Sample items “Atomic Theory and Chemical Bonding”

1- The type of attraction between the positive ions of the metal and the sea of the electrons in a metallic bonding is:

A) magnetic.

B) electrostatic.

C) electromagnetic.

D) ionic.

E) covalent.

The outer electrons within a metal are free to move and delocalize; the type of the metallic ion is a cation. As a result, an attraction among these opposite charges takes place which is known as a metallic bonding. It is not due to attraction among opposite poles of a magnet, and not among a metal and a nonmetal to be ionic and eventually it’s not the result of sharing among metals and nonmetals so not covalent.

2- Which electron configuration represents an atom in the excited state?

A) 1s² 2s² 2p³

B) 1s² 2s² 2p⁶

C) 1s² 2s¹ 2p¹

D) 1s² 2s² 2p⁶3s¹

E) 1s² 2s¹

An electron configuration representing an excited state is shown by a valence electron promoted to a higher energy level.

3- Refer to the following. Choose the best answer from the given list of possible choices.
The element forming a tetrahedral structure with sp³ hybrid orbital when bonded with the appropriate atoms of fluorine

A) Carbon

B) Nickel

C) Hydrogen

D) Neon

E) Potassium

The central atom has to be in group 4A to exhibit a tetrahedral geometry so it is Carbon.

Sample items “Chemical Behavior (aqueous solutions and gaseous state)”

4- What is the correct unit for molality?

A) moles/liter of solution

B) grams/mol

C) moles/kilogram of solvent

D) °C/molal

E) no unit

molality is the number of moles of solute per kilograms of solvent, m = moles of solute/kg of solvent.

5- What is the correct unit for molar mass?

A) moles/liter of solution

B) grams/mol

C) moles/kilogram of solvent

D) °C/molal

E) no unit

molar mass is the mass in grams of one mole of a substance → M = m/n with grams/mol unit.

6- Lead (II) sulfide (PbS) has a Ksp value of 3.0 x 10^-28. What is the concentration of lead (II) ions in a saturated solution of PbS at 25°C?

A) 1.5 x 10^-14 M

B) 1.7 x 10^-14 M

C) 16 x 10^-56 M

D) 6 x 10^-28 M

E) 1.7 x 10^-28 M

PbS ⇔ Pb²⁺ + S^2-
Ksp = [Pb²⁺] x [S^2-]
With [Pb²⁺] = [S^2-]
3.0 x 10^-28 = [Pb²⁺]²
[Pb²⁺] = 1.7 x 10^-14 M

7- The gas law describing this graph is:

A) Charles’s law.

B) Dalton’s law.

C) Boyle’s law.

D) Gay-Lusac’s law.

E) Avogadro’s law.

Boyle’s Law represents a relation between Pressure and Volume where these two parameters are inversely proportional and the curve is hyperbolic in nature. The curve represented indicates this information:

Sample items “Chemical Reactions”

8- Indicate the type of reaction of the following.
CH₃COOH + NH₃ → CH₃COO^– + NH₄⁺

A) precipitation reaction

B) acid base reaction

C) decomposition reaction

D) combustion reaction

E) double displacement reaction

No solid formed thus not (A).
A decomposition reaction is identified by the presence of one reactant thus not (C).
Combustion reaction produces water vapor besides carbon dioxide, or carbon monoxide thus not (D).
Double replacement reaction takes place between two ionic species which is not present here thus not (E).
Alternative B: It is a chemical reaction between a weak acid (donates hydrogen ions) and a weak base (accept hydrogen ions) → Acid base reaction.

9- A solution with [H⁺] = 3 x 10^-9 has a pH between:

A) 7 and 8

B) 4 and 5

C) 5 and 6

D) 8 and 9

E) None of the above.

pH = -log [H₃O⁺] = -log [3 x 10^-9] = 8.522

10- What are the oxidized and reduced elements in this unbalanced reaction?
MnO₄^– + SO₂ → Mn²⁺ + SO₄^2-

A) MnO₄^– and SO₂ respectively

B) Mn²⁺ and SO₄^2- respectively

C) SO₂ and MnO₄^– respectively

D) SO₂ and SO₄^2- respectively

E) MnO₄^– and Mn²⁺ respectively

Oxidation number of Mn is: 7 in MnO₄^– and 2 in Mn²⁺ ; this decrease in oxidation number verifies that MnO₄^– is reduced.
Oxidation number of S is: 4 in SO₂ and 6 in SO₄^2- this increase in oxidation number verifies that SO₂ is oxidized.

Sample items “Quantitative Chemistry”

11- The formula applied to calculate the percentage yield for a chemical reaction is:

A) (Actual amount of reactant / theoretical amount of reactant) x 100

B) (Actual amount of product / theoretical amount of reactant) x 100

C) (Actual volume of product / theoretical volume of product) x 100

D) (Actual amount of product / theoretical amount of product) x 100

E) (Actual mass of product / theoretical mass of product) x 100

It is a standard formula to be known.

