Question 1: Explain what a metal hydroxide is and how it is formed.

Answer: A metal hydroxide is a compound formed when a metal reacts with water or hydroxide ions, resulting in a substance that contains the hydroxide ion (OH⁻). It is typically formed when metals such as aluminum or magnesium react with water or during neutralization reactions involving metal oxides and acids.

Question 1: Describe two physical properties commonly observed in metal hydroxides.

Answer: Metal hydroxides are usually solid substances that are often insoluble or sparingly soluble in water and tend to have a slippery or soapy texture.

Question 2: Which color is typical of aluminum hydroxide in a solution?

Answer: White

Question 1: What is the expected pH range of a solution containing a typical metal hydroxide?

Answer: The pH range is usually between 8 and 12, indicating a basic solution.

Question 2: Describe the result when a metal hydroxide solution reacts with an acid in a neutralization reaction.

Answer: When a metal hydroxide reacts with an acid, it produces a salt and water. This neutralization results in a decrease in pH towards neutral (around 7). For example, aluminum hydroxide reacting with hydrochloric acid produces aluminum chloride and water.

Question 1: Calculate the number of moles of magnesium hydroxide (Mg(OH)₂) in 0.5 grams of the compound. (Atomic masses: Mg = 24.3 g/mol, O = 16 g/mol, H = 1 g/mol)

Answer: Number of moles = 0.5 g / molar mass of Mg(OH)₂. Molar mass of Mg(OH)₂ = 24.3 + 2(16 + 1) = 24.3 + 2(17) = 24.3 + 34 = 58.3 g/mol. Moles = 0.5 / 58.3 ≈ 0.00857 mol.

Question 1: List three safety precautions to observe when handling metal hydroxide solutions in the laboratory.

Answer: Wear safety goggles and gloves, handle solutions carefully to avoid spills, and work in a well-ventilated area or under a fume hood.

Question 2: Design a simple experiment to test for the presence of hydroxide ions in a solution. Include the variables involved.

Answer: Add a few drops of the solution to a litmus paper or pH indicator. If the solution is basic, the litmus paper turns blue, indicating the presence of hydroxide ions. The independent variable is the solution tested; the dependent variable is the color change; the control is distilled water.

Question 1: A solution tested with a pH meter shows a pH of 10.5. What does this suggest about the solution's composition?

Answer: It suggests that the solution contains a basic substance, likely a metal hydroxide, since pH 10.5 indicates alkalinity.

Question 2: A student observes that adding a solution of a metal hydroxide to hydrochloric acid produces a precipitate. What could be the identity of the precipitate if the hydroxide is aluminum hydroxide?

Answer: The precipitate is aluminum hydroxide, which is insoluble in water and forms as a gelatinous white solid.

Question 1: Name one industry or field where metal hydroxides are used and describe their role.

Answer: In water treatment plants, aluminum hydroxide is used to remove impurities and clarify water by causing contaminants to coagulate and settle.

Question 2: Explain how magnesium hydroxide is used in medicine and why it is effective.

Answer: Magnesium hydroxide is used as an antacid to neutralize excess stomach acid, providing relief from indigestion and heartburn. Its basic properties allow it to react with hydrochloric acid in the stomach, forming magnesium chloride and water, thereby reducing acidity.