principles of chemistry - elements, compounds and mixtures

Question 1

what is an element?

Answer 1

a substance that consists of one type of atom only.

Question 2

what is a compound?

Answer 2

a substance thats made of two or more different elements which are chemically bonded together

Question 3

what is a mixture?

Answer 3

a substance that is made of two or more different elements which are not chemically bonded

Question 4

what is the melting point of pure water?

Answer 4

0°C

Question 5

what is the boiling point of water?

Answer 5

100°C

Question 6

what is filtration?

Answer 6

the separation of an insoluble solid from a liquid. they can be separated using physical methods
1. put filter paper into a funnel
2. pour mixture into it
3. the liquid part of the mixture will run through the paper leaving the solid residue behind.

Question 7

what is crystallisation?

Answer 7

the separation of a soluble solid from a solution
1. pour the solution into an evaporating dish
2. heat the solution
3. some water will evaporate and the solution will get more concentrated
4. once some of the water has evaporated or when crystals start to form, remove the dish from the heat
5. leave the solution to cool
6. the salt will form crystals as it becomes insoluble in the solution
7. filter the crystals out of the solution and leave them in a warm place to dry.

Question 8

how to do paper chromotography?

Answer 8

1. draw a line near the bottom of the filter paper. this is the base line. use a pencil line as pencil marks are insoluble
2. add spots of different inks to the line at regular intervals
3. loosely roll the sheet up and put it in a beaker of solvent e.g. water
4. make sure the level of solvent is below the baseline - you don’t want the inks to dissolve into the solvent
5. place a lid on the container to stop the solvent evaporating
6. the solvent seeps up the paper, carrying the inks with it
7. each different dye in the inks will move up the paper at a different rate and form a spot in a different place.
8. when the solvent has nearly reached the top of the paper, take the paper out of the beaker and leave it to dry
9. the end result is a pattern of spots called a chromatogram.

Question 9

what is simple distillation?

Answer 9

it’s used to separate out solutions
1. first, the solution is heated. the part of the solution that has the lowest boiling point evaporates.
2. the vapour is cooled, turns back into a liquid and is collected.
3. the rest of the solution is left behind in the flask.

Question 10

what is fractional distillation?

Answer 10

it’s used to separate a mixture of liquids
1. put the mixture in a flask and stick a fractionating column on top. then heat it.
2. the different liquids have different boiling points so they will evaporate at different temperatures
3. the liquid with the lowest boiling point evaporates first. when the temperature on the thermometer matches the boiling point, it will reach the top of the column.
4. when the first liquid is collected, raise the temperature until the next one reaches the top

Question 11

what does paper chromatography show?

Answer 11

information about the composition of a mixture

Question 12

how to calculate Rf value

Answer 12

distance travelled by solute/distance travelled by solvent