The elements shown are gases at room temperature and pressure.
hydrogen
nitrogen
oxygen
chlorine
(a) State which one of these gases is green.
(b) The gases shown exist as diatomic molecules. State the name of another element which has diatomic molecules and is a gas at room temperature and pressure.
(c) When separate samples of each of these gases are placed in a container they will diffuse.
(i) Describe why these gases diffuse.
(ii) State which of these four gases has the highest rate of diffusion.
Explain your answer.
(d) Nitrogen, oxygen and other substances are found in clean, dry air.
(i) State the percentage of nitrogen in clean, dry air.
(ii) Other than nitrogen and oxygen, identify another element found in clean, dry air.
(iii) Identify a compound found in clean, dry air.
(iv) Nitrogen and oxygen can be separated from liquid air. State the name of this process.
▶️ Answer/Explanation
(a) Ans: chlorine
Chlorine gas has a distinct greenish-yellow color, making it easily identifiable among the given options.
(b) Ans: fluorine
Fluorine is another diatomic element (F₂) that exists as a gas at room temperature, similar to the given examples.
(c)
(i) Gases diffuse due to the random motion of their particles, which causes them to spread out and mix.
(ii) Hydrogen diffuses fastest because it has the lowest molecular mass (2 g/mol), and diffusion rate is inversely proportional to the square root of molecular mass (Graham’s Law).
(d)
(i) Nitrogen constitutes 78% of clean, dry air.
(ii) Argon is another noble gas present in air (~1%).
(iii) Carbon dioxide (CO₂) is a compound found in trace amounts in air.
(iv) The separation process is called fractional distillation, which exploits different boiling points of liquid air components.
This question is about solids, liquids and gases.
(a) The list gives the names of nine substances which are solids at room temperature.
a ceramic
aluminum
anhydrous cobalt(II) chloride
anhydrous copper(II) sulfate
calcium oxide
graphite
iodine
iron
sodium
Answer the following questions about these substances.
Each substance may be used once, more than once or not at all.
State which substance:
(i) turns pink when water is added to it
(ii) is a non-metal which is used as a lubricant
(iii) is used to neutralize acidic industrial waste
(iv) is extracted from bauxite
(v) is used as an electrical insulator.
(b) Some changes of state of sodium are shown.
(i) State the names of the changes of state represented by A and B.
(ii) Use the kinetic particle model to describe the arrangement and separation of the particles in:
solid sodium
liquid sodium
▶️ Answer/Explanation
(a)
(i) Anhydrous cobalt(II) chloride turns pink when water is added due to the formation of hydrated cobalt(II) chloride.
(ii) Graphite is a non-metal with layered structure, making it an effective lubricant.
(iii) Calcium oxide neutralizes acidic waste as it is a basic oxide that reacts with acids.
(iv) Aluminum is extracted from bauxite ore through the Bayer process.
(v) Ceramic is used as an electrical insulator due to its high resistivity.
(b)(i)
A: Melting (solid to liquid)
B: Condensation (gas to liquid)
(b)(ii)
Solid sodium: Particles are closely packed in a regular arrangement with minimal movement.
Liquid sodium: Particles are close but disordered, allowing flow while maintaining proximity.