Mouthwash used to reduce plaque and clean gums and teeth contains several such ingredients: menthol, alcohol, hydrogen peroxide, and flavoring. Is this a homogeneous or heterogeneous mixture? Classify each of the following as a physical or chemical change: – Rolled ingot hammered into gold leaf – Gasoline burns – Garlic chopped into small pieces – Milk left in warm room turns sour – Water freezes on pond – Gas bubbles form when baking powder is placed in vinegar – Cut firewood – Butter melts in a warm room A dermatologist uses cryogenic nitrogen at -196 °C to remove skin lesions and some skin cancers. What is the temperature, in degrees Fahrenheit, of the nitrogen? In the process of making ice cream, rock salt is added to crushed ice to chill the ice cream mixture. If the temperature drops to -11 °C, what is it in degrees Fahrenheit?
The Correct Answer and Explanation is:
Mouthwash Mixture Classification:
The mouthwash containing menthol, alcohol, hydrogen peroxide, and flavoring is a homogeneous mixture. This is because the ingredients are uniformly distributed throughout the solution, creating a consistent appearance and composition. Despite containing different substances, these components are thoroughly dissolved or suspended in the liquid, so it behaves like a single phase.
Classification of Changes:
- Rolled ingot hammered into gold leaf: This is a physical change. The shape of the gold changes, but its chemical composition remains the same.
- Gasoline burns: This is a chemical change. Combustion is a chemical reaction, resulting in the formation of new substances (e.g., carbon dioxide and water).
- Garlic chopped into small pieces: This is a physical change. The garlic’s size and shape change, but its chemical composition stays the same.
- Milk left in a warm room turns sour: This is a chemical change. The souring of milk involves a chemical reaction, where bacteria convert lactose into lactic acid.
- Water freezes on pond: This is a physical change. Water changes from liquid to solid (ice), but its chemical composition (H2O) remains unchanged.
- Gas bubbles form when baking powder is placed in vinegar: This is a chemical change. The reaction between baking powder and vinegar produces gas bubbles as new substances are formed.
- Cut firewood: This is a physical change. The wood is cut into smaller pieces, but no chemical transformation occurs.
- Butter melts in a warm room: This is a physical change. Butter changes from solid to liquid state, but its chemical structure remains unchanged.
Cryogenic Nitrogen Temperature Conversion:
The temperature of cryogenic nitrogen is -196°C. To convert this to Fahrenheit, use the formula:F=(95×C)+32F = \left(\frac{9}{5} \times C \right) + 32F=(59×C)+32
Substituting -196°C:F=(95×−196)+32=−320.8+32=−288.8°FF = \left(\frac{9}{5} \times -196 \right) + 32 = -320.8 + 32 = -288.8°FF=(59×−196)+32=−320.8+32=−288.8°F
So, the temperature of the nitrogen is -288.8°F.
Rock Salt and Ice Temperature Conversion:
The temperature of the ice cream mixture is -11°C. To convert to Fahrenheit:F=(95×−11)+32=−19.8+32=12.2°FF = \left(\frac{9}{5} \times -11 \right) + 32 = -19.8 + 32 = 12.2°FF=(59×−11)+32=−19.8+32=12.2°F
So, the temperature is 12.2°F.
Summary:
- Mouthwash is a homogeneous mixture.
- The changes: some are physical, others are chemical, based on whether the composition of substances is altered.
- Cryogenic nitrogen is -288.8°F, and ice cream mixture is 12.2°F.
