Using a closed system experiment will a leak during gas evolving reaction overstate or understate the amount of sodium bicarbonate in an alka seltzer cold tablet?

It should be obvious that if some CO2 leaks out the amount of CO2 measured will be less so it will be understated. What is it about this problem you don't understand.

But is it an understate in Sodium Bicarbonate not CO2?

Too little CO2 means too little NaHCO3.

In a closed system experiment, any leak during a gas evolving reaction could potentially affect the accuracy of measuring the amount of sodium bicarbonate in an Alka-Seltzer Cold tablet. However, the specific impact on the measurement would depend on the nature and magnitude of the leak.

If there is a leak in the closed system, it would allow some gas (and possibly other substances) to escape into the surroundings. This means that not all of the gas produced as a result of the reaction between the sodium bicarbonate and water would be captured and measured accurately.

In such a scenario, the measured amount of gas evolved would be lower than the actual amount, resulting in an understatement of the quantity of sodium bicarbonate present in the Alka-Seltzer Cold tablet. The extent of this underestimation would depend on the rate and volume of gas escaping through the leak.

To mitigate the potential impact of a leak, it is essential to create as close to a completely sealed system as possible during the experiment. Ensuring proper sealing of the apparatus, using appropriate techniques like clamps and stoppers, and minimizing any potential points of leakage can help in obtaining more accurate results.