O levels Chemistry CAQ

Note: In Pure Chemistry, most questions are based on table and diagram analysis, whereas the following are concept-based questions. Chapter 1 Experimental Chemistry Q: Name the method to collect ammonia gas [1]- Upwards delivery method Q: Name the method to collect Chlorine gas [1]- Downward delivery method Q: Name the method to collect hydrogen gas [1]- Water displacement method Q: Suggest a method to separate iron filings from sand [1]- Magnetic attraction Q: Suggest how pure copper(II) sulfate crystals can be obtained from its solution [3]- Gently heat the solution until the solution becomes saturated . Cool the solution and Copper(ii) sulfate crystals will form . Filter the saturated solution , and copper(ii) sulfate crystals are obtained as residue . Wash the copper(ii) sulfate crystals with little distilled water and dry it on sheets of filter paper . Q: How to separate oil from water . [1]-

Using a separating funnel. Since water is denser , it will be on the bottom , while oil is at the top . Q: How to identify colourless substances in a chromatography test . [1]- Use Ultraviolet light and locating agents Q: suggest the purpose of boiling chips in fractional distillation. [1] - To ensure smooth and even heating Q: Describe how the chromatography of a pure substance will look like . [1] One dot on the chromatogram . Chapter 2 Kinetic particle theory Q: Describe the movement and arrangement of a solid . [3]- Particles of a solid are arranged in a very closely packed and orderly manner. Particles can only vibrate about their fixed positions . Q: Describe the movement and arrangement of a liquid. [3]- Particles of a liquid are arranged in a closely packed and disorderly manner . Particles can slide past each other . Q: Describe the movement and arrangement of a gas. [3]- Particles of a gas are far apart and disorderly . Particles of gas move around freely and randomly in all directions .

Q: Describe the change in movement and arrangement when a substance changes from solid to liquid state. [4]- As temperature increases , particles gain more kinetic energy and vibrate faster about their fixed positions , eventually , the particles with increased kinetic energy overcome the strong forces of attraction and change to liquid state . Movement of particles change from vibrating about their fixed position to being able to slide past each other . Arrangement of particles also changed from orderly and very close arrangement to disorderly and close arrangement . Q: Describe the change in movement and arrangement when a substance changes from liquid to gas state. [4]- As temperature increases , the particles gain more kinetic energy and eventually overcome the strong forces of attraction between particles . Causing the movement of particles to change from sliding past each other to being able to move quickly and randomly in all directions . The arrangement of particles also changes from close and disorderly arrangement to far apart and disorderly arrangement . Q: Describe the change in movement and arrangement when a substance changes from gaseous to liquid state. [4]- As temperature decreases , particles have less energy and are drawn closer together by the forces of attraction . Particles movement changed from moving quickly and randomly in all directions to being able to slide past each other . Arrangement of particles also changed from far apart and disordered arrangement to closer apart and disordered arrangement . Q: Describe the change in movement and arrangement when a substance changes from liquid to solid state. [4]-

As temperature decreases , particles have less energy and are drawn closer together by the forces of attraction , eventually changing to solid state . The particles' movement changed from sliding past each other to being able to only vibrate about their fixed positions . The arrangement of particles also changes from disordered and close arrangement to ordered and very close arrangement . Q: Define diffusion . [1]- Net movement of particles from a region of higher concentration to a region of lower concentration , down a concentration gradient. Q: Explain why ammonia diffuses faster than chlorine gas. [2]- Since ammonia gas is lighter than chlorine gas , it requires less kinetic energy to move around and thus ammonia gas diffuses faster than chlorine gas at the same temperature . Chapter 3 Atomic structure Q: Define atoms . [1]- Atoms are basic building blocks of matter . Q: Define isotopes [2]- Isotopes are atoms with the same number of protons but different number of neutrons . Q: Explain why isotopes have similar chemical properties , while different physical properties .[3]- Since isotopes have the same number of electrons and electrons shells , they have similar chemical properties . However , since isotopes are different in atomic mass , they have different physical properties .

Q: Define Metallic bond . [1]- Electrostatic forces of attraction between the positive ions and the sea of delocalised electrons in a metal . Chapter 4 and 5 Q: Describe the differences between mixtures and compounds. [3]- Mixtures do not have fixed ratios of its constituent , but compounds have fixed ratios of its constituent . Mixtures do have similar properties from its constituent elements , while compounds do not have similar properties from its constituent elements . Mixtures have boiling and melting points over a range of temperatures , while compounds have fixed boiling and melting points . Q: Explain why alloys tend to be less malleable and less ductile than pure metals .[2]- Since alloys are made of atoms of different sizes , causing the regular lattice arrangement to be disrupted , thus larger force is needed to make the layers slide past each other . Q: Explain why diamond is more hard than graphite , in terms of structure and bonding . [4] In diamond , each carbon atom is covalently bonded to 4 other carbon atoms in tetrahedral arrangement, thus it has a strong covalent bond . While for graphite , it has a layered structure made up of flat hexagons , where each carbon atom is covalently bonded to 3 other carbon atoms . The intermolecular forces of attraction are weak and the layers can slide past each other easily .

Q: Suggest and explain 1 physical property which graphite and diamond differ in .