The Magnesium Sulfate Formula is MgSO₄, representing a white crystalline ionic compound formed by one magnesium cation (Mg²⁺) and one sulfate anion (SO₄²⁻). This compound is covered in NCERT Chemistry for Class 10 and Class 11 under ionic compounds, chemical bonding, and salt chemistry. It is also relevant for NEET and JEE aspirants studying inorganic chemistry and solution chemistry. This article covers the formula, molecular structure, molar mass, properties, a complete formula sheet, three solved examples, CBSE exam tips, and important FAQs.
Key Magnesium Sulfate Formulas at a Glance
Quick reference for the most important formulas related to Magnesium Sulfate.
- Chemical formula: MgSO₄
- Hydrated form (Epsom salt): \( \text{MgSO}_4 \cdot 7\text{H}_2\text{O} \)
- Molar mass of MgSO₄: \( M = 24.31 + 32.07 + 4(16.00) = 120.37 \text{ g/mol} \)
- Molar mass of MgSO₄·7H₂O: \( M = 120.37 + 7(18.02) = 246.51 \text{ g/mol} \)
- Dissociation in water: \( \text{MgSO}_4 \rightarrow \text{Mg}^{2+} + \text{SO}_4^{2-} \)
- Percentage composition of Mg: \( \%\text{Mg} = \frac{24.31}{120.37} \times 100 \)
What is Magnesium Sulfate Formula?
The Magnesium Sulfate Formula, written as MgSO₄, represents an inorganic salt composed of magnesium, sulfur, and oxygen. It belongs to the family of sulfate salts. Magnesium is an alkaline earth metal in Group 2 of the periodic table. It forms a stable 2+ cation. The sulfate group (SO₄²⁻) carries a 2− charge. These two ions combine in a 1:1 ratio to form the electrically neutral compound MgSO₄.
In its most familiar form, magnesium sulfate exists as the heptahydrate \( \text{MgSO}_4 \cdot 7\text{H}_2\text{O} \), commonly known as Epsom salt. This hydrated form is widely used in medicine, agriculture, and industrial processes. The anhydrous form, MgSO₄, is a white powder used as a desiccant and drying agent in chemistry laboratories.
NCERT Chemistry Class 10 (Chapter 2 — Acids, Bases and Salts) and Class 11 (Chapter 4 — Chemical Bonding and Molecular Structure) provide the conceptual foundation for understanding this compound. Students studying salt formation, ionic bonding, and hydration of salts will encounter MgSO₄ frequently. It is also referenced in NCERT Class 11 Chapter 10 (The s-Block Elements) under magnesium compounds.
Magnesium Sulfate Formula — Expression and Variables
The chemical formula for magnesium sulfate is:
\[ \text{MgSO}_4 \]
The hydrated form, Epsom salt, is expressed as:
\[ \text{MgSO}_4 \cdot 7\text{H}_2\text{O} \]
The molar mass is calculated as:
\[ M(\text{MgSO}_4) = 24.31 + 32.07 + 4 \times 16.00 = 120.37 \text{ g/mol} \]
| Symbol / Component | Element / Group | Atomic / Molecular Mass (g/mol) | Count in Formula |
|---|---|---|---|
| Mg | Magnesium | 24.31 | 1 |
| S | Sulfur | 32.07 | 1 |
| O | Oxygen | 16.00 | 4 |
| MgSO₄ | Magnesium Sulfate (anhydrous) | 120.37 | — |
| MgSO₄·7H₂O | Magnesium Sulfate Heptahydrate (Epsom salt) | 246.51 | — |
Structure of Magnesium Sulfate
In the MgSO₄ formula, magnesium exists as Mg²⁺ and the sulfate group exists as SO₄²⁻. The sulfate ion has a tetrahedral geometry. The central sulfur atom forms four equivalent S–O bonds. The bond angle in the sulfate ion is approximately 109.5°, consistent with sp³ hybridisation of sulfur. In the crystal lattice, Mg²⁺ ions are surrounded by oxygen atoms from the sulfate groups. In the heptahydrate form, seven water molecules coordinate with each magnesium ion and sulfate ion through hydrogen bonding.
