Chemistry test 1
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The most important skill of a forensic scientist is:
the ability to make accurate observations
Who developed the exchange principle -- every contact leaves a trace?
Know the difference between a compound and a element
a compound is a mixture of elements like water (H2O)
What is a chemical property
something that when changed cannot return to the same state.
What is the first step in the scientific method?
Determine the nature of the problem
What is the second step in the scientific method?
Collect and analyze all relevant data
What is the third step in the scientific method
Form a hypothesis (educated guess) as to what happened
What is the fourth step in the scientific method?
Test the hypothesis
What is the fifth step in the scientific method
if Hypothesis holds up to testing you're finished
if not go back to step 2
What are the 5 steps to the scientific method
1- Determine Problem
2- Collect/ analyze relevant data
3- Hypothesis (educated guess)
4- Test Hypothesis
5- If Hypothesis holds test finished if not go to step 2
Know rules for significant figures
1 - zeros located between nonzero numbers are significant (i.e. 101 - 3 sig figures)
2 - Zeros at beginning of number containing decimal are not significant (i.t. 0.015 - 2 sig figures)
3 - Zeros at the end of a number containing a decimal point are significant (i.e. 25.20 - 4 sig figures)
4 - Zeros at the end of a number not containing decimal are ambigous ( i.e. 100 has at least 1 significant figure but can have up to 3)
In accuracy and precision what do they mean?
Accuracy - how close they are to the truth
Precision - how precise are the estamites (how similar they are to each other)
What is physical change?
When something is changed but can come back to original state...
example Ice melting... I can turn it to ice again.
Remember the different metal charts.
What are the 3 states of matter?
Describe the state of matter Solid
Particles are in close proximity and fixed position, hard to compress
Describe the state of matter Liquid
particles are still fairly close,
hard to compress
volume is constant, shape is not
Describe the state of matter Gas
large disctances between particles
always fills volume and shape of container they are in
What is the key difference between a physical change and a chemical change?
Physical changes do not affect identity of the substance
Chemical change changes the identity of substance
How would you determine the density of an irregular shaped object?
1 - Weigh object
2 - submerge in graduated cylinder containing known amount of water
3 - Record how much volume has changed
4 - difference between beginning volume and end volume is volume of object.
5- D=M/V - Divide weight of object by volume to get density
Explain how Mendeleev developed the periodic table
1 - He wrote properties of known elements on card
2 - then arranged them so that there were logical repeating patterns in properties of elements
3 - One of strengths of his arrangement was that he left gaps
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