Forensic Chemistry Basics
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1
What is forensic chemistry?
The application of chemical principles and analytical methods to the examination and interpretation of evidence relevant to legal investigations.
2
What is a chemical substance?
Matter with a defined chemical composition and characteristic properties.
3
What is an element?
A pure substance consisting of atoms with the same number of protons.
4
What is a compound?
A substance composed of two or more different elements chemically combined in defined proportions.
5
What is a mixture?
A physical combination of substances that are not chemically bonded together in fixed proportions.
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What is the difference between a homogeneous and a heterogeneous mixture?
A homogeneous mixture has a uniform composition at the observed scale, while a heterogeneous mixture does not.
7
What is an atom's atomic number?
The number of protons in its nucleus.
8
What is an isotope?
An atom of an element having the same number of protons but a different number of neutrons.
9
What is an ion?
An atom or molecule carrying a net electrical charge because of the loss or gain of electrons.
10
What is a cation?
A positively charged ion.
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What is an anion?
A negatively charged ion.
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What is a covalent bond?
A chemical bond formed through the sharing of electron pairs between atoms.
13
What is an ionic bond?
An electrostatic attraction between oppositely charged ions.
14
What is an acid under the Brønsted-Lowry definition?
A substance capable of donating a proton.
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What is a base under the Brønsted-Lowry definition?
A substance capable of accepting a proton.
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What is pH?
A logarithmic measure related to hydrogen ion activity in an aqueous solution.
17
What is the approximate pH of a neutral aqueous solution at 25 degrees Celsius?
7.
18
What does a pH below 7 generally indicate in an aqueous solution at 25 degrees Celsius?
An acidic solution.
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What does a pH above 7 generally indicate in an aqueous solution at 25 degrees Celsius?
A basic or alkaline solution.
20
How does a one-unit decrease in pH affect hydrogen ion activity?
It represents approximately a tenfold increase in hydrogen ion activity.
21
What is a buffer solution?
A solution that resists substantial changes in pH when limited amounts of acid or base are added.
22
What is neutralization?
An acid-base reaction in which an acid and base react, often producing water and a salt.
23
What is solubility?
The maximum amount of a substance that can dissolve in a specified solvent under defined conditions.
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What is a solvent?
The component of a solution that dissolves another substance.
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What is a solute?
A substance dissolved in a solvent to form a solution.
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What is precipitation in chemistry?
The formation of an insoluble solid from a solution through a chemical or physical process.
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What is an oxidation-reduction or redox reaction?
A chemical reaction involving electron transfer or changes in oxidation states.
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What is oxidation?
The loss of electrons or an increase in oxidation state.
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What is reduction?
The gain of electrons or a decrease in oxidation state.
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What is an oxidizing agent?
A substance that accepts electrons and is itself reduced during a redox reaction.
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What is a reducing agent?
A substance that donates electrons and is itself oxidized during a redox reaction.
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What is qualitative chemical analysis?
Analysis intended to identify the presence, identity, or characteristics of substances rather than determine their amounts.
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What is quantitative chemical analysis?
Analysis intended to determine the amount or concentration of a substance.
34
What is molarity?
The number of moles of solute per liter of solution.
35
What is the formula for molarity?
Molarity = moles of solute divided by liters of solution.
36
A solution contains 0.50 mole of solute in 2.0 liters of solution. What is its molarity?
0.25 molar.
37
What does ppm mean in chemical concentration reporting?
Parts per million; its precise mass or volume interpretation depends on the stated measurement basis.
38
What is a dilution factor?
The ratio of final solution volume to the volume of the original solution used, assuming appropriate volumetric preparation.
39
What is the dilution equation for solutions?
C1V1 = C2V2, when the amount of solute remains constant during dilution.
40
What is gravimetric analysis?
Quantitative analysis based on measuring the mass of a substance or a chemically related product.
41
What is titration?
An analytical procedure in which a measured reagent is added to a sample to determine the amount of a target substance.
42
What is the equivalence point in a titration?
The point at which the added reagent and target substance have reacted in the required stoichiometric proportions.
43
What is solvent extraction?
A separation technique that transfers a substance between phases based on differences in solubility or partitioning.
44
What is filtration?
A separation method that passes a mixture through a medium that retains selected particles while allowing fluid to pass.
45
What is centrifugation?
A technique using rotational acceleration to separate components according to differences in sedimentation behavior.
46
What is the purpose of a chemical fume hood?
To capture and exhaust hazardous airborne contaminants generated during appropriate laboratory procedures.
47
Why must forensic chemists consult a safety data sheet or SDS?
It provides information about chemical hazards, safe handling, storage, exposure controls, and emergency measures.
48
What is the purpose of a chemical evidence substrate control?
To assess whether the underlying material or collection medium contributes substances that may affect the analysis.
49
Scenario: A forensic chemist detects a compound in a questioned sample, but the reagent blank also contains that compound. What should be investigated?
Possible contamination from reagents, equipment, or laboratory processing before the sample result is accepted.
50
Scenario: Two chemical samples have the same color and odor but different instrumental spectra. What is the appropriate conclusion?
Their superficial similarities do not establish chemical identity; the spectral differences require evaluation and may distinguish the samples.
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