C8 Chemical analysis

Question 1

define pure scientifically

Answer 1

consists of only 1 element or compound

Question 1

define alloy

Answer 1

a mixture of 2 or more elements (usually metals)

Question 2

how many carats gold is 100% gold?

Answer 2

24

Question 3

calculate the percentage of gold if the gild is 9 carat

Answer 3

37.5% gold
9/24 x 100

Question 4

what makes a substance impure?

Answer 4

one different atom of molecule

Question 5

give 3 examples of an alloy

Answer 5

steel, bronze, brass

Question 6

what is steel made out of?

Answer 6

iron + carbon

Question 7

what is steel bronze out of?

Answer 7

copper + iron

Question 8

what is brass made out of?

Answer 8

copper + zinc

Question 9

what is the main property of an impure substance?

Answer 9

the melting point is less then that of a pure substance

Question 10

if a substance is impure, why is the melting point less than that of a pure substance?

Answer 10

because it often melts over a range of temperatures of the substances that its made up

Question 11

how do you know the purity of a substance?

Answer 11

the greater the difference between tis known pure melting point, the lower the purity

Question 12

what is a formulation?

Answer 12

a useful mixture with each substance having a precise purpose

Question 13

how are formulations made?

Answer 13

by mixing the components in carefully measured quantities

Question 14

what are 2 important stages of chromatography?

Answer 14

-the stationary phase
-the mobile phase

Question 15

what are the 2 factors that the travel of a substance in chromatography depend upon?

Answer 15

-how soluble the substance is in the mobile
-the affinity to the stationary phase

Question 16

if there is higher affinity in chromatography how does it affect the travel time?

Answer 16

the slower the substance moves in a set time

Question 17

if there is more solubility in the substance for chromatography how does it affect the travel time?

Answer 17

it moves quicker in a set time

Question 18

in the apparatus setup for chromatography why is there a lid on top?

Answer 18

prevents evaporation of solvent

Question 19

in the apparatus setup for chromatography why is the line a pencil?

Answer 19

the pencil doesn’t dissolve in the solvent

Question 20

in the apparatus setup for chromatography why is water used?

Answer 20

it dissolves colours and is absorbed through the paper

Question 21

describe a method to work out a mixture of colours in the unknown sample is made up of

Answer 21

-use a ruler to draw a pencil line 2cm away from the edge of the paper
-put a small spot of known colourings and the unknown on the line equal distance apart
-label each spot in pencil
-pour water into the beaker but make sure the surface isnt toughing the colourings
-keep the paper vertical and ensure it doesn’t touch the beaker walls
-wait for the water to travel 3/4 up the paper
-remove the paper and wait for it to dry
-calculate the Rf values pf all the coloured spots

Question 22

why do the ink spots in chromatography travel at different distances?

Answer 22

they have different solubilities/ affinities

Question 23

how do you calculate Rf values?

Answer 23

distance moved by the substance / distance moved by the solvent

Question 24

what will a pure compound show after a test of chromatography?

Answer 24

only one spot/ Rf value

Question 25

what is the test for hydrogen?

Answer 25

-quarter fill a test tube w/ hydrochloric acid and add a small piece of magnesium -block the end of the test tube to allow the gas to build up -test the gas with a lighted splint

Question 26

what is the test for oxygen?

Answer 26

-quarter fill a test tube with hydrogen peroxide and add a tiny bit of manganese dioxide powder -block the end of the test tube to allow the gas to build up -test the gas with a glowing splint

Question 27

what is the test for carbon dioxide?

Answer 27

-half fill a test tube with limewater -quarter fill a boiling tube with hydrochloric acid and add some marble chips -put a bung with a delivery tube quickly into the boiling tube and the other end into the limewater

Question 28

what is the test for chlorine?

Answer 28

-switch on the power supply to the electrolysis of sodium chloride --wet a piece of litmus paper and hold it over the positive electrode [if positive then it will blech the damp paper blue]

Question 29

why must the level of solvent in the beaker be below the level of spots in chromatography?

