Date post: | 28-Dec-2015 |
Category: |
Documents |
Upload: | alaina-hamilton |
View: | 214 times |
Download: | 0 times |
CH. 2.1MATTER AND CHANGE
CH. 2.1DESCRIBING MATTER
• Observation: using your senses to describe.• White, waxy substance
• Inference: making a conclusion• made of wax.
DESCRIBING MATTER
• Qualitative: describing matter using the senses.
• White, smooth, circular, smells like flowers, warm
• Quantitative: numerically descriptive
• 8.5 cm high, weighs 85 grams.
DESCRIBING MATTER
• Extensive Property: depends on the amount of the sample. (can vary from sample to sample even if same substance)
• Weight, volume, height, shape
• Intensive Property: depends on type (composition) of substance. (doesn’t change as long as samples are made of same substance)
• Color, melting point, reaction with other things
GIVE EXAMPLES OF EXTENSIVE AND INTENSIVE PROPERTIES OF THESE 2 SAMPLES OF SILICON
IDENTIFYING SUBSTANCES
• Physical Property: quality/condition of
substance that can be observed or measured
w/o changing substance.
• Color, weight, size, volume
• ,
IDENTIFYING SUBSTANCES
• Physical Change: changing the state but not the
composition.
• Melting, boiling, vaporizing, freezing, crushing, dissolving
IDENTIFYING SUBSTANCES
• Chemical Property: how a substance react with another substance.
• Iron reacts with oxygen.
• Chemical Change: the reaction that takes place
when two substances react (Chemical
Reaction). Composition changes. (observe
bubbling, color change, precipitate)
• Iron reacts with oxygen to make rust.
COMMON STATES OF MATTER
• Solid: definite shape and
volume
• Liquid: indefinite shape,
flows, definite volume.
• Gas (Vapor): indefinite
shape and volume, flows.
Ch. 2.2-2.4
Mixtures, Elements, Compounds
Symbols
• Chemists use chemical symbols to represent elements• Chemical Symbol: 1st 1-2 letters of the name of the element
– 1st letter is always Capitalized– 2nd letter is always lower case– Examples: Co = Cobalt; O = Oxygen;
Be = Berylium
Exception: Some use the letters from the Latin name– Examples: Fe = Iron (Ferrum)
K = Potassium (Kalium)
Cu = Copper (Cuprium)
Formulas
• Chemists use chemical formulas to represent compounds– Compounds: 2 or more elements– Examples: NaCl = Sodium Chloride
H2O = Water
Breaking up
• Compounds can be broken down into simpler substances by chemical means, but elements cannot
• Chemical changes can be used to break down the substances– Heating sugar can be heated until it breaks
down into solid carbon and water vapor
Properties
• Properties of compounds differ greatly from the properties of the individual elements that make them up– Solid sodium is extremely reactive– Chlorine is a gas– Combined they make up sodium chloride, aka
table salt
Na + Cl2 → NaClSodium + Chlorine → Table salt
H2 + O2 → H2O
Classifying mixtures
• A mixture is a physical blend of two or more components
• Based on the distribution of the components, mixtures can be classified as heterogeneous or homogeneous mixtures
• Heterogeneous mixture: a mixture in which the composition is not uniform throughout– Ex: oil and vinegar, sand in water
• Homogeneous mixture: a mixture in which the composition is uniform throughout– Also known as a solution
Homogeneous mixtures
• Many solutions are liquid, but can also be gas (air) or solids (stainless steel)
• The term “phase” can be used to describe any part of a sample with uniform composition and properties– Homogeneous mixtures have 1 phase
Heterogeneous V. Homogeneous
Distinguishing Substance and Mixtures
Matter
Substance:Definite Composition
(Homogeneous)
Mixture of Substance:
Variable Composition
ElementEx: Sodium Na
CompoundEx: Sodium Chloride
Homogeneous
Mixture:Uniform; also called
a SolutionEx: Salt in Water
Heterogeneous Mixture:
Non-uniform;Distinct phases
Ex: Milk
Separating mixtures
• Different physical properties can be used to separate mixtures– Different BPs or MPs can be used
• Filtration: separates a solid from a liquid– Coffee filters separate grounds from water
• Distillation: a liquid is boiled to produce a vapor then condensed into a liquid
Paper chromatographySeparating a mixture
Chemical reactions
• Chemical changes are signs of chemical reactions happening– Iron reacting with oxygen to form rust
– Fe + O2 → Fe2O3
• During a chemical reaction, the composition of matter always changes
• Fe + O2 → Fe2O3
Reactants Products
• A substance present at the start of a chemical reaction is called a “reactant”
• A substance produced in the reaction is the “product”
• Reactants react to produce products
Recognizing chemical reactions
• Signs a reaction may have occurred:– Production of gas or bubbles– Change in color– Change in temperature– Precipitate forms
• A solid that forms and settles out of a liquid mixture
Law of Conservation of Mass
• During any chemical reaction or physical change, the mass of the products is always equal to the mass of the reactants
• Bottom line: you cannot create or destroy matter. Matter is conserved.