The Language of Chemistry — Question 17
Back to all questionsQuestion 12(6)
Write the formula of the following compounds :
Aluminium
| (a) | chloride | (b) | nitrate |
| (c) | carbonate | (d) | sulphate |
| (e) | hydroxide | (f) | oxide |
| Sl. No. | Compound | Formula |
|---|---|---|
| (a) | chloride | AlCl3 |
| (b) | nitrate | Al(NO3)3 |
| (c) | carbonate | Al2(CO3)3 |
| (d) | sulphate | Al2(SO4)3 |
| (e) | hydroxide | Al(OH)3 |
| (f) | oxide | Al2O3 |
Chapter Overview: Language of Chemistry
This foundational chapter introduces the symbolic language used in chemistry. Elements are represented by chemical symbols (one or two letters derived from their English or Latin names), compounds by chemical formulae showing the types and numbers of atoms, and reactions by chemical equations. Students learn to write formulae using the concept of valency - the combining capacity of an element. The criss-cross method helps in writing correct formulae of ionic compounds. Chemical equations represent reactions with reactants on the left and products on the right, separated by an arrow. A balanced equation has equal numbers of each type of atom on both sides (Law of Conservation of Mass). Students must master writing word equations, converting them to formula equations, and then balancing them. The chapter also covers types of chemical reactions: combination, decomposition, displacement, double decomposition, and neutralisation. Understanding this chapter is critical as chemical equations form the backbone of all subsequent chemistry topics.
Key Definitions
| Term | Definition |
|---|---|
| Symbol | Short representation of an element (e.g., Na for Sodium, Fe for Iron) |
| Valency | Combining capacity of an element (number of bonds it can form) |
| Chemical Formula | Representation showing types and numbers of atoms in a compound (e.g., H2O) |
| Molecular Formula | Shows actual number of atoms of each element in one molecule |
| Chemical Equation | Symbolic representation of a chemical reaction using formulae |
| Balanced Equation | Equal number of atoms of each element on both sides |
| Catalyst | Substance that changes reaction rate without being consumed |
Must-Know Concepts
- Common valencies: H(1), O(2), N(3), C(4), Na(1), Ca(2), Al(3), Fe(2,3), Cu(1,2)
- Polyatomic ions: OH−(1), SO42−(2), NO3−(1), CO32−(2), NH4+(1), PO43−(3)
- Criss-cross method: write valencies, cross them as subscripts, simplify
- Combination: A + B → AB (e.g., 2Mg + O2 → 2MgO)
- Decomposition: AB → A + B (e.g., 2H2O → 2H2 + O2)
- Displacement: A + BC → AC + B (e.g., Zn + CuSO4 → ZnSO4 + Cu)
- State symbols: (s) solid, (l) liquid, (g) gas, (aq) aqueous solution
Important Diagrams to Practice
- Criss-cross method worked examples for writing chemical formulae
- Flowchart for balancing chemical equations step by step
- Types of reactions with examples (visual classification chart)
Common Mistakes
- Writing "NA" for sodium instead of "Na" (capitalisation matters: NA is not an element)
- Changing subscripts to balance equations (only coefficients should be changed)
- Not simplifying subscripts after criss-cross (e.g., Ca2O2 should be CaO)
- Forgetting to write state symbols when asked for a complete equation
- Confusing variable valency metals (Fe can be 2 or 3, Cu can be 1 or 2)
Scoring Tips
- Memorise Latin-origin symbols: Na (Natrium), K (Kalium), Fe (Ferrum), Cu (Cuprum), Ag (Argentum), Au (Aurum), Hg (Hydrargyrum), Pb (Plumbum), Sn (Stannum)
- Always check atom count on both sides after balancing
- Learn valencies of common radicals as a table - this saves time
- Practice balancing at least 20 equations before the exam
Frequently Asked Questions
Why must chemical equations be balanced?
According to the Law of Conservation of Mass, matter can neither be created nor destroyed in a chemical reaction. A balanced equation ensures that the same number of atoms of each element appears on both sides, reflecting this law.
What is the difference between a coefficient and a subscript?
A coefficient is the number placed before a formula (e.g., 2H2O means 2 molecules of water). A subscript is the small number after an element symbol within a formula (e.g., H2O has subscript 2 for H). You can change coefficients to balance equations but never change subscripts.
Why do some elements have symbols that don't match their English names?
These symbols come from Latin or Greek names. For example, Na comes from "Natrium" (Latin for Sodium), K from "Kalium" (Latin for Potassium), and Au from "Aurum" (Latin for Gold). These names were established before English became dominant in science.