12- What is the balancing coefficient of hydrogen fluoride in the following unbalanced chemical equation?
SiO₂ + HF → SiF₄ + 2H₂O

A) 1

B) 3

C) 4

D) 2

E) 6

In order to have conservation of mass and a balanced chemical equation; the balancing coefficient of HF should be 4 since 4 fluorine atoms are present in the product’s side as in SiF₄

13- How many moles of NaOH are needed to neutralize 1.6 mol of H₂SO₄?

A) 1.6 mol

B) 3.2 mol

C) 0.8 mol

D) 6.4 mol

E) 8 mol

A strong base reacts with a strong acid to produce salt and water. The equation of the chemical reaction taking place is:
2NaOH + H₂SO₄ → Na₂SO₄ + H₂O
n NaOH /2 = n H₂SO₄/1 (Stoichiometry)
n (NaOH) = 2 x n H2SO4 = 2 x 1.6 = 3.2 mol

Sample items “Periodic Table and Periodic Trends”

14- The name of the ionic compound having the formula unit (CuCl₂) is

A) copper chloride.

B) copper (II) chlorate.

C) cupric chromate.

D) copper (II) chloride.

E) copper (I) chlorine.

CuCl₂ is made up of a cation Cu²⁺ which is known as copper (II) and Cl^- which is known as chloride ion. Thus the right answer is part D.

15- Choose the element with the higher ionization energy.

A) S

B) P

C) Cd

D) Ta

E) K

Ionization energy is the highest as we move upward within a group and from left to right within a period. S is the right choice since, referring to the periodic table, it lies above all other elements mentioned.

16- The order of the following chemical elements Na,K,Rb,Cs represents:

A) increasing first ionization energy.

B) decreasing first ionization energy.

C) increasing electronegativity.

D) decreasing atomic radius.

E) random and lack of order of any periodic trend.

Na,K,Rb,Cs belong to the same group (group 1A)
The order given represents a decreasing first ionization energy since as we move within a group from top to bottom the first ionization energy decreases where it is easier for a valence electron to be removed as the size of the atom increases and the electrons turns to be farther from the nucleus.

Sample items “Chemical Kinetics and Chemical Equilibrium”

17- Which statement describes the characteristics of an endothermic reaction?

A) The sign of ΔH is positive, and the products have less potential energy than the reactants.

B) The sign of ΔH is positive, and the products have higher potential energy than the reactants.

C) The sign of ΔH is negative, and the products have less potential energy than the reactants.

D) The sign of ΔH is negative, and the products have higher potential energy than the reactants.

E) The sign of ΔH is positive.

In an endothermic reaction energy is absorbed as a result the potential energy of the products is higher than that of the reactants. As a result the difference among them is positive (ΔH > 0).

18- Which reaction is represented by the following expression of the equilibrium constant?
K_eq = [CO]² x [O]² / [CO₂]²

A) 2CO₂ ⇆ O₂ + 2CO

B) CO₂ ⇆ O₂ + 2CO

C) O₂ + 2CO ⇆ 2CO₂

D) O₂ + CO ⇆ CO₂

E) None of the above.

The equilibrium constant formula represents the ratio of the equilibrium concentrations of the products over those of the reactants; each raised to the power of their stoichiometric coefficients. Based on this, the given
K_eq corresponds to the equation in part (A).

19- What type of reaction is this?

A) athermic

B) exothermic

C) endothermic

D) reversible reaction

E) None of the above.

In an endothermic reaction, energy is absorbed. As a result, the potential energy of the product (z) is higher than that of the reactants (x + y).

Sample items “Experimental Chemistry”

20- The following setup below stands for:

A) Fractional distillation

B) Simple distillation

C) Titration setup

D) Synthesis reaction setup

E) None of the above.

Once a liquid is collected as shown in part (D) and a column known as a fractionating column is shown in part (B) by a heating as illustrated, then the experiment’s target is to separate components of a mixture which is fractional distillation.

21- Consider the following table:

Air pressure with increasing altitude
Altitude (in kilometers)	Air pressure (in kPa)
0	101
2	83
4	64
6	51
8	41
10	32

What does this data reveal about the relation between air pressure and altitude?

A) The data is insufficient.

B) There is no relation.

C) They are directly proportional.

D) They are inversely proportional.

E) As the air pressure increases, the altitude increases as well.

As the altitude increases, the air pressure decreases. This is clearly obvious upon analyzing and comparing the given values. This relation is inversely proportional.

22- In this experiment, a student will synthesize aspirin. The synthesis reaction is:
Salicylic acid + Acetic anhydride → Acetylsalicylic acid + acetic acid
C₇H₆O₃ + C₄H₆O₃ → C₉H₈O₄ + C₂H₄O₂

After heating the Erlenmeyer flask, the technician removed it from the water bath and let it cool down, then added 15 mL of room temperature distilled water. What was the reason for his actions?

A) to dilute the mixture

B) to increase the volume of the mixture

C) to let the mixture cool faster

D) to facilitate the decomposition of the excess acetic anhydride

E) A and C

Adding extra room temperature distilled water after heating allows any extra acetic anhydride to react with water producing acetic acid which is already a product in this reaction. This facilitates the process of the collection of aspirin.