Whose Computer Tablet It is? 

You were walking through the shopping mall and you found a computer tablet.  It doesn’t have any identification and is locked so you can’t figure out to whom it belongs.  However, you notice several smudges of white powder on the keyboard which you can scrap off for identification. You post a lost-and-found poster to try to return it to its owner; unfortunately, five different people claim the tablet belongs to them, each with a different explanation for the white powder! Can you figure out who the tablet really belongs to?

 

The Bread Baker

The bread baker claims the tablet is his; he kneads bread dough every morning at the mall bakery and uses lots of flour. He claims that he lost his flour-covered tablet during his lunch break.

The Gymnast

The gymnast says the tablet belongs to her. During gymnastics she covers her palms in chalk (calcium carbonate) to absorb sweat and prevent her hands from slipping. She claims that she went to the mall after gymnastics practice and left her chalky tablet there.

The Crepe Maker

The crepe maker makes the most delicious crepes at the mall and uses lots of powdered sugar. She claims the tablet is hers and that she lost it on his way to work that morning. She says it is covered in sugar!

The Hairdresser

The hairdresser’s salon is a very popular stop at the mall. He needs to be sure that his brushes and combs are always clean, so he uses a solution of baking soda (sodium bicarbonate) and water to clean them. He says that he spilled baking soda on his tablet that day and that the tablet must be his.

 

Important safety instructions:

Although these are all household chemicals, any chemical has some risk associated with it. 

• Please wear the safety glasses that we have provided the entire time you are working with these chemicals. 

• Do not eat or drink anything while doing this experiment. 

• Do not touch your face and keep your hands away from your eyes, nose and mouth.

• If you have long hair, tie it back in a pony tail so that it doesn’t get into the chemical experiment.

• The iodine solution will stain your clothes and fingers.  Be extra careful with it.  If you do spill some iodine, wipe it up with paper towels, wash the area with warm water.  The iodine is not toxic when it touches your skin (in fact, iodine solution used to be used as an antiseptic on scrapes and small wounds).  Do not get it in your eyes, mouth or face.

• You can throw the paper waste in the trash, and wash unused chemicals down the sink with water when you are finished.

• Wash your hands with soapy warm water after you are done.

 

Instructions

You have received four packages of identified chemicals and one unknown.  You also have 3 pipettes, 5 paper plates, a small spoon, a small vial of iodine solution and a small bottle of vinegar.  You will also need a cup with some tap water and some paper towels for clean up.

Using a pencil, label each plate with the name of the chemical or unknown.  Then using the spoon, put three small piles of flour on the plate labeled flour, keeping the piles separated.  Wipe the spoon off so that it is clean and doesn’t have any traces of flour on it.

 Make 3 piles of sugar on the plate labeled sugar.  Make 3 piles of baking soda on the plate labeled baking soda.  Make 3 piles of chalk on the plate labeled chalk.  Clean the spoon between each new chemical.

Take one of the pipettes and carefully pipette some water onto one of the piles of each chemical.  Watch what happens and write down what you see in the chart below.

Next using a different pipette, drip some vinegar on the second pile of the chemicals.  Watch what happens and write down what you see in the chart below.

With the third pipette, drop a few drops of iodine solution on the third pile on each plate.  Watch what happens and write it down.

Looking at your chart, can you differentiate the known chemicals based on their reactions with water, vinegar and iodine?

Now make 3 piles of unknown on the plate labeled unknown.  Carefully add water, vinegar and iodine to each pile.  Write it down on the chart and figure out whose computer tablet you have.