1.18-1.13 elements, compounds & mixtures

Question 1

describe a molecule

Answer 1

2 or more atoms , held together by chemical bonds

Question 2

describe a compound

Answer 2

2 or more different element held together by chemical bonds

Question 3

describe a mixture

Answer 3

combination of two or more substances that aren’t chemically joined

Question 4

name all the seperation techniques

Answer 4

-filtration
-crystallation
-paper chromotography
-simple distilation
-fractional distilationn

Question 5

describe simple distilation

Answer 5

(seperating a liquid from a solution. (fex. pure water from sea water)

-heat up a mixture so the liquid we want evaporates
-as it rises the pressure will force it to condense
-since the condenser is wrapped in a water jacket, the vapor will cool down, condensing and running down the pipe to be collected in a beaker

Question 6

describe fractional distilation

Answer 6

(seperating mixtures of liquids)

-heat mixture to the temp. of the liquid with the lowest boiling point first causing it to evaporate and condense
-by chance some of the other liquids may evaporate with it but as it goes through the fractionating column (which is much cooler than their boiling points) they will turn back into liquid form and fall back into the flask
-repeat increasing to match the boiling point of all liquids until mixture evaporates

Question 7

describe filtration

Answer 7

(used to seperate insooluble solids from liquid)

-placing filter paper in a filter funnel
-pouring in liquid with insouble solids down it
-leaving the solids on the paper

Question 8

describe crystallation

Answer 8

(seperating soluble solids from liquid usually when prone to decomposition)

-place solution in evaporating dish
-heat it gently using fex. a water bath
-once you start to see crystals forming stop heating and leave it to cool
-finally filter out crystals and dry them out by warming up

Question 9

describe paper chromotography

Answer 9

(used to seperate dyes in an ink)

-take a piece of chromotography paper & draw a line in pencil near the bottom of the sheet (baseline)
-add ink to baseline
-fill a beaker with a shallow amount of solvent (like water or ethanol)
-place filter paper into solvent making sure solvent is below baseline
-wait for solvent to seep up the paper revealing different colors

Question 11

how do you calculate rf value

Answer 11

distance travelled by substance divided by

distance travelled by solvent

Question 12

describe evaporation

Answer 12

(seperating soluble solids from liquid)

-place a solution on an evaporating dish
-slowly heat causing the liquid to start evaporating
-the remaining solution slowly becomes more concentrated
-after a while crystals start
-when all the liquids evaporated only dry crystal solids remain

positives- quick and easy
Negative- some solids decompose when heated