Unit 4: Pure and Impure Substances

Question 1

3 Types of Matter

Answer 1

Element, Compound and Mixture

Question 2

Element

Answer 2

Cannot be separated further. It is the same type of atom.

Question 3

Compound

Answer 3

Can be separated through chemical reactions. A bonded version of 2 or more elements. It is the same type of molecule.

Question 4

Mixture

Answer 4

Cen be separated through chemical and physical reactions. A mixture of 2 or more substances. Not the same type of atom or molecule.

Question 5

Chemical Change

Answer 5

Change in chemical composition aka formula

Question 6

Physical Change

Answer 6

Any change that dosent impact the formula

Question 7

Pure Substances

Answer 7

Elements and Compounds

Substances that are made of only one type of atoms or molecules

Question 8

Impure Substances

Answer 8

Mixtures

Made of more than one type of atom or molecule

Question 9

Name and Define of Mixtures

Answer 9

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).
/
A solute dissolved in a solvent

Question 10

What are Alloys

Answer 10

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

Question 11

Are Alloys stronger than pure metals? If so, why?

Answer 11

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.

Question 12

Examples of Alloys

Answer 12

Bronze, Brass, Carbon, Steel Stainless, Steel, Aluminum Alloys and Gold

Gold = Silver + Gold
Most include Cu

Question 13

Suspension

Answer 13

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

Question 14

Colloid

Answer 14

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

Question 15

Emulsion

Answer 15

A heterogeneous mixture of 2 or more immiscible liquids.

Eventually separate. They don’t settle down.

(eg. mayo, milk, paint, creams.)

Question 16

How are emulsions kept from seperating?

Answer 16

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.

Question 17

What makes an Emulsion, Colloid and Suspension different.

Answer 17

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.

Question 18

Name every technique to separate a Solid from a Solid and What It Does

Answer 18

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.

Question 19

How do you separate an immiscible solid and liquid?

Answer 19

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.

Question 20

How do you separate a miscible solid and liquid?

Answer 20

Evaporation:

1. Place solution in an evaporating dish or crucible and heat it up
2. The solvent (major one) will evaporate, concentrating the solute (minor one)
3. 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.

3. The second there are some crystals, take off heat. Let cool and more crystals will form.
4. Filter than out using filter paper.
5. Let dry in the sun, an oven, etc.

Question 21

Common Mistakes in Crystallisation

Answer 21

Adding too much solvent - it dosent evaporate and crystals dont form

Many tiny crystals = fast cooling rate

Big crystals = slow cooling rate

Question 22

Osmosis

Answer 22

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

Question 23

How do you separate 2 immiscible liquids?

Answer 23

Separating Funnel: Like Sedimentation and Decantation

Uses stopcock to control the on and off instead of pouring

Question 24

How do you separate 2 miscible liquids?

Answer 24

Distillation (Simple)

1. Heat
2. The liquid with the lowest boiling point with evaporate first
3. Then it will condense and turn into distillate

Question 25

What apparatus is used in both kinds of Distillation?

Answer 25

Flask (+cork), Thermometer, Tripod, Bunsen Burner, Condenser, Water Jacket, Beaker, + Fractional Column

Question 26

Explain how the water jacket and condenser in Distillation work

Answer 26

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.

Question 27

Why does Fractional Distillation work?

Answer 27

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.

Question 28

What is Paper Chromatography? + Formula

Answer 28

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

Question 29

Method for Paper Chromatography

Answer 29

1. Take a Porous paper (filter paper) and draw a baseline 2. Then place the ink on the baseline 3. Then add a solvent to a beaker (butane, ethanol, etc.) 4. Place the paper in the beaker, dipping it just enough to not submerge the base line 5. Cover the beaker with a lit to prevent evaporation 6. Wait

Question 30

Reason for solute staying on baseline in Paper Chromatography

Answer 30

It was not soluble with the solvent

Question 31

What causes a single dot in Paper Chromatography?

Answer 31

When a Pure Substance is used

Question 32

How do you know if a dye was more soluble with the solvent in Paper Chromatography?

Answer 32

The dye will be faster aka it would have a longer line on the chromatogram

Question 33

Explain how Crude Oil is seperated

Answer 33

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.

Question 34

What is the main trend in Crude Oil Separation

Answer 34

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.

Question 35

What is 'Cracking' in Crude oil Separation

Answer 35

When a longer hydrocarbon is broken down into a shorter one. It is used to make heavy fuel oil and bitume more useful.

Question 36

Catalytic Cracking

Answer 36

1. Heat up the long hydrocarbon to gas 2. Prepare hot powereded Aluminium oxide (catalyst) 3. Bring long hydrocarbon (g) to 2 It will split into 2

Question 37

Steam Cracking

Answer 37

1. Heat up a long hydrocarbon to gas 2. Mix it with steam and heat to a very high temperature It will split into 2

Question 38

Uses of Halogens (Group 7)

Answer 38

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

Question 39

What is Cloud Seeding?

Answer 39

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