Chem 103 Exam 1

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Forensic definition

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"of the forum" which really takes the science from the lab into the public like public debates and trials

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Forensic science definition

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any science used for the purposes of the law including solving crimes in order to provide impartial scientific evidence for use in the courts of law

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Requirements for forensic science

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knowledge of biology, physics, geology, psychology and chemistry

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Physical evidence

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can be carpet fibers, pet hair, blood gunshot residue and etc

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Evidence is composed of diff types of

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matter, solids, liquids, and gases

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Matter

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anything that takes up space and has mass

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Solids

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definite shape and definite volume, not compressible

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Liquids

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have no definite shape, but do have a definite volume, able to flow

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Gases

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have no definite shape or volume, molecules very far apart, are highly compressible

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Matter can be

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a pure substance or a mixture

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Pure Substance

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the components cannot be separated by any physical means (distillation, etc)

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Mixture

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a blending of two or more "pure substances" with variable composition

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Element

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consists of only one type of atom. It cannot be broken down into any simpler substances by physical or chemical means.

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Compounds

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a structure that consists of two or more atoms that are chemically bound together thus behaves as an independent unit allowed to react chemically and cannot be separated physically

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Mixtures

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a group of two or more elements and/or compounds that are physically intermingled they are physically mixed so they can be separated physical means

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Homogeneous mixtures

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also known as "solution" has the properties throughout the sample such as sugar completely dissolved in water

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Heterogeneous mixture

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consists of two or more regions (phases) that differ in properties

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Matter is a mixture

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it can either be a composition uniform (homogeneous mixture) or not (heterogeneous mixture)

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Matter is a pure substance

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it can either be chemically decomposed (compound) or not (element)

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1869 Russian chemist Dmitri Mendeleev first developed the periodic system which predicts

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chemical formulas and chemical reactions, atomic sizes, and shapes of elements and molecules, physical properties of the elements

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Metals

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majority of elements physical properties: conduct heat/ electricity, solid, metallic luster or shine etc chemical properties: release electrons to form cations

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Nonmetals

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physical properties: often gases, do not conduct, brittle solids, dull appearance chemical properties: react with metals, gain electrons to form anions

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Metalloids

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intermediate properties between metals and non-metals. physical properties: solids, semiconductors. chemical properties: form a variety of ionic electron deficient compounds

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Chain of custody

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chronological documentation showing the seizure, custody, transfer, and analysis of evidence

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Chemical changes

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matter undergoes chemical changes to produce new substances

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Chemical properties

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substance's potential (ability) to react with some other substances in it's environment

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Physical Changes

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changes of a substance between different forms of matter

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Physical properties

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properties measured without changing the chemical composition of the substance

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Extensive

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property that depends on sample size

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Intensive

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properties that are independent of sample size such as color and melting point

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Mass

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a measure of the amount of matter in a sample

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Volume

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a measure of the amount of space the matter takes up

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Density

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ratio of an object mass to it's volume

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Qualitative

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observations of reactions such as changes in color and physical state

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Quantitative

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measurements which involve numbers

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Meter

Kilogram

Second

Kelvin

Mole

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m

kg

s

K

mol

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Kilo

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means 1000 of that unit

1 kilometer = 1000 meters

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Centi

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means 1/100 of that unit

1 meter = 100 centimeters

1 dollar = 100 cents

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milli

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means 1/1000 of that unit

1 liter = 1000 milliliters

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Precision

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refers to reproducibility or how close the measurements are to each other

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Accuracy

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refers to how close a measurement is to the real value

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Densities

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useful physical properties for identifying unknown materials

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sink float method

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involves placing the sample in a liquid of known density. if it floats it is less dense than the liquid. if it sinks, it is more dense

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Density gradient method

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this uses a tall cylinder with a low-density liquid at the top and a high-density liquid at the bottom

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Antoine Lavoisier

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first developed the law of conservation of mass in 1785

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Law of Conservation of Mass

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mass is neither created nor destroyed in a chemical reaction but merely changes form

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Joseph Louis Proust

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first proposed the law of definite proportions

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Law of Definite Proportions

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a chemical compound is always made up of the same relative masses of the elements that compose it

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Law of Multiple Proportions

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whenever two or more elements combine in different rations, different compounds are formed but still in whole number rations

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Mass conservation

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if number of each atom before=after

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Definite composition

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compounds that always have the same atom ratio

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Multiple proportions

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different compounds made of the same elements have small whole number ratios of the elements

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Plum Pudding Model

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with little evidence of how these subatomic particles were setup inside the atom most scientist's thought: Electrons were like raisins (negatively charged) in a positively charge pudding

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Ernest Rutherford (1871-1937)

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Studied Radiation bombarded thing gold foil with a particles and revealed that some of the particles were scattered or deflected from their initial path

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Nuclear Model of the Atom

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Rutherford's publication suggested that atoms have nucleus where all the positive charge and most of the mass inside an atom reside which caused leading chemists to revise the plum pudding atom model

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