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Crime Scene Investigation: Who Killed the Owner?

By tabbybaby Nov 12, 2010 768 Words
Susanna Skalikeu
10-6-10
Science
Period 4
Crime Scene Investigation
Background:
The only evidence from the crime was a whitish powder found on the floor. There are three main suspects. The first is Anne Fryer. She uses corn starch (a whitish powder) as the secret ingredient in her stir fry recipe. Bobby Brulee uses baking soda (also a whitish powder) to make his special deserts. Charlie Croissant uses baking powder (also a whitish powder) all the time to fluff up his bread.

Question:
How can you find out who killed the owner… Anne Fryer, Bobby Brulee, or Charlie Croissant?

Observations:
Mr. Brulee’s powder seemed to match the most with the powder form the crime scene. It was the same color and it looked like it had the same texture. Its color was whiter than the rest and its texture was smoother and less bumpy than the other substances.

Hypothesis / Prediction: If you where to test the chemical properties of each substance, then you will find that baking soda matches the substance found at the crime scene because of the physical properties we observed in our observations, baking soda matched the best to the powder found at the crime scene.

Variables:
Manipulated Variable: Type of Liquid.
Responding Variable: Chemical reactions.
Controlled Variable 1: Amount of liquid drops into each sample of powder. Controlled Variable 2:

Materials:

Water - compound
Vinegar – solution (homogeneous mixture)
Potassium Iodine - compound
Corn starch – homogeneous mixture
Baking soda - compound
Baking powder – homogeneous mixture
Micro well
Dropper

Procedure:
1) Gather all materials.
2) In the first vertical row, using a spatula, put the substance found in the crime scene in three vertical holes. 3) In the second vertical row, using a spatula, put baking powder in the three vertical holes. 4) In the third vertical row, using a spatula, put baking soda in the three vertical holes. 5) In the fourth vertical row, using a spatula, put corn starch in the three vertical holes. 6) In the first horizontal row, using the dropper, add one drop of water to each type of substance 7) Record your observations

8) Repeat steps 4-5 with vinegar and Potassium Iodine.
9) Repeat steps 6-8 two more times.
10) Make a data table from your observations.
11) Make conclusion.

Can the solubility property (ability to dissolve in water) be used to distinguish all three materials? No, Solubility cannot be used to distinguish all three materials because it had the same affect on corn starch, baking soda, and on the powder found in the crime scene. It only had a different affect on baking powder. For corn starch, baking soda, and the powder found at the crime scene nothing happened when we added water, but when we added water to baking powder it fizzed, dissolved, and bubbled. Therefore, we would still not have answered our question.

Properties tested:
We tested the chemical properties and the physical properties of each substance. For chemical properties, we tested the substances reactivity. For physical properties, we tested the substances solubility. In our observations, we were also using physical properties.

Analysis / Conclusion:
In conclusion, our prediction was right. We predicted that Bobby Brulee was the killer based off of our observations. The physical properties and the chemical properties of the baking soda matched it to the powder found at the crime scene. For the physical properties, they both had the same color and the same texture. The chemical properties of baking soda and the chemical properties of the powder found in the crime scene also proved our prediction to be right. For chemical properties, when we added water, vinegar, or potassium iodine, both of the powders had the same affect. For water, nothing happened for both of the powders. When we tested the powders with vinegar, both of them started to expand, fizz, and dissolves a lot and really fast. When we tested them with our last liquid, potassium iodine, nothing happened. Therefore, with the chemical and the physical properties of each substance being the same, I accept our prediction.

Next Steps / Future Research: The two main problems that we had were that we didn’t put exactly the same amount of powder in each hole in the microwell. This might have affected out results. The second problem that we had was that it was sometimes difficult to see the reaction when we put the different types of liquids on the powders. For further research, we might test the powders with different liquids such as lemon juice. We can even test them for different chemical properties such as flammability or production of gas.

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