LM 1b elements, compounds and mixtures

Question 1

what is an element?

Answer 1

a substance that contains only one type of atom. it cannot be split into anything simpler

Question 2

what is a compound?

Answer 2

a substance made of two or more elements chemically combined

Question 3

what is a mixture?

Answer 3

a mixture of two or more substances that are not chemically combined

Question 4

what are the melting and boiling points of a pure substance?

Answer 4

they will have fixed melting and boiling points if they are pure, mixtures melt and boil over a range of temperatures

Question 5

what does simple distillation do?

Answer 5

separates two liquids with different boiling points

Question 6

what does fractional distillation do?

Answer 6

separates more than two liquids with different boiling points

Question 7

what does filtration do?

Answer 7

separates an insoluble solid from a liquid

Question 8

what does crystallisation do?

Answer 8

separates a soluble solid and a liquid

Question 9

what does paper chromatography do?

Answer 9

separates more than one soluble solid

Question 10

how do you separate a mixture of water and ethanol?

Answer 10

simple distillation

Question 11

what is a molecule?

Answer 11

group of two or more atoms held together by chemical bonds

Question 12

how does chromatography work?

Answer 12

the solvent moves up the marked paper and dissolves the ink.

Question 13

what do we call the paper in chromatography?

Answer 13

stationary phase, doesn’t move

Question 14

what is the solvent called in chromatography?

Answer 14

mobile phase, does move

Question 15

what is an experiment so show the different colours in ink pens?

Answer 15

chromatography

draw a line on the paper chromatography and then put two ink dots, put the paper in a solvent and the colours should move up the paper with the solvent

• if there is only one colour on one of the sides then the colour is pure
• if there were two spots then you can tell the two different colours were a mix

Question 16

how does paper chromatography work?

Answer 16

each chemical in the mixture will be attracted to the stationary phase to a different extent

• chemicals strongly attract will not move very far
• chemicals weakly attracted move further up

Question 17

why do we draw the starting line in pencil in paper chromatography?

Answer 17

because pen ink would move up the paper with the solvent pencil doesn’t

Question 18

how does filtration work?

Answer 18

a mixture is poured through filter paper in a funnel, the insoluble element will get trapped in the filter paper

Question 19

how does crystallisation work?

Answer 19

leave the solution with soluble salt to evaporate, or gently heat

Question 20

how does simple distillation work?

Answer 20

• evaporate liquid by heating

- then cool so the vapour is condensed

Question 21

how does fractional distillation work?

Answer 21

• same thing as simple distillation but with a fractionating column
• liquids in mixture have to have different boiling points
• when vapours hit fractionating column it condenses
• when the boiling point of one of the chemicals is shown on the thermometer there is a relatively pure chemical getting cooled.

Question 22

what is an unsaturated compound?

Answer 22

a compound that hasn’t reached its max amount of bonds

Question 23

what is an unsaturated carbon bond?

Answer 23

a compound that has double carbon bonds

Question 24

how do you test for unsaturated compounds?

Answer 24

bromine water - it turns colourless when added if double carbon bond is present

Question 25

what is an isomer?

Answer 25

compounds with same molecular formula but different structures