Derivation of Molar Mass
The molar mass of MgSO₄ is derived by adding the atomic masses of all constituent atoms.
Step 1: Identify atoms — 1 Mg, 1 S, 4 O.
Step 2: Use standard atomic masses: Mg = 24.31, S = 32.07, O = 16.00.
Step 3: Calculate: \( M = 24.31 + 32.07 + (4 \times 16.00) = 24.31 + 32.07 + 64.00 = 120.38 \text{ g/mol} \)
For the heptahydrate: \( M = 120.38 + 7 \times 18.02 = 120.38 + 126.14 = 246.52 \text{ g/mol} \)
Physical and Chemical Properties of Magnesium Sulfate
Understanding the properties of MgSO₄ is important for CBSE and competitive exams. The key properties are listed below.
| Property | Anhydrous MgSO₄ | MgSO₄·7H₂O (Epsom Salt) |
|---|---|---|
| Appearance | White crystalline powder | Colourless monoclinic crystals |
| Molar Mass | 120.37 g/mol | 246.51 g/mol |
| Melting Point | 1124 °C | Dehydrates at ~70 °C |
| Solubility in Water | Highly soluble (26.9 g/100 mL at 0 °C) | Highly soluble |
| Density | 2.66 g/cm³ | 1.68 g/cm³ |
| pH of solution | ~6.0 (slightly acidic) | ~6.0 |
| Nature | Ionic, hygroscopic | Ionic, crystalline |
Complete Chemistry Formula Sheet — Sulfate Salts and Related Compounds
| Formula Name | Expression | Variables / Components | Molar Mass (g/mol) | NCERT Chapter |
|---|---|---|---|---|
| Magnesium Sulfate | \( \text{MgSO}_4 \) | Mg²⁺, SO₄²⁻ | 120.37 | Class 10, Ch 2; Class 11, Ch 10 |
| Magnesium Sulfate Heptahydrate (Epsom Salt) | \( \text{MgSO}_4 \cdot 7\text{H}_2\text{O} \) | MgSO₄ + 7 water molecules | 246.51 | Class 10, Ch 2 |
| Barium Sulfate | \( \text{BaSO}_4 \) | Ba²⁺, SO₄²⁻ | 233.39 | Class 11, Ch 10 |
| Zinc Sulfate | \( \text{ZnSO}_4 \) | Zn²⁺, SO₄²⁻ | 161.47 | Class 11, Ch 12 |
| Copper Sulfate | \( \text{CuSO}_4 \) | Cu²⁺, SO₄²⁻ | 159.61 | Class 10, Ch 1 |
| Sodium Sulfate | \( \text{Na}_2\text{SO}_4 \) | 2 Na⁺, SO₄²⁻ | 142.04 | Class 10, Ch 2 |
| Ammonium Sulfate | \( (\text{NH}_4)_2\text{SO}_4 \) | 2 NH₄⁺, SO₄²⁻ | 132.14 | Class 11, Ch 8 |
| Calcium Sulfate (Plaster of Paris) | \( \text{CaSO}_4 \cdot \frac{1}{2}\text{H}_2\text{O} \) | Ca²⁺, SO₄²⁻, 0.5 H₂O | 145.15 | Class 10, Ch 2 |
| Iron(II) Sulfate | \( \text{FeSO}_4 \) | Fe²⁺, SO₄²⁻ | 151.91 | Class 10, Ch 1 |
| Magnesium Chloride | \( \text{MgCl}_2 \) | Mg²⁺, 2 Cl⁻ | 95.21 | Class 11, Ch 10 |
Magnesium Sulfate Formula — Solved Examples
Example 1 (Class 9-10 Level) — Calculating Molar Mass
Problem: Calculate the molar mass of magnesium sulfate (MgSO₄) using standard atomic masses.
Given: Atomic mass of Mg = 24.31 g/mol, S = 32.07 g/mol, O = 16.00 g/mol
Step 1: Write the formula: \( \text{MgSO}_4 \)
Step 2: Count each atom — 1 Mg, 1 S, 4 O.
