Unit 4: Pure and Impure Substances Flashcards
3 Types of Matter
Element, Compound and Mixture
Element
Cannot be separated further. It is the same type of atom.
Compound
Can be separated through chemical reactions. A bonded version of 2 or more elements. It is the same type of molecule.
Mixture
Cen be separated through chemical and physical reactions. A mixture of 2 or more substances. Not the same type of atom or molecule.
Chemical Change
Change in chemical composition aka formula
Physical Change
Any change that dosent impact the formula
Pure Substances
Elements and Compounds
Substances that are made of only one type of atoms or molecules
Impure Substances
Mixtures
Made of more than one type of atom or molecule
Name and Define of Mixtures
Heterogeneous: Visibly apparent that there are different substances.
Homogeneous or Solutions: All substances are distributed equally and it all looks the same. (could say diffused).
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A solute dissolved in a solvent
What are Alloys
A homogeneous mixture of 2 or more metals
Their proportion (metal 1’s atoms dont have to be the same size as metal 2’s)
Theyre stronger than pure metals
Part of history - Bronze Age
Are Alloys stronger than pure metals? If so, why?
Because when a force is expelled on a metal, the structure slides.
However because their proportion is not the same, the different sizes of metals can distort the lattice. Thus, the layers dont go over each over as easily.
Examples of Alloys
Bronze, Brass, Carbon, Steel Stainless, Steel, Aluminum Alloys and Gold
Gold = Silver + Gold
Most include Cu
Suspension
A heterogeneous mixture. Can be filtered through filter paper.
A fluid with undissolved solid particles (suspension - when you mix and it all stays together for a minute)
(eg. sand + water)
opaque to light
Colloid
A heterogeneous mixture. Cannot be filtered through filter paper.
A fluid with undissolved solid particles. Unlike suspension, not visible to the naked eye and don’t settle down.
(eg. Aerosols, glues, jelly, and smoke)
transparent or translucent to light
Emulsion
A heterogeneous mixture of 2 or more immiscible liquids.
Eventually separate. They don’t settle down.
(eg. mayo, milk, paint, creams.)
How are emulsions kept from seperating?
Emulsifiers (lecithin)
They have two heads. Hydrophilic and Hydrophohic. Each appeal to one side of the emulsion.
Eg. in water and oil, the hydrophilic will attach to the water and the hydrophohic to the oil. Creating a glue between the two.
What makes an Emulsion, Colloid and Suspension different.
Each mix together two immiscible substances and form heterogrenosu mixtures.
Suspensions: eventually settle down, are visible seeprate and only disper eventuely for one stir
Colloids: dont settle down and are not visibly seprate. Can be between any state if matter.
Emulsions: a collodial system. Nnly between 2 liquids.
Name every technique to separate a Solid from a Solid and What It Does
Handpicking, Magnetic Separation is obvious
Winnowing: Separates lighter and heavier particles using wind (husk and grains)
Sieving: Separates bigger and smaller substances using a sieve
Threshing: Used in farms, to seperate grain from husk. Husk is beaten against something till the grain shakes off.
How do you separate an immiscible solid and liquid?
Sedimentation and Decantation: Let the suspension settle (sedimentation) and then pour out the top layer (decantation), preserving the bottom sediment.
Filtration: Use a filter paper and funnel to allow water to pass through. This leaves behind Solid Residue in the funnel and makes Filtrate.
How do you separate a miscible solid and liquid?
Evaporation:
- Place solution in an evaporating dish or crucible and heat it up
- The solvent (major one) will evaporate, concentrating the solute (minor one)
- This is will make crystals of the solute
(Main Equipment: Crucible, Tripod)
However this does not work for every solid due to Thermal Decomposition.
Crystallisation: is a slower and gentle version. Here we use a hot water bath over a bunsen burner or a very low flame.
- The second there are some crystals, take off heat. Let cool and more crystals will form.
- Filter than out using filter paper.
- Let dry in the sun, an oven, etc.
Common Mistakes in Crystallisation
Adding too much solvent - it dosent evaporate and crystals dont form
Many tiny crystals = fast cooling rate
Big crystals = slow cooling rate
Osmosis
A type of separation that only occurs in water
It uses a semi-permeable membrane to resist the flow of larger particles through.
