Elements, Compounds, Mixtures, Separation
Classify each of the following as element, compound, or mixture: (i) Oxygen gas, (ii) Steel, (iii) Glucose
(i) Element, (ii) Mixture (alloy), (iii) Compound
Compare the behavior of particles in solids, liquids, and gases using kinetic theory principles.
Solids – particles vibrate; liquids – move freely but close; gases – high-speed random motion.
An atom has mass number 31 and atomic number 15. Give its full electronic configuration and name.
Phosphorus; 2,8,5
Balance: Al + O₂ → Al₂O₃
4Al + 3O₂ → 2Al₂O₃
Justify why alloys like brass are considered mixtures, not compounds.
Their composition can vary; components are not chemically bonded.
A gas is compressed in a syringe. Predict and explain the change in particle behavior and pressure.
Particles collide more often → pressure increases.
Identify which of the following pairs are isotopes:
A: ¹⁶O, ¹⁷O
B: ¹²C, ¹²N
Pair A are isotopes (same element, different neutrons)
State the type of bonding and structure in sodium chloride. Explain its melting point.
Ionic bonding; giant lattice; strong electrostatic forces → high melting point.
Describe a complete method to obtain pure copper sulfate crystals from a mixture of copper oxide and sulfuric acid
Add copper oxide to warm sulfuric acid → filter excess → evaporate water → crystallize.
A container of helium is heated. Predict and explain changes in particle speed and energy.
Both increase; KE ∝ Temperature (in Kelvin).
Explain how the number of valence electrons affects chemical reactivity across a period and down a group
Across a period: reactivity varies as elements approach noble gas configuration; Down a group: metals get more reactive, non-metals less reactive.
Draw dot-and-cross diagrams for MgCl₂ and CH₄. Highlight the difference in bonding.
MgCl₂ – ionic; CH₄ – covalent.
Design an investigation to separate and identify the components of black ink using chromatography.
Include setup, solvent selection, Rf value measurement, and color comparison to standards.
Why does a balloon burst when heated? Use kinetic theory and pressure concepts.
Particle speed increases → more frequent & forceful collisions → pressure exceeds limit → burst.
Explain how ionization energy is affected by nuclear charge and atomic radius.
Increases with higher nuclear charge; decreases with larger atomic radius due to weaker attraction.
Write the name and IUPAC formula for a compound made of ammonium and sulfate ions.
Ammonium sulfate – (NH₄)₂SO₄
A mixture contains salt, camphor, and iron filings. Design a step-by-step separation plan, identifying the physical property exploited in each step.
Use magnet (magnetism) → sublimation (camphor) → dissolve & filter (salt).
Derive and explain the relationship between pressure and temperature using kinetic theory (P ∝ T at constant volume).
As temperature rises, average KE increases, collisions become more forceful and frequent, increasing pressure.
Compare the structure and charge of a sodium atom and a sodium ion. Justify how this affects its reactivity.
Atom: 11e⁻, 1 valence; Ion: 10e⁻, stable shell → less reactive as ion.
NH₃+O₂→NO+H₂O
(a) Balance the equation.
(b) What type of reaction is this?
(a) 4NH₃ + 5O₂ → 4NO + 6H₂O
(b) This is a redox reaction (oxidation-reduction).