Answer:
In the investigation to determine if the time taken for magnesium to react completely with hydrochloric acid is affected by the concentration of the acid, it would be more suitable to use magnesium ribbon than powdered magnesium.
This is because magnesium ribbon has a larger surface area-to-volume ratio compared to powdered magnesium. The surface area of the magnesium ribbon is only on the outside, while the powdered magnesium has a much larger surface area due to its many small particles. A larger surface area-to-volume ratio means that there are more sites for the hydrochloric acid to react with the magnesium. This would result in a more rapid reaction between the magnesium and the acid, making it difficult to accurately measure the time taken for the reaction to complete.
Using magnesium ribbon, on the other hand, would minimize the effect of the surface area of the magnesium on the rate of reaction. The ribbon has a more consistent and smaller surface area-to-volume ratio, which would allow for a more accurate measurement of the time taken for the reaction to complete. Therefore, using magnesium ribbon would be more appropriate for this experiment.