chapter 1 chem Flashcards
what is an element
when all the atoms are the same
what is a compound
two or more different elements chemically combined in a fixed proportion
what is a mixture
elements or compounds which are not chemically combined
what is a molecule
any elements chemically joined
how can you tell if something is a compound
as they have completely different properties form the elements they are made form
how do we separate mixtures
by using a physical separation technique e.g filtration
how doe we seperate compounds
by using chemical reactions
what are the physical separation techniques
filtration
chromatography
simple distillation
fractional distillation
crystallisation
what is filtration used for
to sperate an insoluble solid from a liquid
what does insoluble mean
a solid will not dissolve in a liquid
how does filtration work
1) pour the mixture in the filtration paper which is inside the funnel
2) the liquid will then pass through the tiny pores of the filter paper
3) the solid will stay in the filter paper as it cant pass through it
what is crystallisation used for
to sperate a soluble solid form a liquid
how does crystallisation work
1) heat a solution in an evaporating dish in a water bath
2) stop the heating as soon as the substance is at the point of crystallisation
3) leave the solution to evaporate and crystals should appear on the edge of the dish
when do we use simple distillation
to separate a liquid from a solid if we want to keep the liquid
how does simple distillation
1) we heat a solution placed in the round bottom flask
2) as we heat the liquid it starts to evaporate turning it into a vapour
3) the vapour passes into the condenser and condenses it a liquid
3) we then collect the liquid in a boiling tube
why does tap water continuously run through the condenser in simple distillation
to keep the internal glass tube (condesor) cold
what is fractional distillation used for
to separate a mixture of different liquids with different boiling points
how does fractional distillation used
1) gently heat the mixture causing both of the liquid to evaporate, the one with the lowest boiling point will evaporate more easily
2) when the vapours reach the fractionating column they condense and drip back into the flask where the liquids evaporate again
3) this repeated amount of condensation and evaporation increase the amount of the lower boiling point chemical in the fractionating column
4) as the warm vapours reaches up the column they reach the thermometer causing the temperature to rise
6) these vapours pass down the condenser and turn into a liquid, this liquid is a mixture of both chemicals however it has a higher conc of the chemical with the lower bp
7) once the temperature of the thermometer reaches the bp of the chemical with the lowest bp, that chemical then mainly passes through the condenser so this condenses and we can collect it in a new beaker
8) after a while the temp of the thermometer begins to rise again so we then start collecting both chemicals but once the tep is constant again we only recieve the other chemical
what is paper chromatography used for
to sperate substances based on their different solubilities
how does paper chromatography work
1) draw a pencil line near the bottom of the paper
2) draw a dot of the first substance on the pencil line and continue to do this with different substances until their is no room on the paper
3) place the bottom of the paper into a solvent
4) the solvent then makes its way up the paper and dissolves the substance carrying the dots up the paper as well
why is the paper the stationary phase in chromatography
as it does not move
why is the solvent the mobile phase in chromatography
as it moves
why does paper chromatography work
as each chemical in the mixture will be attracted to the stationary phase to a different extent, this means that chemicals that are strongly attracted to the stationary phase will not move very far and chemicals that are weakly attracted will move further up the paper
what did the ancient greeks believe about atoms
- that everything is made from atoms
- atoms are tiny spheres that cannot be divided
what was the plum pudding model
it was the model of the atom that showed that
- atoms we a ball of positive charge with negative electrons embedded in it
what happened in the alpha scattering experiment
1) the scientist took a piece of gold foil, as it could be hammered out into very thin foil
2) they then fired alpha particles at the gold
3) most of the alpha particles past straight through the gold foil without changing direction
4) sometimes the alpha particle was deflected
5) sometimes the alpha particles bounced straight back off the gold foil
What did scientist find out from the results of the alpha particle experiment
1) as most of the alpha particle went straight through the foils showed that atoms were mainly made out of empty space
2) as some of the alpha particles we deflected it meant that the centre f the atom must have a positive charge, as the alpha particles that came close to it were repelled and changed direction
3) as some particles bounced straight back it meant that the centre of an atom contained a great deal of mass
what is shown in the nuclear model after the alpha particle experiment
in the centre there is a positive charged nucleus
lots of empty space
negative electrons all around the edge