Step 3: Multiply each atomic mass by its count:
\( M = (1 \times 24.31) + (1 \times 32.07) + (4 \times 16.00) \)
Step 4: Add the values:
\( M = 24.31 + 32.07 + 64.00 = 120.38 \text{ g/mol} \)
Answer
Molar mass of MgSO₄ = 120.38 g/mol
Example 2 (Class 11-12 Level) — Percentage Composition
Problem: Calculate the percentage by mass of magnesium, sulfur, and oxygen in MgSO₄.
Given: Molar mass of MgSO₄ = 120.38 g/mol; Mg = 24.31 g/mol; S = 32.07 g/mol; O = 16.00 g/mol
Step 1: Use the formula: \( \% \text{ element} = \frac{\text{mass of element in 1 mol}}{\text{molar mass of compound}} \times 100 \)
Step 2: Percentage of Mg:
\( \%\text{Mg} = \frac{24.31}{120.38} \times 100 = 20.20\% \)
Step 3: Percentage of S:
\( \%\text{S} = \frac{32.07}{120.38} \times 100 = 26.64\% \)
Step 4: Percentage of O (4 oxygen atoms):
\( \%\text{O} = \frac{64.00}{120.38} \times 100 = 53.17\% \)
Step 5: Verify: \( 20.20 + 26.64 + 53.17 = 100.01\% \approx 100\% \) ✓
Answer
%Mg = 20.20%, %S = 26.64%, %O = 53.17%
Example 3 (JEE/NEET Level) — Moles and Number of Ions in Solution
Problem: 24.076 g of anhydrous magnesium sulfate (MgSO₄) is dissolved completely in water to form 500 mL of solution. Calculate (a) the number of moles of MgSO₄, (b) the molarity of the solution, and (c) the total number of ions present in the solution. (Given: Avogadro’s number = \( 6.022 \times 10^{23} \) mol⁻¹, molar mass of MgSO₄ = 120.38 g/mol)
Given: Mass = 24.076 g; Volume = 500 mL = 0.5 L; \( N_A = 6.022 \times 10^{23} \) mol⁻¹
Step 1: Calculate moles of MgSO₄:
\( n = \frac{\text{mass}}{\text{molar mass}} = \frac{24.076}{120.38} = 0.2000 \text{ mol} \)
Step 2: Calculate molarity (M):
\( M = \frac{n}{V(\text{in L})} = \frac{0.2000}{0.5} = 0.400 \text{ mol/L} \)
Step 3: Write the dissociation equation:
\( \text{MgSO}_4 \rightarrow \text{Mg}^{2+} + \text{SO}_4^{2-} \)
Each formula unit gives 2 ions (1 Mg²⁺ and 1 SO₄²⁻).
Step 4: Calculate total number of ions:
\( \text{Total ions} = 2 \times n \times N_A = 2 \times 0.2000 \times 6.022 \times 10^{23} \)
\( = 2.409 \times 10^{23} \text{ ions} \)
Answer
(a) Moles of MgSO₄ = 0.200 mol
(b) Molarity = 0.400 M
(c) Total ions = 2.409 × 10²³
CBSE Exam Tips 2025-26 for Magnesium Sulfate Formula
- Memorise the formula correctly: Write MgSO₄ — not MgSO₃ or Mg₂SO₄. The magnesium ion is Mg²⁺ and sulfate is SO₄²⁻. They combine in a 1:1 ratio.
- Know both forms: CBSE often asks about the hydrated form. Epsom salt is \( \text{MgSO}_4 \cdot 7\text{H}_2\text{O} \). Remember the 7 water molecules.
- Molar mass calculation: In board exams 2025-26, always show your working step by step. Write each element, its count, and its atomic mass separately before summing.
- Distinguish anhydrous vs. hydrated: Anhydrous MgSO₄ is a desiccant (absorbs moisture). The hydrated form (Epsom salt) is used in medicine. This distinction appears in application-type questions.
- We recommend practising percentage composition problems using MgSO₄ as they appear frequently in Class 11 Chapter 1 (Some Basic Concepts of Chemistry) numericals.
