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Question 1

what is a pure substance

Answer 1

-a pure element
-a pure compound
-not mixed with any other substance

Question 2

what are properties or a pure substance

Answer 2

-melts at a specific fixed temperature
-has a specific fixed boiling point

Question 3

what are properties of impure substances

Answer 3

-melt and boil over a range of temperatures

Question 4

what is a formulation

Answer 4

-a complex mixture that has been designed as a useful product

-eg fuels,cleaning products,paints,alloys, fertilisers and food

Question 5

what does paper chromatography allow us to do

Answer 5

-allows us to separate substances based on their different solubilities

Question 6

what is the method for carrying out paper chromatography

Answer 6

-take a piece of chromatography paper and draw a pencil line near the bottom
-draw a dot of the colour on the paper(can use several colours)
-place the paper in a solvent
-solvent moves up the paper and dissolves the ink in the dot(s) and carries them up the paper

Question 7

what is the paper and the solvent called within paper chromatography

Answer 7

paper - stationary phase
solvent - mobile phase

Question 8

what does a pure compound and a mixture produce in paper chromatography

Answer 8

-pure compound will produce a single spot in all solvent
-compounds in a mixture may separate into different spots depending on the solvent

Question 9

what does the movement of the colours show us within paper chromatography

Answer 9

-the solubility of a substance
-more soluble substance travels further then a less soluble substance

Question 10

within paper chromatography why do we draw our starting line in pencil?

Answer 10

because if we drew the line in pen, the pen ink would move up the paper with the solvent

Question 11

how can we use paper chromatography ro find an unknown chemical

Answer 11

-place a dot of chemical on a pencil line
-place bottom of chromatography paper in solvent
-measure the distance moved by the unknown chemical
-measure distance moved by the solvent
-find the rf value of the substance
-now look rf value up in a data base

Question 12

how do we figure out the rf value of a substance in paper chromatography

Answer 12

Rf=distance moved by substance/distance moved by solvent

Question 13

what are the problems with looking up the rf value of a substance

Answer 13

-several substances may have the same Rf value
-to fix this we may have to repeat this experiment using different solvents
-if the substance has never been analysed it will not have an rf value

Question 14

what is the test for hydrogen gas

Answer 14

-insert a burning splint into a test tube that you are testing for hydrogen
-if hydrogen is present it will burn rapidly and produce a pop sound

Question 15

how do we test for oxygen gas

Answer 15

-insert a glowing splint into the test tube that you are testing for oxygen
-if the splint relights oxygen is present

Question 16

how do we test for carbon dioxide

Answer 16

-we use limewater(aq calcium hydroxide)
-have one test tube containing carbon dioxide and one containing limewater
-draw the gas into a pipette
-bubble the gas in the limewater
-if limewater turns cloudy the gas was carbon dioxide

Question 17

how do we test for chlorine

Answer 17

-insert damp litmus paper into the mouth of the test tube
-chlorine bleaches the litmus paper and turns it white