atoms Flashcards
(28 cards)
what is an atom
smallest part of an element that can exist
what is an element
substance of only one type of atom
elements can be classified into two two groups based on their properties
metals and non metals
elements may combine through chemical reactions to form new products- what are these new substances called
compunds
what are compounds
a substance that contains atoms of two or more different elements, chemically joined together
do compounds have the same properties as their constituent elements
no they have different properties
what is a mixture
consists of two or more elements or compounds not chemically combined together - it does have the same chemical properties.
differences between compounds and mixtures
-compounds have a fixed composition - mixtures don’t
- chemical reactions must occur to separate the elements in a compound - in mixtures they can be separated more easily
- there are chemical bonds between the atoms in compounds but not in mixtures
what are the methods through which mixtures can be separated - do these involve chemical reactions ?
-filtration
-crystallisation
-simple distillation
-fractional distillation
-chromatography
don’t involve chemical reactions
describe and explain simple distillation
-Distillation is used to separate a liquid and soluble solid from a solution (e.g. water from a solution of saltwater) or a pure liquid from a mixture of liquids
- solution is heated and pure water evaporates producing vapour which rises through neck of the round-bottomed flask
- vapour passes through condenser, where it cools and condenses, turning into pure water which is collected in a beaker
-After all the water is evaporated from the solution, only the solid solute will be left behind
-Simple distillation can be used to separate the products of fermentation, such as alcohol and water
describe and explain crystallisation
-This method is used to separate a dissolved solid from a solution
- heat a solution to boiling, remove heat and leave the solvent to evaporate
-The solution is heated, allowing the solvent to evaporate and leaving a saturated solution behind
-If the solution is saturated, crystals will form on the glass rod when it is removed and allowed to cool
-The saturated solution is allowed to cool slowly
Solids will come out of the solution as the solubility decreases
-This will be seen as crystals growing
-They are then washed with distilled water to remove any impurities
describe/explain fractional distillation
- the mixture of liquids is poured into a round-bottomed flask, connected to a water-cooled condenser.
A thermometer is also included to allow measurement of temperature of the gases as they pass through the glassware.
- mixture is heated, and the temp of mixture reaches a point where it equals lowest boiling point in the mixture.
- liquid with that boiling point in the mixture turns into gas and passes through condenser, it is cooled and condenses back into liquid.
- temp is kept constant during this process until no more liquid boils off.
This liquid (referred to as a “fraction”) can then be collected. Once all of the first fraction has been collected,
- temperature is raised until it reaches the next lowest boiling point, and the process is repeated to collect the second fraction.
-This is repeated until all of the liquids in the mixture have been separated by their boiling point.
what is fractional distillation
Fractional distillation is used to separate a mixture of two or more liquids with different boiling points, e.g. the separation of a mixture of different hydrocarbons in crude oil.
describe filtration
-To perform filtration, filter paper is folded into a cone, and inserted into the neck of a filter funnel.
-This is placed into a conical flask, and the mixture is slowly poured into the filter funnel.
-filter paper is designed to allow liquids to pass through, but to prevent solids from passing through,
- so the insoluble solid (called the residue) and liquid (called the filtrate) are separated.
what is filtration
Filtration is used to separate a mixture of an insoluble solid and a liquid (e.g., to separate a mixture of sand and water).
describe evaporation
To perform evaporation, the solution is poured into an evaporating basin and heated. The liquid solvent boils off, leaving the solid solute as residue in the evaporating basin. This technique should only be used when the solute does not break-down at high temperatures, otherwise it can both degrade the solute and release potentially harmful gases.
what is evaporation
Evaporation is used to separate out the solute from a solution, e.g. to separate salt from salt water solution.
describe paper chromatography
-With a ruler and pencil, draw straight line across rectangle of a chromatography paper
2 cm in from the short edge of the rectangle. Note, you must use a pencil for this as a line drawn in ink will dissolve in the solvent.
Pour solvent into a beaker to a depth of 1 cm.
-Using a pipette drop a sample of ink on to the middle of the pencil line and draw a circle around it in pencil.
-Place the chromatography paper into beaker so starting line is just above the solvent. Ensure that ink spot does not fall below solvent surface.
-Place watch glass over top of the beaker and let solvent front move up chromatography paper.
-When it is 1 cm from top of the paper, remove paper from the beaker.
-Using pencil, draw line across solvent front and circle the spots left by the separating ink.
-Using ruler, measure distance between starting line of the experiment and the solvent front.
-Measure the distances that each ink spot has traveled from the starting line.
Calculate the
R
f
R
f
-values for each spot by dividing the distance traveled by the spot by the distance traveled by the solvent front.
what is chromatography
Chromatography can be used to separate mixtures according to the solubility of the components. One common technique is paper chromatography (discussed in more detail here).
what is evaporation
Evaporation is used to separate out the solute from a solution, e.g. to separate salt from salt water solution.
describe evaporation
-To perform evaporation, the solution is poured into an evaporating basin and heated.
-The liquid solvent boils off, leaving the solid solute as residue in the evaporating basin.
This technique should only be used when the solute does not break-down at high temperatures.
-otherwise it can both degrade the solute and release potentially harmful gases.
what is a solution
A mixture of a liquid (solvent) and one or more dissolved solids (solutes).
what is a solvent
A liquid that dissolves certain solutes to make a solution.
what is a solute
A solid that can be dissolved in solvent to make a solution.
