ATDH - Admission Test for Dental Hygiene Chemical Equations and Reactions Questions and Answers — Questions and Answers
Question 1: The process of teeth whitening often involves the decomposition of hydrogen peroxide (H₂O₂), which breaks down into water (H₂O) and oxygen gas (O₂). Which of the following correctly balances the chemical equation for this reaction?
- H₂O₂ → H₂O + O₂
- 2H₂O₂ → 2H₂O + O₂ (Correct answer)
- H₂O₂ → 2H₂O + O₂
- 2H₂O₂ → H₂O + 2O₂
Correct answer: 2H₂O₂ → 2H₂O + O₂
To balance the equation, the number of atoms of each element must be the same on both sides. The equation 2H₂O₂ → 2H₂O + O₂ has 4 hydrogen atoms and 4 oxygen atoms on the reactant side, and 4 hydrogen atoms and (2+2)=4 oxygen atoms on the product side, satisfying the Law of Conservation of Mass.
Question 2: A patient's saliva helps to neutralize acidic byproducts from plaque bacteria. The reaction of an acid (like HCl from stomach reflux) with a base (like NaOH) to produce a salt (NaCl) and water (H₂O) is a classic example of what type of chemical reaction?
- Decomposition
- Single Replacement
- Neutralization (Correct answer)
- Combustion
Correct answer: Neutralization
A neutralization reaction is a specific type of double replacement reaction where an acid and a base react to form a salt and water. This process is crucial in the oral cavity for counteracting acids that can lead to enamel erosion.
Question 3: The fundamental principle that requires the number of atoms of each element to be identical on both sides of a chemical equation is known as:
- The Law of Definite Proportions
- The Law of Multiple Proportions
- Avogadro's Law
- The Law of Conservation of Mass (Correct answer)
Correct answer: The Law of Conservation of Mass
The Law of Conservation of Mass states that mass in an isolated system is neither created nor destroyed by chemical reactions. Therefore, the mass of the reactants must equal the mass of the products, which is achieved by ensuring the same number of atoms for each element are present on both sides of the equation.
Question 4: In the mouth, salivary amylase is an enzyme that accelerates the breakdown of complex carbohydrates (starch) into simpler sugars. What is the role of salivary amylase in this chemical reaction?
- A catalyst (Correct answer)
- A reactant
- A product
- An inhibitor
Correct answer: A catalyst
Salivary amylase acts as a biological catalyst. A catalyst is a substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change. Enzymes are proteins that serve as catalysts in biological systems.
Question 5: Phosphoric acid (H₃PO₄) is used in dentistry to etch tooth enamel, while calcium hydroxide (Ca(OH)₂) can be used as a pulp-capping agent. Which of the following are the correct products of the neutralization reaction between these two compounds?
- Calcium phosphide and hydrogen gas
- Calcium phosphate and dihydrogen monoxide (Correct answer)
- Calcium perchlorate and water
- Calcium phosphite and hydrogen peroxide
Correct answer: Calcium phosphate and dihydrogen monoxide
This is a double replacement and neutralization reaction. The calcium (Ca²⁺) from the base combines with the phosphate (PO₄³⁻) from the acid to form the salt calcium phosphate (Ca₃(PO₄)₂). The hydrogen (H⁺) from the acid combines with the hydroxide (OH⁻) from the base to form water (H₂O), also known as dihydrogen monoxide. The balanced equation is 2H₃PO₄ + 3Ca(OH)₂ → Ca₃(PO₄)₂ + 6H₂O.
Question 6: Fluoride ions (F⁻) strengthen tooth enamel by reacting with hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) to form the more acid-resistant fluorapatite (Ca₁₀(PO₄)₆F₂). Based on the balanced reaction Ca₁₀(PO₄)₆(OH)₂ + 2F⁻ → Ca₁₀(PO₄)₆F₂ + 2OH⁻, what is the stoichiometric mole ratio of hydroxyapatite to fluoride ions?
- 10:2
- 1:1
- 1:2 (Correct answer)
- 2:1
Correct answer: 1:2
Stoichiometry involves the mole ratios of reactants and products, which are indicated by the coefficients in a balanced chemical equation. In this reaction, the coefficient for hydroxyapatite is an implied 1, and the coefficient for fluoride ions is 2. Therefore, the ratio is 1 mole of hydroxyapatite to 2 moles of fluoride ions.
ATDH - Admission Test for Dental Hygiene Chemical Equations and Reactions Questions and Answers
The process of teeth whitening often involves the decomposition of hydrogen peroxide (H₂O₂), which breaks down into water (H₂O) and oxygen gas (O₂).
Which of the following correctly balances the chemical equation for this reaction?