Used in Dialysis
How do you separate 2 immiscible liquids?
Separating Funnel: Like Sedimentation and Decantation
Uses stopcock to control the on and off instead of pouring
How do you separate 2 miscible liquids?
Distillation (Simple)
- Heat
- The liquid with the lowest boiling point with evaporate first
- Then it will condense and turn into distillate
What apparatus is used in both kinds of Distillation?
Flask (+cork), Thermometer, Tripod, Bunsen Burner, Condenser, Water Jacket, Beaker, + Fractional Column
Explain how the water jacket and condenser in Distillation work
The water jacket and condenser cool down the vapor, which condenses it, because the molecules start to lose energy and come closer. (less temp = less kinetic energy = particles give up)
It creates a top to bottom cooling effect. Which is why the water comes in at the bottom right and goes out at the top right, because the bottom right is the last place the solution can be cooled.
Why does Fractional Distillation work?
The Fractional Column is filled with really cold glass rods.
If A - 2 and B - 4 have really close boiling points, then B will evaporate just a bit after A does. However, after we heat it to 2 and B reaches the Fractional Column, the rods will be much cooler than B’s boiling points. This condenses it and pushes it back down.
What is Paper Chromatography? + Formula
Separating Dyes in a substance using Paper. It produces a Chromatogram.
Rf value = distance travelled by solute/distance travelled by solvent
cannot be >1 and distance travelled by solvent is basically the longest dye’s height
Method for Paper Chromatography
- Take a Porous paper (filter paper) and draw a baseline
- Then place the ink on the baseline
- Then add a solvent to a beaker (butane, ethanol, etc.)
- Place the paper in the beaker, dipping it just enough to not submerge the base line
- Cover the beaker with a lit to prevent evaporation
- Wait
Reason for solute staying on baseline in Paper Chromatography
It was not soluble with the solvent
What causes a single dot in Paper Chromatography?
When a Pure Substance is used
How do you know if a dye was more soluble with the solvent in Paper Chromatography?
The dye will be faster aka it would have a longer line on the chromatogram
Explain how Crude Oil is seperated
Fractional Distillation.
Crude oil is made up of hydrocarbons (long and short)
The crude oil is heated up to vapour form.
Then it is transferred to the Fractional colour, where it separates into 6 substances. Order longest hydrocarbon chain to smallest (bitume, heavy fuel oil, diesel, kerosene, petrol and LPG).
This occurs because the column is very hot at the bottom, and very cold at the top. The heat at the bottom pushes the vapour up. As the vapour progresses, whenever a substance in the vapour moves past its boiling point, it condenses, and is collected.
What is the main trend in Crude Oil Separation
Shorter hydrocarbons are more flammable, and better for fuels.
This includes LPG, Petrol, Kerosene and Diesel.
Longer hydrocarbons are not as useful (heavy fuel oil and bitume), usually they’re used for something else or cracked.
What is ‘Cracking’ in Crude oil Separation
When a longer hydrocarbon is broken down into a shorter one. It is used to make heavy fuel oil and bitume more useful.
Catalytic Cracking
- Heat up the long hydrocarbon to gas
- Prepare hot powereded Aluminium oxide (catalyst)
- Bring long hydrocarbon (g) to 2
It will split into 2
Steam Cracking
- Heat up a long hydrocarbon to gas
- Mix it with steam and heat to a very high temperature
It will split into 2
Uses of Halogens (Group 7)
F - strongest known substance to accept electrons. Used to etch glass, prevent tooth decay, make apatite.
Cl - disinfectants, bleaching agents, paper/wood pulp, salt (for our body).
I - cloud seeing to initiate rain using silver iodide, important for our metabolic rate
Br - Sedatives, other drugs
What is Cloud Seeding?
A weather modification technique that improves a cloud’s ability to produce rain or snow by introducing tiny ice nuclei into certain types of subfreezing clouds
Most cloud seeding operations, use a compound called silver iodide (AgI) to aid in the formation of ice crystals
aka Iodine from Halogens (Group 9)
- Used by United Arab Emirates
