Experimental Design Practice Test

A lab group investigated whether a caffeine solution increases heart rate in Daphnia (water fleas). Hypothesis: higher caffeine concentration increases Daphnia heart rate. Procedure: (1) Prepare caffeine solutions at 0.0% (control), 0.1%, and 0.5% (mass/volume) in pond water. (2) Place one Daphnia in a depression slide with 1 mL of solution and allow 2 minutes to acclimate. (3) Under a microscope, count heartbeats for 15 seconds and multiply by 4 to estimate beats/min. (4) Repeat for 10 Daphnia per concentration. (5) The same student performed all counts to reduce observer variation. The group compared mean beats/min among concentrations.

A flaw in the experimental design is that:

A chemistry class tested whether the surface area of calcium carbonate affects reaction rate with hydrochloric acid. Hypothesis: powdered CaCO$_3$ reacts faster than a single large chunk of the same mass. Procedure: (1) Measure 2.00 g of CaCO$_3$ as either powder or one intact chip. (2) Add 50.0 mL of 1.0 M HCl to a 250 mL flask. (3) Add CaCO$_3$, immediately seal the flask with a stopper connected to a gas syringe, and start a timer. (4) Record CO$_2$ volume in the syringe every 10 s for 120 s. (5) Repeat 3 trials per CaCO$_3$ form, using fresh acid each time. The class compared CO$_2$ volume vs. time curves.

Which hypothesis is being tested?