FAULTY EXPERIMENTS
Can you work out what the experimenter has done wrong in each of these experiments?
Experiment #1
John wants to see how long it takes for an acid to dissolve a piece of metal. He puts a piece of metal in some acid and times how long it takes to completely dissolve.
Metal in acid
Experiment #2
Mary wants to see if crushing up chalk makes it dissolve faster in acids and bases. She places a whole piece of chalk in acid, and the same chalk, crushed up, in a base. The crushed up piece of chalk dissolves faster. Mary concludes that chalk dissolves faster when crushed up, and bases dissolve chalk faster than acids.
Whole chalk with acid Powdered chalk with base
Experiment #3
Peter wants to see if temperature affects rusting. He places one nail in 50mL of normal water, and places another nail in 50mL of water that he cools to 0°C. He checks after two days and sees that the nail at room temperature has rusted more. (Clue: check the diagram).
Nail with water – room temperature Nail with water - 0°C
Experiment #4
Chen is investigating how different cola drinks dissolve pieces of chalk. He investigates three types of cola, and sets up his test by half filling the flasks as per the diagram. Chen finds cola B dissolves the chalk the best. (Clue: check the diagram)
Chalk in cola A Chalk in cola B Chalk in cola C
Experiment #5
Doug is interested in finding out how the pH of soil affects the growth of plants. He takes two tomato plants. He makes the soil of one neutral (pH 7). He makes the soil of the other acidic (pH less than 7). Doug places them on the same spot on a shelf. The plant with the neutral soil dies after eight days. The plant with the acidic soil dies after nine days. Doug concludes that acidic soil helps plants stay alive.
Plant A – neutral soil Plant B – acidic soil
Dies after eight days Dies after nine days
Experiment #6
Edwina wants to see if different colas will corrode coins. She weighs three identical coins and places them in three flasks. Edwina then adds 50mL of cola to one, 50mL of diet cola to another, and 50mL of tap water to the last one. She waits three days, then cleans the coins. She weighs each one using a balance. She reaches the following results:
Coin with tap water Lost 0.0015g
Coin with cola Lost 0.0016g
Coin with diet cola Lost 0.0021g
Edwina concludes that diet cola is more corrosive to coins than normal cola or water.
Coin in tap water Coin in cola Coin in diet cola
Experiment #7
Anna is investigating the corrosive effect of acetic acid on steel wool. She places a 15g piece of steel wool in a 100mL beaker and adds 50mL of water as a control. She then places another 15g piece of steel wool in a 100mL beaker and adds 50mL of acetic acid. She waits two days. Both pieces of steel wool appear rusted, but the one in the acetic acid appears more rusted. She tries it another two times and gets the same results.
Anna concludes that steel wool rusts more in acetic acid than in water.
15g with 50mL water 15g with 50mL acetic acid