0. Introduction Flashcards
mixture
- two or more substances that are not chemically combined with each other and can be separated by physical means
- the substances in a mixture retain their individual properties
solution
- a special kind of mixture in which one substance dissolves in another
element
- the simplest form of pure substance
- cannot be broken down into anything else by physical or chemical means
compound
- pure substances that are unions of two or more elements
- can be broken into simpler substances by chemical means
What are the two types of mixtures?
Heterogeneous (not the same throughout, particles large enough to be seen) and homogeneous (looks the same throughout, small particles).
Parts of a solution:
- solute (the substance that is dissolved)
- solvent (the substance that dissolves)
Types of solutions (by components):
- gas-gas (air - O&N)
- gas-liquid (soda water - CO2, H2O)
- solid-liquid (ocean water - salts, H2O)
- solid-solid (gold jewelry - Cu, Au (alloys - metals dissolved in metals - stainless steel, brass))
Types of solutions (by amount of solute):
- saturated (contains the maximum quantity of solute that dissolves at that temp.)
- unsaturated (contains less solute than the maximum amount)
(-oversaturated is not a solution but a heterogeneous mixture - too much solute)
electrolytes
solutions of ionic compounds (salts, acids, bases) - completely or nearly completely dissolve into ions
atom
the smallest particle of an element that has the properties of that element (basic building block of matter)
methods of separation
- filtration
- dissolution (solvation)
- crystallization
- evaporation or distillation
- paper chromatography
filtration
the mixture is poured through a paper filter or other porous material (solid-liquid)
dissolution (solvation)
the mixture is added to water or an organic solvent (insoluble substance-soluble substance)
crystallization
the mixture is dissolved in hot water or an organic solvent (e.g. alcohol), the solution cools down, and the crystals formed are isolated by filtration (less soluble substances-more soluble substances)
evaporation/distillation
the mixture is heated up until one or more of its components vaporize(s) (solids/non-volatile liquids-volatile liquids)
- only possible if the two substances don’t have close boiling points
paper chromatography
the mixture is placed on a piece of paper; one side of the paper is submerged in water or a solvent; components move along the paper (less soluble components (move slower/stay in place)-more soluble components (move faster))
- not separating, just proving that there is more than one compound present
- also gel and color chromatography
What are states of matter?
Changes in physical properties of a substance.
- gaseous, liquid, solid, plasma
physical properties
- electrical conductivity
- heat conductivity
- density
- melting point
- boiling point
- index of refraction
- malleability
- ductility
physical change
when a substance changes state but not its chemical composition (form changes but properties stay the same)
index of refraction
extent to which a given material bends light passing through it
What are common signs of a chemical change?
Bubbles, change of mass…
characteristics of chemical change
- reaction with acids/bases
- reaction with oxygen (combustion)
- ability to act as oxidizing/reducing agent
- reaction with other elements
- decomposition into simpler substances
- corrosion
solids
- particles tightly packed
- vibrating around their fixed position
- definite shape and volume (little space between particles)
- infinite free surfaces
liquids
- particles tightly packed but far enough apart to slide over one another
- indefinite shape, definite volume
- one free surface
gases
- particles far apart and move freely
- indefinite shape and volume
- no free surfaces
sublimation
solid to gas
resublimation/deposition
gas to solid
ideal gas particles:
1) random, constant, straight-line motion
2) separated by great distance, volume of particles considered negligible
3) no attractive forces between them
4) collisions might cause transfer of energy but total E of the system remains constant
When does ideal gas differ from a real gas?
1) at high pressure - distance between particles smaller, volume of particles not negligible
2) at low temperatures - particles stagnant, low kinetic E, attraction forces between them present
Why are there horizontal lines on the heating/cooling graph?
The temperature of the substance stays constant because the heat supplied to it is not used to raise the temperature but to break the attraction forces keeping the particles together. This results in a change of state.
Maxwell-Boltzmann distribution curve
Since not all particles are surrounded by the same number of particles, not all of them have the same energy. Some particles have less E than the average and some more. Some have enough E to react (activation energy), and those particles evaporate before the substance’s boiling point is reached.
What is the only way to change the activation energy?
By adding a catalyst (/enzyme).
With higher temperature of the substance, the Maxwell-Boltzmann distribution curve…
…lowers and shifts to the right (bigger portion of it is behind the activation energy barrier).
