ATDH - Admission Test for Dental Hygiene General Chemistry Principles Questions and Answers

Question 1

The critical pH for enamel demineralization is approximately 5.5. A patient consumes a beverage with a hydronium ion [H₃O⁺] concentration of 1.0 x 10⁻⁴ M. What is the pH of this beverage, and what is its likely effect on tooth enamel?

Accepted Answer

pH = 4; Demineralizing

Answer

The pH of a solution is calculated as the negative logarithm of the hydronium ion concentration (pH = -log[H₃O⁺]). For this beverage, pH = -log(1.0 x 10⁻⁴) = 4.0. Since a pH of 4.0 is more acidic than the critical pH of 5.5, it will cause the demineralization of tooth enamel.

Question 2

Sodium fluoride (NaF), a common ingredient in toothpaste, is formed when a sodium atom transfers a valence electron to a fluorine atom. What type of chemical bond is formed between the resulting sodium and fluoride particles?

Accepted Answer

Ionic bond

Answer

An ionic bond is formed by the electrostatic attraction between oppositely charged ions. In this case, sodium (Na) loses an electron to become a positive cation (Na⁺), and fluorine (F) gains that electron to become a negative anion (F⁻). The attraction between these two ions creates the ionic bond.

Question 3

A dental hygienist needs to prepare 500 mL of a 0.2 M saline solution (NaCl) for a patient rinse. How many grams of sodium chloride (NaCl) are required? (Molar mass of NaCl ≈ 58.44 g/mol)

Accepted Answer

5.84 g

Answer

To solve this, first calculate the number of moles needed using the formula: Moles = Molarity × Volume (in Liters). Convert 500 mL to 0.5 L. Moles = 0.2 mol/L × 0.5 L = 0.1 mol. Then, convert moles to grams: Grams = Moles × Molar Mass. Grams = 0.1 mol × 58.44 g/mol = 5.84 g.

Question 4

Carbon-12 and Carbon-14 are two isotopes of carbon. Which of the following statements correctly describes the difference between an atom of Carbon-14 and an atom of Carbon-12?

Accepted Answer

Carbon-14 has two more neutrons than Carbon-12.

Answer

Isotopes are atoms of the same element, meaning they have the same number of protons. The number of protons defines the element (Carbon always has 6 protons). The number following the element name (12 or 14) is the mass number (protons + neutrons). Therefore, Carbon-12 has 6 neutrons (12 - 6), and Carbon-14 has 8 neutrons (14 - 6), which is a difference of two neutrons.

Question 5

Hydrogen peroxide (H₂O₂) is used as a whitening agent because it decomposes into water (H₂O) and oxygen gas (O₂). This is a type of redox reaction known as a disproportionation reaction. What does this mean for the oxygen atoms in H₂O₂?

Accepted Answer

The oxygen atoms are simultaneously oxidized and reduced.

Answer

In H₂O₂, oxygen has an oxidation state of -1. In the product H₂O, oxygen's oxidation state becomes -2 (a reduction, gain of electrons). In the product O₂, its oxidation state becomes 0 (an oxidation, loss of electrons). Because the oxygen atoms from the same reactant are both oxidized and reduced, this is a disproportionation reaction.

ATDH - Admission Test for Dental Hygiene Practice Test

ATDH - Admission Test for Dental Hygiene Practice Test

ATDH - Admission Test for Dental Hygiene General Chemistry Principles Questions and Answers