How to Distinguish Sulphate, Sulphide and Sulphite Easily?
Understanding the difference between sulphate, sulphite, sulphide is crucial for JEE Main Chemistry as these ions frequently appear in chemical equations, reactions, and MCQs. They are common in inorganic compounds, have different structures and oxidation states, and are often confused in exams. Mastering this concept makes it easier to predict reactivity, perform qualitative analysis, and solve competitive questions with SO3, SO4, or S2− ions.
Definitions and Chemical Formulas: Sulphate, Sulphite, Sulphide
Sulphate (SO42−): A polyatomic anion with one sulphur atom surrounded by four oxygen atoms. The overall charge is 2−. Examples: Na2SO4 (sodium sulphate), BaSO4 (barium sulphate).
Sulphite (SO32−): Contains one sulphur atom bonded to three oxygen atoms. Overall charge is also 2−. Examples: Na2SO3, K2SO3.
Sulphide (S2−): A simple anion with only a sulphur atom carrying a 2− charge. Forms binary compounds with metals: FeS (iron sulphide), Na2S (sodium sulphide).
Comparison Table: Structure, Properties, Formulas
| Property | Sulphate (SO42−) | Sulphite (SO32−) | Sulphide (S2−) |
|---|---|---|---|
| Oxidation state of S | +6 | +4 | −2 |
| Formula | SO42− | SO32− | S2− |
| No. of oxygen atoms | 4 | 3 | 0 |
| Type of ion | Oxyanion | Oxyanion | Monoatomic anion |
| Acidity/Basicity in solution | Weak base | Moderate base; can act as reducing agent | Strong base |
| Common examples | Na2SO4, BaSO4 | Na2SO3, K2SO3 | FeS, Na2S |
This table helps quickly compare sulphate vs sulphite vs sulphide based on formulas, oxygen count, and oxidation state. Use this for last-minute revision and to avoid confusion in MCQs.
How to Distinguish: JEE Lab Tricks and Reactions
- For sulphate, add BaCl2 solution: a white precipitate of BaSO4 forms and is insoluble in HCl.
- Sulphite reacts with dilute H2SO4 to give SO2 gas (turns acidified K2Cr2O7 green).
- Both sulphate and sulphite form white BaSO4 and BaSO3 with BaCl2, but BaSO3 (from sulphite) dissolves in dilute HCl, while BaSO4 does not.
- Sulphide gives black precipitate with lead acetate (PbS). It also turns lead acetate paper black in presence of HCl.
Remember: SO3 vs SO4 is a classic MCQ trap. SO4 is sulphate (4 oxygens), SO3 is sulphite (3 oxygens).
Significance and Examples in Chemistry & Industry
- Sulphate ions are found in gypsum, fertilizers, and detergents. BaSO4 is used in X-rays.
- Sulphites act as food preservatives (E220–E228) and are common in paper pulping.
- Sulphides are important in metallurgy for ore extraction (e.g., ZnS in froth flotation).
- Environmental impact: SO2 gas (from sulphites) causes acid rain; sulphates are natural minerals in water hardness.
- In qualitative analysis, sulphide and sulphite identification helps in salt analysis practicals.
Carefully noting chemical formulas and oxidation states lets you answer reactions and applications involving sulphate, sulphite, sulphide efficiently in JEE Main Chemistry.
Sample MCQs and JEE Application
- Which ion has 3 oxygen atoms? (A) SO42− (B) SO32− (C) S2− (D) SO2
- On adding BaCl2 to a solution, a white ppt forms dissolving in HCl. What was present? (A) Sulphate (B) Sulphite (C) Sulphide (D) Nitrate
- Oxidation state of S in sulphate ion is: (A) −2 (B) +2 (C) +6 (D) +4
- Which species is monoatomic? (A) Sulphate (B) Sulphite (C) Sulphide (D) Nitrate
- What is the formula for sulphide ion? (A) SO42− (B) SO32− (C) S2− (D) O2−
Answers: 1-B; 2-B; 3-C; 4-C; 5-C. Confusing SO3 and SO4, or mixing up sulphate and sulphite, is a common error in speed tests.
Quick Revision Notes & Memory Tips
- SO42− is sulphate: 4 oxygens, S is +6. Think “SO4 = S O four = four O's”.
- SO32− is sulphite: 3 oxygens, S is +4. “SO3 = less than SO4: fewer oxygens, lower S oxidation.”
- S2− is sulphide: no oxygens, S is −2. Always forms simple binary salts.
- Lab: BaCl2 test for sulphate gives white ppt, not soluble in acid; for sulphite, ppt dissolves in acid.
