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Q: Describe how to make pure, dry crystals of copper sulfate from copper oxide and sulfuric acid. A:
Warm sulfuric acid. Add excess copper oxide until no more reacts. Filter to remove excess solid. Evaporate solution to crystallise. (Marks for naming acid and base, adding excess, filtration, evaporation, crystallisation.)
Q: Why did Mendeleev leave gaps in his periodic table?
: For undiscovered elements.
How did arranging by atomic number solve the problems in Mendeleev’s table?
Put elements in correct groups with similar properties, fixed anomalies from atomic mass order.
Explain why diamond is hard.
: Each carbon makes four covalent bonds, forming a giant covalent structure with no weak forces.
Explain why graphite conducts electricity.
Each carbon bonds to three others, leaving delocalised electrons that move through the structure.
Why is graphite soft?
Weak forces between layers allow them to slide.
Describe the energy change in an exothermic reaction.
Energy is transferred to surroundings, temperature increases, products have less energy than reactants.
: What does the activation energy represent on a reaction profile?
Minimum energy needed for particles to react, shown as peak minus reactants.
: Why do elements in the same group have similar properties?
Same number of electrons in outer shell.
: Why does reactivity increase down Group 1?
Outer electron is further from nucleus, less attraction, easier to lose.
Why does reactivity decrease down Group 7?
Harder to gain an electron as outer shell is further from nucleus.
Why do ionic compounds have high melting points?
A: Strong electrostatic forces between oppositely charged ions in a giant lattice, lots of energy needed to break.
Why do ionic compounds conduct electricity when molten but not solid?
Ions are free to move when molten, fixed in place when solid.
Why do simple covalent molecules have low melting points?
Weak intermolecular forces between molecules, little energy needed to overcome
Why do metals conduct electricity?
: Delocalised electrons move freely through structure, carrying charge.
How are electrons arranged in shells?
: 2, 8, 8 (for first 20 elements).
Q: What is the equation for number of moles?
: Moles = mass ÷ Mr.
Why must the electrolyte be molten or in solution?
: Ions need to be free to move.
: What happens at the cathode in electrolysis of molten ionic compounds?
Positive ions gain electrons (reduction).
: What happens at the anode?
Negative ions lose electrons (oxidation).
: What is a displacement reaction?
A more reactive element displaces a less reactive element from a compound.
: Why does magnesium displace copper from copper sulfate?
: Magnesium is more reactive, so it forms magnesium sulfate and copper.
Why do simple molecular substances not conduct electricity?
No delocalised electrons or ions.
: What is bond energy?
Energy needed to break one mole of bonds.