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DSE Chemistry: Microscopic World I — Practice Questions & Answers
Atomic structure, isotopes, the periodic table, and the three main models of bonding: ionic, covalent and metallic, with their structures and properties.
546 practice questions available for this topic — here are 10 with full answers and explanations.
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Practice questions with answers
1
Multiple choice · Easy
Which of the following substances CANNOT conduct electricity?
CH3CH2OH(l)
PbBr2(l)
C(graphite)
Pt(s)
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Why CH3CH2OH(l) is a simple molecular liquid with no mobile ions or delocalised electrons.
2
Multiple choice · Medium
Which statement about the electrical conductivity of sodium chloride is correct?
It conducts when molten or in solution but not when solid
It conducts in all three states
It conducts only when solid
It never conducts because it is covalent
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Why Solid NaCl has ions fixed in the lattice; molten or aqueous NaCl has mobile ions that conduct.
3
Multiple choice · Medium
Graphite differs from diamond in that graphite can conduct electricity. This is because in graphite each carbon atom
has one delocalised electron not used in bonding
forms four single covalent bonds
carries a positive charge
is held only by van der Waals forces
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Why In graphite each C atom forms three bonds, leaving one delocalised electron per atom.
4
Fill in the blank · Medium
A metal conducts electricity in the solid state because of the presence of a sea of
Check answer
Answer:
delocalised / delocalized / mobile
Why These mobile electrons carry the current.
5
Fill in the blank · Medium
Molten lead(II) bromide conducts electricity because the
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Answer:
ions / mobile ions
Why This allows electrolysis to occur.
6
Fill in the blank · Easy
Ethanol is a simple molecular substance, so it cannot conduct electricity because it has no
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Answer:
mobile ions / free ions / ions
Why No mobile charged particles are present.
7
Multiple choice · Medium
In an oxide of metal M, the mass percentage of M is 55.0%. (Relative atomic masses: O = 16.0, M = 39.1.) What is the chemical formula of this oxide?
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Why n(M):n(O) = (55.0/39.1):(45.0/16.0) = 1:2, so MO2.
8
Multiple choice · Medium
3.2 g of copper (Ar = 64) combines with 0.8 g of oxygen (Ar = 16). What is the empirical formula of the oxide?
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Why n(Cu) = 0.05, n(O) = 0.05, ratio 1:1, so CuO.
9
Multiple choice · Easy
The empirical formula of a compound is defined as
the simplest whole-number ratio of atoms of each element
the exact number of atoms in one molecule
the relative molecular mass of the compound
the shape of the molecule
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Why It is the simplest integer ratio of atoms of the elements present.
10
Fill in the blank · Medium
A metal oxide contains 0.10 mol of K atoms and 0.05 mol of O atoms. Its empirical formula is
Check answer
Answer:
K2O
Why K:O ratio is 2:1.
Key terms in Microscopic World I
Atom: The smallest particle of an element that retains the chemical properties of that element.
Proton: A positively charged subatomic particle found in the nucleus with a relative mass of one.
Neutron: An electrically neutral subatomic particle in the nucleus with a relative mass of one.
Electron: A negatively charged subatomic particle of negligible mass that occupies shells around the nucleus.
Atomic number: The number of protons in the nucleus of an atom, which identifies the element.
Mass number: The total number of protons and neutrons in the nucleus of an atom.
Isotope: Atoms of the same element with the same number of protons but different numbers of neutrons.
Relative atomic mass: The weighted average mass of an element's atoms compared to one-twelfth of a carbon-12 atom.
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