ATDH - Admission Test for Dental Hygiene General Chemistry Principles Questions and Answers — 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?
- pH = 10; Remineralizing
- pH = 4; Demineralizing (Correct answer)
- pH = 4; Remineralizing
- pH = 10; Demineralizing
Correct answer: pH = 4; Demineralizing
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?
- Covalent bond
- Hydrogen bond
- Metallic bond
- Ionic bond (Correct answer)
Correct answer: Ionic bond
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)
- 5.84 g (Correct answer)
- 11.69 g
- 29.22 g
- 0.10 g
Correct answer: 5.84 g
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?
- Carbon-14 has two more protons than Carbon-12.
- Carbon-14 has two more electrons than Carbon-12.
- Carbon-14 has two more neutrons than Carbon-12. (Correct answer)
- Carbon-14 has two fewer protons than Carbon-12.
Correct answer: Carbon-14 has two more neutrons than Carbon-12.
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?
- The oxygen atoms are simultaneously oxidized and reduced. (Correct answer)
- The oxygen atoms only undergo oxidation.
- The oxygen atoms only undergo reduction.
- The oxygen atoms are transferred but their oxidation state is unchanged.
Correct answer: The oxygen atoms are simultaneously oxidized and reduced.
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.
Question 6: A reversible hydrocolloid impression material is heated to become a liquid and then cooled in a tray to become a semisolid gel in the patient's mouth. The physical process of changing from a liquid state to a solid state is called:
- Sublimation
- Condensation
- Solidification (or Freezing) (Correct answer)
- Evaporation
Correct answer: Solidification (or Freezing)
Solidification, also commonly known as freezing, is the phase transition in which a substance changes from a liquid to a solid. Sublimation is solid to gas, condensation is gas to liquid, and evaporation is liquid to gas.
ATDH - Admission Test for Dental Hygiene General Chemistry Principles Questions and Answers
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?