- Sulphide forms black ppt with lead acetate, releases rotten egg smell (H2S).
For conceptual clarity on difference between sulphate sulphite sulphide in JEE, focus on the oxygen count, formula, and classic lab reactions. Always re-examine oxidation states in tricky MCQs. For deeper p-block study, visit p-block elements, or practice with real exam MCQs at chemistry important questions. More structural concepts are covered under chemical bonding and molecular structure and JEE-level coordination compounds topics at Vedantu.
FAQs on Difference Between Sulphate, Sulphide, and Sulphite: Complete Guide
1. What is the difference between sulphate, sulphite, and sulphide?
Sulphate, sulphite, and sulphide are distinct ions with different formulas, structures, and oxidation states.
Key differences include:
- Sulphate (SO42−): Contains four oxygen atoms, sulphur is in +6 oxidation state.
- Sulphite (SO32−): Contains three oxygen atoms, sulphur is in +4 oxidation state.
- Sulphide (S2−): Contains only sulfur with a -2 charge, no oxygen.
2. How to distinguish between SO3 and SO4 in chemistry?
You can distinguish SO32− (sulphite) and SO42− (sulphate) ions using laboratory tests:
- Barium chloride test: Both ions form a white precipitate of barium salts. However, barium sulphate (BaSO4) is insoluble in acids, while barium sulphite (BaSO3) dissolves in dilute acids with effervescence (releasing SO2 gas).
- Acid addition: Adding dilute HCl releases SO2 from sulphite but not from sulphate.
3. Are sulphate and sulphite the same?
No, sulphate (SO42−) and sulphite (SO32−) are different polyatomic ions:
- Sulphate has four oxygen atoms attached to sulphur in the +6 oxidation state.
- Sulphite has three oxygen atoms, and sulphur is in the +4 oxidation state.
4. Is sulphide the same as sulphate?
No, sulphide (S2−) and sulphate (SO42−) are very different:
- Sulphide contains only the sulphur ion with a -2 charge, no oxygen.
- Sulphate is a polyatomic ion with four oxygen atoms bonded to sulphur.
5. What is the formula of sulphate, sulphite, and sulphide?
Here are the standard formulas for each ion:
- Sulphate: SO42−
- Sulphite: SO32−
- Sulphide: S2−
6. How to remember the difference between sulphate and sulphite for exams?
You can use memory aids to distinguish sulphate and sulphite:
- "ate" usually means more oxygen; SO4 for sulphate (more oxygen); SO3 for sulphite (less oxygen).
- Remember: SO4 = four oxygens (sulphate); SO3 = three oxygens (sulphite).
7. What is the oxidation state of sulphur in sulphate, sulphite, and sulphide?
The oxidation state of sulphur is different in each ion:
- Sulphate (SO42−): +6
- Sulphite (SO32−): +4
- Sulphide (S2−): -2
8. What are some common examples and uses of sulphate, sulphite, and sulphide compounds?
Here are common compounds and their uses:
- Sulphate: Sodium sulphate (Na2SO4), Calcium sulphate (gypsum) – used in detergents, plaster, and fertilizers.
- Sulphite: Sodium sulphite (Na2SO3) – used as preservatives and in paper industry.
- Sulphide: Hydrogen sulphide (H2S), Iron sulphide (FeS) – used in industry and found in ores.
9. Can laboratory tests distinguish between sulphate, sulphite, and sulphide ions?
Yes, several lab tests can identify or distinguish these ions:
- Barium chloride test: Distinguishes sulphate (forms insoluble BaSO4) and sulphite (BaSO3 dissolves in acids).
- HCl addition: Sulphite releases SO2 gas (with pungent smell), sulphide gives H2S gas (rotten egg smell), sulphate does not react.
10. Why do students often confuse SO3 and SO4 in exams?
Students confuse SO3 (sulphite) and SO4 (sulphate) due to similar names and formulas:
- SO32− is sulphite (three oxygens, lower oxidation state), while SO42− is sulphate (four oxygens, higher oxidation state).
- Both are anions of sulphur and appear in similar contexts, leading to mistakes in MCQs.
11. Why is SO3 called sulphite and not sulphate?
SO32− is called sulphite because it has one fewer oxygen atom than sulphate (SO42−).
- The suffix '-ite' is used for oxyanions with less oxygen.
- Sulphate refers to SO42−, while sulphite refers to SO32−.
12. How are these ions important for JEE and NEET exams?
Questions on sulphate, sulphite and sulphide ions test your concept clarity in inorganic chemistry.
- Appear as MCQs, reaction mechanisms, and identification (qualitative analysis).
- Frequently used in formula-based, structure-based, and application-based problems.
