These eight questions are original and ramp from reading a symbol to judging a table. Write your answer first, then open the model answer.
Use the timed original practice session builder to try them against the clock. The lessons are in elements and materials.
Questions 1 to 4: atoms, categories and isotopes
Question 1. For ²³₁₁Na, state the number of protons, neutrons and electrons in a neutral atom, and its electron arrangement.
Answer
Protons = 11. Neutrons = 23 − 11 = 12. Electrons = 11.
Electron arrangement: 2.8.1. Check: 2 + 8 + 1 = 11.
Question 2. Classify each as element, compound or mixture: (a) nitrogen gas, (b) sodium chloride, (c) brass.
Answer
(a) Element: only nitrogen atoms.
(b) Compound: sodium and chlorine chemically joined in a fixed ratio of 1 : 1.
(c) Mixture: copper and zinc combined with no fixed ratio.
Question 3. A student adds 8 g of copper powder to 5 g of sulfur powder and stirs. Is the result a compound? Give a reason.
Answer
No, it is a mixture. Stirring does not join atoms chemically. The two powders keep their own properties and can be separated by physical means.
Question 4. Magnesium has isotopes ²⁴₁₂Mg and ²⁶₁₂Mg. State the difference in neutron number and explain why both react in the same way.
Answer
²⁴₁₂Mg has 12 neutrons and ²⁶₁₂Mg has 14 neutrons, so they differ by 2 neutrons.
They react alike because both have 12 electrons and the same electron arrangement, 2.8.2.
Questions 5 to 8: uses and classification
Question 5. State one property that makes a radioactive isotope useful for tracing a leak in a buried pipe.
Answer
It gives out radiation that a detector above ground can pick up, so the position of the leak can be found without digging the whole pipe.
Question 6. A table gives: material V melts at 1 410 °C, does not conduct as a solid or molten and is hard. State what the data suggests and what is missing.
Answer
The high melting point and the lack of conduction in any state suggest a giant covalent substance. The table does not give its appearance or whether it dissolves, which would support the classification.
Question 7. Material W melts at 62 °C and does not conduct when solid or liquid. Material X melts at 714 °C, does not conduct as a solid, and conducts when molten. Classify W and X.
Answer
W is a simple covalent substance, because of its low melting point and no conduction.
X is an ionic compound, because it has a high melting point and conducts only when molten, when its ions move.
Question 8. A student writes, “X is ionic because it is an ionic compound.” Rewrite the reason so it earns marks, using the data in Question 7.
Answer
“X has a high melting point of 714 °C and conducts when molten but not as a solid. This shows it contains ions that are fixed in the solid and free to move when molten.”
If you got these wrong, where do you go next?
Questions 1 and 4 point to reading atomic structure information and explaining isotopes. Questions 2 and 3 point to comparing elements, compounds and mixtures.
Questions 6 to 8 point to classifying materials from properties. For a teacher to read your answers, see online one-to-one Science tuition.