of boiling. For water with temporary hardness (bicarbonates), some magnesium will precipitate out as a solid, leaving less dissolved mineral in the water. For all other soluble forms of magnesium, the process of boiling actually leads to a higher concentration as water evaporates. Boiling is a valuable method for sterilizing water against biological pathogens, but it should not be relied upon for removing chemical contaminants or significantly altering mineral content for health reasons. Ultimately, the best way to ensure you are getting enough magnesium is through a balanced diet. For more information on magnesium and its health benefits, you can consult the National Institutes of Health (NIH).
Frequently Asked Questions
How does boiling water affect the mineral concentration in general?
As water evaporates during boiling, the minerals that are not volatile, including magnesium, remain in the pot. This results in a higher concentration of minerals in the remaining volume of water.
Can I get all the magnesium I need from drinking boiled tap water?
While tap water contains magnesium, relying solely on boiled tap water is not a complete or reliable strategy for meeting your daily intake requirements. A balanced diet rich in leafy greens, nuts, and whole grains is a much better source.
Is magnesium found in all tap water?
Yes, magnesium is a common mineral found in varying concentrations in most tap water sources, contributing to its overall hardness. The exact amount depends on the geological sources of the water supply.
Is boiling water enough to remove all impurities?
No, boiling kills most microorganisms like bacteria and viruses but does not remove chemical impurities such as heavy metals (e.g., lead), pesticides, or nitrates. In fact, it can concentrate them.
What is the purpose of boiling water if it doesn't remove minerals?
Boiling water's primary purpose is to disinfect it by killing harmful pathogens and microorganisms, making it safe to drink during a boil-water advisory or in emergencies.
Does boiling hard water make it soft?
Boiling only reduces temporary hardness, which is caused by bicarbonates. It will not reduce permanent hardness caused by other salts like sulfates, which remain dissolved.
Why does boiled water sometimes have a different taste?
Boiling water drives off dissolved gases, primarily oxygen and carbon dioxide, which can leave the water with a 'flat' taste. Aerating the water (e.g., by pouring it between containers) can help restore some of the taste.
