Question

final examination
time allowed – 1 hour & 30 minutes 200 marks
physical science and earth and space science
chemistry

1. air is composed of nitrogen, oxygen, argon, carbon dioxide, and other gases.

how may air be best described?
a. a compound
b. a mixture
c. a solution
d. an alloy

1. iron (fe) can combine with oxygen (o) to produce any one of the three different iron oxides. feo,

fe₂o₃, and fe₃o₄. of the three oxides, feo is the most unstable. if feo is exposed to air, it forms
fe₂o₃. which equation correctly describes this reaction?
a. feo + o₂ → fe₂o₃
b. feo + o₂ → 2fe₂o₃
c. 2feo + o₂ → fe₂o₃
d. 4feo + o₂ → 2fe₂o₃

1. if heat is added to a liquid which of the following occurs?

a. the viscosity of liquid increases
b. the size of liquid molecules expands
c. the molecular motion in the liquid increases
d. the state of liquid changes to solid

1. water is a polar substance. it is called so because:

a. its molecules have positive and negative poles on either side due to a difference in the valency of
hydrogen and oxygen.
b. it is composed of more than one element.
c. water is amphoteric; it is neither basic nor acidic.
d. water has extremely weak intermolecular forces.
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1. which of the following types of chemical bonds is very strong and involves transfer of an electron

between atoms?
a. covalent bonds
b. ionic bonds
c. hydrogen bonds
d. disulfide bonds

1. during a chemical reaction, the reactants are changed into the products. the following graph shows the

potential energy stored in the chemical bonds at various stages of the reaction.
which of the following statements correctly interprets the graph?
potential
energy
activation
energy

Explanation:

Question 1

Air has nitrogen, oxygen, argon, etc., mixed without chemical bonding. A compound has fixed composition, a solution is a homogeneous mixture (air is gaseous mixture), alloy is metal mixture. So air is a mixture.

Step1: Balance Fe and O. Reactant FeO, product \(Fe_2O_3\).

Step2: For Fe: 4 FeO gives 2 \(Fe_2O_3\) (4 Fe on left, 4 on right). For O: 4 FeO has 4 O, \(O_2\) has 2 O, total 6 O. Product \(2Fe_2O_3\) has 6 O. So equation \(4FeO + O_2

ightarrow 2Fe_2O_3\).

Adding heat to liquid increases molecular kinetic energy, so molecular motion increases. Viscosity decreases, molecules don't expand, liquid becomes gas (not solid).

Answer:

B. a mixture

Question 2