Elements, Compounds/ Mixtures, Separation techniques Flashcards
Element
An element is a substance that cannot be broken down into simpler substances by chemical method
Compound
A compound is a pure substance that contains two or more different elements chemically combined, in a fixed ratio
Mixture
A mixture consists of two or more substances that are not chemically combined
Colloid
A colloid is a substance microscopically dispersed evenly throughout another substance.
Atom
An atom is the smallest unit of an element that has the properties of that element
Molecule
A molecule is made of two or more atoms chemically combined together
Soluble
A soluble substance is a substance that can dissolve in a solvent
Filtrate
Substance that is able to pass through the filter paper
Residue
Substance that is unable to pass thru the filter paper
Solute
The substance that is being dissolved
Solvent
The substance that dissolves others
Miscible
Soluble in one another
Immiscible
Insoluble in one another
Properties of elements
- Composition: Made up of only one type of atoms or molecules
- Melting and boiling point: Fixed
- Properties: Has its own set of properties
-cannot be separated
Elements can be broadly classified as?
Metals, non metals and metalloids
Elements=> Metals
- Appearance: Shiny
- Melting and boiling points: High (except for mercury)
- Physical state at r.t.p: Solids at room temperature
- Thermal conductivity: Good
- Malleability: Malleable (can be hammered into different shapes with our breaking)
Elements=> Non-metals
- Appearance: Dull
- Melting and boiling points: Low
- Physical state at r.t.p: Mostly liquids or gases at room temperature
- Thermal conductivity: poor
Malleability: Brittle (break or shatter when hammered)
What is a pure substance?
A pure substance is a single substance that is not contaminated with other substances
Properties of a pure substance
A pure substance has a fixed melting point and boiling point at room temperature and pressure that is not similar to any other substance
How do we check if a substance is pure?
- Check that it has a fixed melting point or boiling point
- Use chromatography paper: There should only be one spot one the chromatogram
Filtration
The bigger solid particles are unable to pass through the small pores of filter paper
Similarities between evaporation to dryness and crystallisation
- both are to obtain the dissolved solid from the solution
Difference between evaporation to dryness and crystallisation
- Evaporation to dryness: Dissolved solid is thermally stable and does not decompose on strong heating
- Crystallisation: Dissolved solid is not thermally stable and decomposes on strong heating
- many crystals give off water to form powders when heated strongly. As such, evaporation to dryness cannot be used to obtain crystals
Process of Evaporation to dryness
- Heat the solution until all the liquid has been evaporated
- The solid left behind is the dissolved solid
Process of crystallisation
- Heat the solution until saturated*
- Dip a clean glass rod into the solution. If crystals form one the rod upon cooling, then the solution is saturated.
- Cool the solution for crystallisation to occur
- Filter the mixture and collect the crystals as residue
- Wash crystals with cold distilled water and dry crystals with filter paper
What is a saturated solution?
A solution is saturated when it contains the maximum amount of solute that can dissolve in a fixed amount of solvent at a specific temperature
Aim of chromatography
- to identify the component present in a sample
- to identify the number of components in a sample
- to determine whether the sample is pure
Process of chromatography
- Draw a line using a pencil, about 2cm from the bottom of chromatography paper to indicate the starting position of the sample. This is called the START LINE
- The chromatography is dipped into the solvent. The mixture dissolves in the solvent and moves up the paper and the mixture gets separated
- The furthest point reached by the solvent is called the SOLVENT FRONT
How does chromatography work?
Different substances have different solubilities in the chosen solvent The more soluble substances dissolve more readily in the solvent and travel further up the chromatography paper compared to less soluble substances
How to calculate RF value?
Distance travelled by solute/ Distance travelled by solvent
Simple distillation
- To obtain a pure solvent from a solution
- This method requires a significant difference in the boiling points between the solute and solvent that make up the solution
How does simple distillation work?
-The water gains heat and boils to form water vapour.
- The water vapour rises and enters the condenser.
- The water vapour will condense into water droplets.
- The water droplets flow out into beaker and is collected (distillate)
Fractional distillation
To separate miscible liquids with different boiling points. The difference in boiling points of the liquids being separate is less significant (compared to simple distillation)
Miscible meaning
Miscible: Able to dissolve in one another and will not form separate layers.
Metalloids
Appearance: Shiny
Physical state at room temperature: solids
Electrical + thermal conductivity: between metals and non metals
Malleability: brittle
Factors affecting rate of dissolving of a solute?
Temperature of a solvent
Rate of stirring
Size of solute particles
Impurities cause the substance to? (Melting and boiling points)
Melting point: decreased
Boiling point: increased