Answer 29

the spots will dissolve in the solvent instead of moving up

Question 30

what can flame tests NOT be used for?

Answer 30

to identify the metals present in a mixture of metal ions

Question 31

what will the stronger colours do in a flame test?

Answer 31

block out the weaker colours

Question 32

what is the line spectrum of a mixture of metal ions?

Answer 32

a combination of the line spectra of each individual metal ion present in the sample

Question 33

what are the pros of chemical analysis?

Answer 33

-often simple to do -cheap

Question 34

what are the cons of chemical analysis?

Answer 34

-uses up the sample -not quantitative

Question 35

what are the pros of instrumental analysis?

Answer 35

-uses small samples (sensitive) -fast -accurate

Question 36

what are the cons of instrumental analysis?

Answer 36

-machines can be expensive

Question 37

what is the flame colour for lithium?

Answer 37

crimson

Question 38

what is the flame colour for sodium?

Answer 38

yellow

Question 39

what is the flame colour for potassium?

Answer 39

lilac

Question 40

what is the flame colour for calcium?

Answer 40

orange-red

Question 41

what is the flame colour for copper?

Answer 41

green

Question 42

what are the Hydroxide precipitates test's method?

Answer 42

Add a few drops of dilute sodium hydroxide solution. Observe and record the colour of any precipitate formed.

Question 43

what precipitate does the positive metal ion aluminium turn (+does it dissolve)?

Answer 43

white - yes

Question 44

what precipitate does the positive metal ion calcium turn (+does it dissolve)?

Answer 44

white - no

Question 45

what precipitate does the positive metal ion magnesium turn (+does it dissolve)?

Answer 45

white - no

Question 46

what precipitate does the positive metal ion copper turn?

Answer 46

blue

Question 47

what precipitate does the positive metal ion iron (II) turn?

Answer 47

green

Question 48

what precipitate does the positive metal ion iron (III) turn?

Answer 48

brown

Question 49

what is the method for the Test for halide ions?

Answer 49

Add a few drops of dilute nitric acid, then a few drops of silver nitrate solution. Observe and record the colour of any precipitate formed.

Question 50

what precipitate colour does chloride form?

Answer 50

white

Question 51

what precipitate colour does bromide form?

Answer 51

cream

Question 52

what precipitate colour does iodide form?

Answer 52

pale yellow

Question 53

what is the test for sulphate ions and what do u see if there is a positive result?

Answer 53

Add a few drops of dilute hydrochloric acid, then a few drops of barium chloride solution. A white precipitate forms if sulphate ions are present.

Question 54

Sulfate ions can be tested for using a dilute acid and which other solution?

Answer 54

barium chloride; Sulfate ions react with barium chloride to form a white precipitate.

Question 55

Some unknown solutions were tested with silver nitrate solution in the presence of dilute nitric acid. The results are shown in the table. Solution 3 did not contain the expected type of ion but another negative ion that reacted with the acid. Name this negative ion.

Answer 55

carbonate ion; Carbonate ions react with the nitric acid to form carbon dioxide gas.

Question 56

In flame emission spectroscopy, a sample is put into a flame and the light that is given out is passed through an instrument. What is the name of the instrument?

Answer 56

spectroscope

Question 57

Complete the sentence. Carbon dioxide gas is produced when an __________ is added to a carbonate.

Answer 57

acid; Acids react with carbonates to form carbon dioxide gas

Question 58

Instrumental methods of identifying ions are particularly useful when the amount of the sample is very __________. What is the missing word in this sentence? large or small

Answer 58

small; Instrumental methods are very sensitive, which means that they can detect very small amounts of a sample.

Question 59

Name a carbonate that is soluble in water.

Answer 59

sodium; The group 1 carbonates are soluble in water, as is ammonium carbonate.