Elements, compounds and mixtures Flashcards
What are elements
Elements are pure substances made up of only one type of atom
Name the diatomic elements
Iodine
Bromine
Chlorine
Fluorine
Oxygen
Nitrogen
Hydrogen
What are compounds
Compounds are pure substances made up of two or more different elements that are chemically joined together
What are mixtures
Mixtures are made up of two or more substances which are not chemically joined together
What are mixtures of metals called
Alloys
What are solutions
Solutions are a type of mixture which form when a solute dissolves in a solvent
What is a homogeneous mixture
A homogeneous mixture is a mixture in which the composition is the same throughout
What is a heterogeneous mixture
A heterogeneous mixture is a mixture where the composition is not uniform throughout
What are miscible liquids
Miscible liquids are liquids that form a clear solution when mixed together
What are immiscible liquids
Immiscible liquids are liquids that cannot mix together and form separate layers instead
Give an example of miscible liquids and immiscible liquids
Miscible: Ethanol and Water
Immiscible: Oil and Water
How can you identify pure substances
Pure substances have a sharp melting/boiling point
How do impure substances melt/boil
Impure solids tend to melt over a range of temperatures always lower than the pure substances. Impure liquids boil over a range of temperatures, however if a solid is dissolved in a liquid, it raises the boiling temperature of the liquid
Give differences between mixtures and compounds in terms of composition, properties, melting and boiling temperatures, separation and preparation
Composition: Compounds have a fixed composition where the percentage of each element is always the same, while mixtures don’t have a fixed composition and the percentage of each substance is not always the same
Properties: A compound has its own set of physical and chemical properties, while a mixture keeps the same properties as the substances it is made of
Melting and boiling temperatures: A compound has a fixed melting and boiling temperature, while a mixture melts and boils over a range of temperatures
Separation: A compound needs to be broken down by a chemical reaction, while a mixture can easily be broken down by physical means
Preparation: A chemical reaction needs to take place when a compound is made, while mixtures do not require a chemical reaction
What is filtration used to separate
An insoluble solid from a liquid
Two solids, where one is soluble and the other is insoluble in a solvent
Describe the process of filtration
The mixture is poured into a filter funnel lined with a piece of filter paper. The solid particles are too big to pass through the filter paper, and the solid thus remains on the filter funnel and is collected as the residue. The liquid on the other hand manages to pass through and is collected in a conical flask as the filtrate. The solid is then dried between two pieces of filter paper or in an oven
Where is filtration used in real life
In the making of drinking water, as all solid impurities are removed by filtration
What is distillation used to separate
A solvent from a solution
Two miscible liquids with a large difference in their boiling temperature
Describe the process of simple distillation
The mixture is heated together with anti-bumping granules in a distillation flask. The substance with the lowest boiling temperature turns into vapor, rises up the the flask and enters the condenser. In the cold condenser, the vapor condenses back into a liquid and is collected in a conical flask as the distillate. The substance with the highest boiling point is left behind in the distillation flask
Why is water coming in from the bottom of the condenser instead from the top
When water enters the condenser from the top, both the gravitational force and the force of input are acting downwards, so the water falls quickly and does not reach full volume. When water enters from the bottom, the gravitational force is acting downwards while the input force is acting upwards. Thus, the condenser is filled more slowly and reaches full volume. This leads to cooling being more uniform and no air bubbles forming
Write down 6 precautions for simple distillation
Type of heating: If flammable liquids are to be separated a naked flame should be avoided. Use a water bath or an electric heated instead
The bulb of the thermometer: The bulb of the thermometer should be placed at the mouth of the condenser so that the exact boiling temperature of the liquid can be recorder
Anti-bumping granules: Anti-bumping granules such as glass beads must be used to allow the mixture to boil smoothly by preventing violent boiling
Connections to the condenser: Water in the condenser should be coming in from the bottom and out from the top. This prevents air from being trapped in the condenser, something that would reduce efficiency and increase the risk of the condenser cracking
Collection vessel: The collection vessel should have a narrow opening to reduce the evaporation of volatile distillates
Open apparatus: The apparatus should be open to prevent pressure form building up when it is heated
What are some uses of distillation in real life
Used to make whisky, gin and brandy
Drinking water
What is fractional distillation used to separate
Miscible liquids with a small difference in their boiling temperature (less than 30 degrees)
What is a fractionating column and what does it do
The fractionating is a glass tube packed with glass beads that provide a large surface area on which condensation can take place
Describe the process of fractional distillation
The mixture of water and ethanol is heated in a distillation flask together with some anti-bumping granules. Both liquids evaporate together and a mixture of vapors enters the fractionating column. The large surface area provided by the glass beads inside the column allows separating of vapors to take place. The vapor from the liquid with the lower boiling temperature enters the condenser first, where it condenses back into a liquid and is collected in a conical flask. Once all of the first liquid has distilled, on further heating the higher boiling point liquid will distill over and be collected
Where is fractional distillation used in real life
To obtain ethanol from a mixture of ethanol and water in the fermentation of sugar
Separation of compounds in crude oil
What is crystallization used to separate
A soluble solid from its aqueous solution
Describe the process of crystallization
Heat the solution in an evaporating dish to the point of crystallization until a saturated solution is formed. This can be checked by removing a small quantity of the solution with a glass rod and holding it in the air. If crystals form quickly, then the solution is saturated. The saturated solution is then slowly cooled and crystals start to form. These crystals are filtered from the rest of the solution, washed with cold solvent and dried between two pieces of filter paper
How does the speed of the cooling process of crystallization affect the crystals formed
The slower the cooling process, the bigger and purer the crystals will be
The faster the cooling process, the smaller and less pure the crystals will be
Where is crystallization used in real life
To obtain salt from sea water
To purify sugar
How can two solids be separated with crystallization
When cooling, the most soluble solid will remain in the solution, while the least soluble will crystallize out
What is chromatography used to separate
Dyes from ink
Pigment from plants
Amino acids
Describe the process of chromatography
A spot of the mixture is placed on a pencil line above the bottom edge of a strip of chromatography paper. The chromatography paper is then placed in a boiling tube containing a suitable solvent. The boiling tube is closed with a rubber bung to prevent the evaporation of the solvent that can make the results inaccurate. The solvent begins to rise up the chromatography paper and the different components of the mixture begin to separate. A solute that is very soluble in the solvent travels along the paper faster than a solute that is slightly soluble. The final result is a chromatogram
What does the retardation factor calculate
The Rf factor calculates the movement of a substance during chromatography relative to the movement of the solvent
What is the equation for the Rf factor
distance traveled by solute/ distance traveled by solvent
What precautions do you need to take for a chromatography experiment
A pencil line and not ink line is used to mark the position of the spot of the mixture. This is because ink will also separate and interfere with the results
The beaker should be covered so that the filter paper is surrounded by the vapor of the solvent. This prevents the solvent from escapin which would result in an inefficient separation
The level of the solvent should be below the spot of the mixture. Otherwise, the mixture will dissolve in the solvent and separation won’t occur
