Question

A test tube containing molasses solution and yeast 8 be in a warm place overnight. The gas collected mixture (a) extinguishes the flame (b) bursts into flame when ignited (c) turns lime water milky (d) both (a) and (c).

Short answer

The gas collected (carbon dioxide) both extinguishes the flame (a) and turns lime water milky (c), thus the answer is option (d), both (a) and (c).

Step-by-step solution

Understanding the Fermentation Process

Recognize that yeast performs fermentation in the presence of sugar (like molasses) and absence of oxygen, producing carbon dioxide (CO2) and ethanol.

Predicting the Products' Reactions

Since carbon dioxide is one of the products of fermentation, this gas can be tested with two classic methods: (a) CO2 is a non-flammable gas that extinguishes flames. (c) CO2 can react with lime water (calcium hydroxide solution) to form calcium carbonate, which clouds the lime water.

Testing Against Options

Given that the gas collected is CO2, test it against (a) extinguishes the flame, and (c) turns lime water milky. CO2 does not support combustion, therefore it does not burst into flames, ruling out option (b).

Combining Correct Answers

Combine the outcomes which apply to CO2 - it extinguishes a flame and turns lime water milky. This leads to the conclusion that options (a) and (c) are correct.

Key concepts

Yeast Fermentation

Fermentation is a fascinating biological process that many of us benefit from regularly, whether it's through the bread we eat or the beverages we enjoy. At the heart of this process is yeast, a tiny microorganism with a mighty ability to convert sugars into alcohol and carbon dioxide (CO2). When yeast is added to a solution with sugar, like molasses, it begins to break down the sugar molecules in an anaerobic environment (i.e., without oxygen). This is not just a high school experiment but part of an age-old technique used in baking, brewing, and winemaking. Understanding yeast fermentation is crucial because it teaches us about the basic metabolic pathways that organisms use to generate energy. For students, dissecting this process aids in grasping concepts in biology, chemistry, and even food science.

Moreover, this experiment serves to connect theoretical knowledge with practical experiences, as observing the fermentation visually or by testing its byproducts, like CO2, cements the theoretical understanding. Incorporating multimedia visual aids, such as videos or animations, could enhance the student’s ability to visualize and comprehend the fermentation process. Additionally, suggesting activities like baking bread could contextualize the chemical reaction's outcomes in an everyday setting.

Carbon Dioxide Production

Understanding the production of CO2 is not only important in the context of yeast fermentation but also in broader scientific discussions like respiration and the carbon cycle. During yeast fermentation, carbon dioxide is produced as a waste product and is responsible for the bubbles commonly seen in fermenting solutions. In the context of the exercise, CO2 production can be identified and tested using simple experiments, such as the one involving molasses and yeast. The CO2 gas produced in such an experiment can be captured and tested for its unique properties.

This production of carbon dioxide also has practical applications. For instance, in bread making, the CO2 released by the fermenting yeast helps the dough to rise by creating air pockets. In an educational setting, it's valuable for students to perform experiments that demonstrate CO2 production, as these can solidify their understanding of gaseous byproducts in fermentation. An improvement to the exercise could involve having students measure the rate of carbon dioxide production under different conditions to explore kinetic concepts and the variables affecting fermentation.

Chemical Properties of CO2

Carbon dioxide is a colorless and odorless gas at room temperature. It has several distinctive chemical properties that make it suitable for a variety of tests. For example, CO2 is denser than air, enabling it to be collected easily over water in the fermentation experiment. Additionally, its acidity when dissolved in water is what allows it to turn lime water, which is a solution of calcium hydroxide, milky due to the formation of calcium carbonate. This is a visual clue often used in schools to demonstrate the presence of carbon dioxide.

When it comes to the flammability of CO2, it's important to note that it does not support combustion. This is why in the given exercise, CO2 extinguishes a flame rather than causing it to burst into flames. Educators can highlight these properties not only to guide students in predicting the outcomes of similar experiments but also to discuss the role of CO2 in fire extinguishers or its impact on ocean acidity. Using these properties to solve practical problems can help in devising improved experiments that emphasize the real-world importance of understanding CO2's chemical behavior.