炭酸マグネシウムは強電解質ですか? 明確な答え & Explanation

Is magnesium carbonate a strong electrolyte? No—it’s a 弱い (or very weak) electrolyte due to extremely low solubility in water. Learn why it doesn’t conduct well and how it compares to true strong electrolytes.

I’ve spent years specifying magnesium compounds for industrial clients, and the question is magnesium carbonate a strong electrolyte pops up more often than you’d think.

Usually from formulators checking conductivity for a process, or students prepping for exams, or even quality control folks testing suspensions.

The direct answer: いいえ, magnesium carbonate is not a strong electrolyte.

In fact, it’s best classified as a very weak electrolyte—or practically a non-electrolyte in most practical contexts.

Here’s why that distinction matters and what actually happens when you try to dissolve it.

What Makes a Strong Electrolyte?

Strong electrolytes fully (or nearly fully) dissociate into ions in water.

This creates a high concentration of mobile ions → excellent electrical conductivity.

Classic examples:

• NaCl → Na⁺ + Cl⁻ (complete)
• HCl → H⁺ + Cl⁻ (complete)
• MgCl₂ → Mg²⁺ + 2Cl⁻ (complete)

These solutions light up a conductivity bulb brightly.

Weak electrolytes only partially dissociate.

Examples: acetic acid (CH₃COOH), ammonia (NH₃).

Very low dissociation → dim or no light on the bulb.

Non-electrolytes don’t produce ions at all (sugar, ethanol).

Magnesium carbonate falls into the weak/near-non category because of one key property.

Why Magnesium Carbonate Isn’t a Strong Electrolyte

炭酸マグネシウム (mgco₃) has extremely low solubility in water.

Solubility ≈ 0.01–0.02 g per 100 mL at room temperature (about 10⁻⁴ M).

That’s tiny.

Even though it’s an ionic compound (Mg²⁺ and CO₃²⁻), almost none of it dissolves.

What little does dissolve does dissociate into ions:

mgco₃ (s) ⇌ Mg²⁺ (アクア) + CO₃²⁻ (アクア)

But the equilibrium lies far to the left.

KSP (溶解度積) ≈ 3.5 × 10⁻⁸ to 10⁻⁹ range depending on source.

Very small Ksp → very few ions in solution.

Result: negligible electrical conductivity.

In conductivity tests, a saturated MgCO₃ solution barely registers compared to even dilute NaCl.

So it’s not a strong electrolyte.

Many sources call it a weak electrolyte because a trace amount does ionize.

In strict classroom terms, some list it as non-electrolyte since conductivity is practically zero.

But the precise answer: very weak electrolyte due to insolubility limiting ion production.

Real-World Implications

Low ion concentration is why magnesium carbonate behaves the way it does:

• Stays as a stable powder in humid environments (no caking from dissolution).
• Used in gym chalk — absorbs sweat without turning into conductive slurry.
• Functions as filler in rubber/plastics — doesn’t leach ions that could interfere.

If it were a strong electrolyte like MgCl₂, it would dissolve readily, create high ion levels, and change conductivity dramatically.

A quick story from a client:

A coatings formulator added magnesium carbonate to thicken a water-based paint.

They tested conductivity expecting issues (high ions = instability).

Turned out conductivity stayed low — exactly because so little dissolved.

Saved them reformulation time.

Had it been a soluble salt, the batch would have flocculated or separated.

Comparison Table: Electrolyte Strength

You see the pattern: solubility drives ion availability, which drives electrolyte strength.

よくある質問

Is magnesium carbonate a strong electrolyte or weak? Neither strong nor meaningfully weak—it’s very weakly electrolytic because of near-insolubility. Practically negligible conductivity.

Does magnesium carbonate conduct electricity in water? Only minimally. A saturated solution has very low conductivity due to few ions.

Why isn’t MgCO₃ considered a strong electrolyte like MgCl₂? MgCl₂ is highly soluble and fully dissociates. MgCO₃ barely dissolves, so few ions form.

Is gym chalk (炭酸マグネシウム) an electrolyte? No—its low solubility keeps it from producing significant ions, even when wet with sweat.

Can magnesium carbonate affect pH or conductivity in formulations? Only slightly. It imparts mild alkalinity if any dissolves, but conductivity impact is tiny compared to soluble salts.

結論: is magnesium carbonate a strong electrolyte? No—its ultra-low solubility prevents it from behaving like one.

That’s the feature that makes it so useful in powders, フィラー, and chalk applications.