Question

13. When a bit of baking soda is added to vinegar in a test-tube, a hissing
sound is heard and several bubbles occur. The test tube is closed and
attached by a glass tube to another test tube containing lime water. The
limewater slowly turns milky in the process. Which of the following
CANNOT be considered indicators of a chemical reaction in this
experiment?
a. Occurrence of a hissing sound.
b. The formation of several bubbles.
c. The movement of gas between the test tubes.
d. The change in color of liquid in tube 2.
​

Answer 1

Occurence of hissing sound is not an indicator of chemical change.

Answer 2

The phenomenon that is not an indicator or a chemical reaction is Option (c) The movement of gas between the test tubes.

EXPLANATION

• A chemical reaction is a phenomenon when two or more substances are converted into a different substance.
• A chemical reaction is indicated through various indicators such as, change of color, production of odor, change of temperature, etc.
• When baking soda is added to vinegar following reaction takes place

NaHCO₃ + CH₃COOH + CO₂ + H₂O

• The formation of Bubbles in the solution is evidence that a gas is produced.
• And, the Evolution of gas is indicated by the hissing sound.
• Therefore, Options (a) and (b) are indicators of chemical change.
• In the given experiment, the movement of gas cannot be considered an indicator of a chemical because the movement of gas (fluid) is a physical process and not a chemical process.
• A chemical change is said to occur only when there is the formation of a new product.
• When CO₂ reacts with lime water following reaction takes place -

CO₂ + Ca(OH)₂ --------> CaCO₃ + H₂O

• The color of the solution turns milky white due to the formation of a new product (Calcium carbonate).
• Therefore, the Change of color in test tube 2 is an indicator of chemical change.

Hence, The correct option is option (c) the occurrence of gas between the test tube.

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