Chemistry Practice Paper Review
Key recall facts and worked answers from the mixed chemistry practice paper.
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Questions Covered in This Set
11 cards to master
³⁵₁₇Cl — protons, neutrons, electrons?
17 protons, 18 neutrons (35 − 17), 17 electrons.
Why do elements in the same group behave similarly?
They have the same number of electrons in their outer shell.
Why does NaCl conduct when molten but not solid?
Solid ions are fixed in a lattice; when molten the ions are free to move and carry charge.
Balance: __Al + __O₂ → __Al₂O₃
4Al + 3O₂ → 2Al₂O₃
Mr of Ca(OH)₂ (Ca=40, O=16, H=1)?
40 + 2(16 + 1) = 74
Acid + metal carbonate →
Salt + water + carbon dioxide
Define a catalyst.
A substance that speeds up a reaction by providing an alternative pathway of lower activation energy, without being used up.
4.8 g Mg burned in oxygen — mass of MgO formed?
n = 4.8/24 = 0.20 mol; 2Mg + O₂ → 2MgO; 0.20 × 40 = 8.0 g MgO
Moles in 25 cm³ of 0.100 mol/dm³ HCl?
n = c × V = 0.100 × 0.025 = 0.00250 mol (and 0.00250 mol NaOH, 1:1)
Why does higher temperature increase rate?
Particles move faster → more frequent collisions and a greater proportion exceed the activation energy.
Why is diamond hard but graphite soft?
Diamond: each C bonded to 4 others in a rigid giant covalent lattice. Graphite: layers of C bonded to 3 others with weak forces between layers that slide.