- Ionic equation: Always write the dissociation equation \( \text{MgSO}_4 \rightarrow \text{Mg}^{2+} + \text{SO}_4^{2-} \) when asked about electrolytic behaviour or conductivity.
Common Mistakes to Avoid with Magnesium Sulfate Formula
- Wrong formula — MgSO₃ instead of MgSO₄: Magnesium sulfite is MgSO₃. Magnesium sulfate is MgSO₄. The sulfate ion always has 4 oxygen atoms. Sulfite has 3. Confusing these two is a very common error in CBSE board exams.
- Incorrect molar mass of heptahydrate: Many students forget to add the mass of 7 water molecules. The molar mass of MgSO₄·7H₂O is 120.38 + 7(18.02) = 246.51 g/mol, not 120.38 g/mol.
- Wrong charge on magnesium ion: Magnesium always forms a 2+ ion (Mg²⁺), not Mg⁺. This affects how you write the formula and the dissociation equation.
- Forgetting to count both ions in molarity problems: When MgSO₄ dissolves, it produces 2 ions per formula unit. Forgetting to multiply by 2 when calculating total ion concentration is a frequent JEE mistake.
- Confusing Epsom salt with common salt: Common salt is NaCl. Epsom salt is MgSO₄·7H₂O. These are completely different compounds with different uses and properties.
JEE/NEET Application of Magnesium Sulfate Formula
In our experience, JEE aspirants encounter the Magnesium Sulfate Formula in several important contexts across inorganic chemistry, solution chemistry, and electrochemistry.
1. Mole Concept and Stoichiometry (JEE Main / NEET)
MgSO₄ is a classic compound used in mole concept problems. Questions typically ask you to calculate moles from a given mass, find the number of formula units, or determine the mass of a specific element in a sample. The key formula is:
\[ n = \frac{m}{M} \]
where \( n \) = moles, \( m \) = mass in grams, and \( M \) = molar mass in g/mol. For MgSO₄, \( M = 120.38 \) g/mol.
2. Solution Chemistry and Molarity (JEE Advanced)
JEE Advanced problems often combine molarity, dissociation, and colligative properties using electrolytes like MgSO₄. Since MgSO₄ is a strong electrolyte, it dissociates completely:
\[ \text{MgSO}_4 \rightarrow \text{Mg}^{2+} + \text{SO}_4^{2-} \]
The van’t Hoff factor \( i = 2 \) for MgSO₄ in dilute solution. This value is used in colligative property calculations such as depression of freezing point and elevation of boiling point.
3. Qualitative Analysis and s-Block Chemistry (NEET)
NEET questions on s-block elements (Class 11, Chapter 10) test knowledge of magnesium compounds. The Magnesium Sulfate Formula appears in reactions involving magnesium with dilute sulfuric acid:
\[ \text{Mg} + \text{H}_2\text{SO}_4 \rightarrow \text{MgSO}_4 + \text{H}_2 \uparrow \]
Our experts suggest that NEET students also remember that magnesium sulfate solution gives a white precipitate of BaSO₄ with barium chloride solution. This is a key confirmatory test for the sulfate ion.
\[ \text{MgSO}_4 + \text{BaCl}_2 \rightarrow \text{BaSO}_4 \downarrow + \text{MgCl}_2 \]
FAQs on Magnesium Sulfate Formula
Explore More Chemistry Formulas
We hope this comprehensive guide to the Magnesium Sulfate Formula has helped you understand the compound’s structure, molar mass, properties, and applications. For further study, explore these related resources on ncertbooks.net:
- Visit the Complete Chemistry Formulas Hub for a full list of inorganic and organic compound formulas.
- Learn about the Barium Acetate Formula to understand another important ionic salt used in CBSE and JEE chemistry.
- Study the Zinc Bromide Formula for more practice with transition metal salt formulas and molar mass calculations.
- Revise the Ammonium Acetate Formula to strengthen your understanding of salt formation and buffer chemistry.
For official NCERT textbook references, visit the NCERT official website to access the Class 10 and Class 11 Chemistry textbooks online.