Science - Chemistry - Chemical Analysis - C8

Question 1

what is purity ?

Answer 1

a substance in its natural state which only contains one type of element

Question 2

what does a chemically pure substance have ?

Answer 2

a specific melting point

Question 3

how can you test a a substances purity ?

Answer 3

by measuring its melting/boiling point

Question 4

what will impurites in substances do ?

Answer 4

lower your melting point and increase the melting range of your substance
increase boiling point over a range of temperatures

Question 5

what are formulations ?

Answer 5

useful mixtures with a precise purpose made by a formula

Question 6

give an example of a formula ?

Answer 6

paint

Question 7

why are formulations important ?

Answer 7

• altering formulations of a pill makes sure that a drug is delivered to the right part of the body

Question 8

what is chromatography ?

Answer 8

separating substances in a mixture

Question 9

what are the 2 phases of chromatography ?

Answer 9

mobile phase
stationary phase

Question 10

what is the mobile phase ?

Answer 10

where molecules can move in a liquid or gas

Question 11

what is a stationary phase ?

Answer 11

molecules can’t move , can be a thick liquid or solid

Question 12

what happens in chromatography ?

Answer 12

• substances in the sample moves between the 2 stages
• an equilibrium is formed between the 2 stages
• the mobile phase moves through the stationary phase and anything dissolved in the mobile phase moves with it

Question 13

what does how quickly a chemical moves depend on ?

Answer 13

it distribution

Question 14

what is a chemicals distribution ?

Answer 14

whether the chemical spends more time in the mobile or stationary phase

Question 15

what phase to most components in a substance normally separates in ?

Answer 15

the stationary phase as long as all components spend different amounts of time in the mobile phase

Question 16

why, in paper chromatography may the number of spots formed change in different solvents ?

Answer 16

the distribution of chemicals is the same in some solvents but different in others

Question 17

how many spots will a pure substance always form ?

Answer 17

1 spot in any solvent

Question 18

what is the stationary phase in paper chromatography ?

Answer 18

the filter paper

Question 19

what is the the mobile phase in paper chromatography ?

Answer 19

the solvent

Question 20

what does the amount of time spent in each phase in paper chromatography depend on ?

Answer 20

• how soluble they are in the solvent
• how attracted they are in the paper

Question 21

what stage do molecules with a higher solubility spend longer in ? (paper chromatography)

Answer 21

the mobile phase

Question 22

what do molecules with higher solubility do in paper chromatography ?

Answer 22

travel up the paper higher and are less attracted to the paper

Question 23

what is a chromatogram ?

Answer 23

the result of a chromatography experiment

Question 24

what is the RF value ?

Answer 24

the ratio between the distance travelled by the substance and the distance travelled by the solvent

Question 25

how do you calculate RF value ?

Answer 25

distance travelled by substance / distance travelled by solvent

Question 26

what is the test for oxygen ?

Answer 26

it will relight a glowing splint

Question 27

what is the test for chlorine ?

Answer 27

it bleaches damp litmus paper

Question 28

what is the test for hydrogen ?

Answer 28

hold a lit splint at the open end of a test tube you will hear a squeaky pop when you release

Question 29

what is the test for carbon dioxide ?

Answer 29

solution of calcium hydroxide (limewater) in a test tube and blow into the test tube, if carbon dioxide is present the solution will turn cloudy

Question 30

what charge ion do flame tests test for ?

Answer 30

positive ions

Question 31

why are flame tests used to test for positive ions ?

Answer 31

metal compounds burn with colour

Question 32

how do flame tests work ?

Answer 32

put sample in flame and observe the colour change

Question 33

what colour does lithium burn ?

Answer 33

crimson

Question 34

what colour does sodium burn ?

Answer 34

yellow

Question 35

what colour does potassium burn ?

Answer 35

lilac

Question 36

what colour does calcium burn ?

Answer 36

orange

Question 37

what colour does copper burn ?

Answer 37

green

Question 38

describe step by step how to carry out a flame test ?

Answer 38

1. clean nichrome wire loop by dipping it in HCL and holding over blue flame until the flame doesn't burn another colour 2. dip wire in sample and record the colour of the flame

Question 39

what is a precipiate reaction ?

Answer 39

add drops of sodium hydroxide into the sample and if you get an insoluble coloured metal hydroxide you know what metal your testing

Question 40

what colour does copper turn in precipitate reactions ?

Answer 40

blue

Question 41

what is the equation for copper in a precipitate reaction ?

Answer 41

Cu2+ + 2OH- - Cu(OH)2

Question 42

what colour does iron turn in precipitate reactions ? ( WITH 2 CHARGE )

Answer 42

green

Question 43

what is the reaction for iron 2 charge in a precipitate reaction ?

Answer 43

Fe2+ + 2OH- - Fe(OH)2

Question 44

what is the equation for iron 3 chargw in a precipiate reaction ?

Answer 44

Fe3+ + 3OH- - Fe(OH)3

Question 45

what colour does iron turn in a precipitate reaction - 3 charge ?

Answer 45

brown

Question 46

what colour does magnesium turn in a precipitate reaction ?

Answer 46

white

Question 47

what colour does aluminium turn in a precipitate reaction ?

Answer 47

white then colourless

Question 48

what is the equation for aluminium in a precipitate reaction ?

Answer 48

Al3+ + 3OH- - Al(OH)3

Question 49

what is the equation for magnesium in a precipitate reaction ?

Answer 49

Mg2+ + 2OH- - Mg (OH)

Question 50

what are negative ion tests we need to know ?

Answer 50

carbonate ions halide ions sulfate ion

Question 51

what is the test for carbonate ions?

Answer 51

when a carbonate ion reacts with dilute acid you get salt, water and CO2 so use the test for carbon dioxide to test for these ions

Question 52

what is the test for halide ions ?

Answer 52

add dilute nitric acid followed by silver nitrate solution

Question 53

what colour does chloride turn when testing for halide ions ?

Answer 53

white

Question 54

what is the equation for chloride when testing for halide ions ?

Answer 54

Ag+ + Cl- - AgCl

Question 55

what colour does bromide turn when testing for halide ions ?

Answer 55

cream

Question 56

what is the equation for bromide when testing for halide ions ?

Answer 56

Ag+ + Br- - AgBr

Question 57

what colour does iodide turn when testing for halide ions ?

Answer 57

yellow

Question 58

what is the equation for iodide when testing for halide ions ?

Answer 58

Ag+ + I- - AgI

Question 59

how do you test for sulfate ions ?

Answer 59

add dilute HCL then barium chloride (BaCl2)

Question 60

how do you know the compound was a sulfate when testing for sulfate ions ?

Answer 60

white precipiate of barium sulfate is formed

Question 61

what is the equation for a positive sulfate ions ?

Answer 61

Ba2+ + SO2- - BaSO

Question 62

why is HCL used when testing for sulfate ions ?

Answer 62

to remove any carbonate ions which might be present so it doesn't confuse results

Question 63

what happens during flame emission spectroscopy ?

Answer 63

1. a sample is placed in a flame as the ions heat up, and electrons get excited 2. when electrons drop back to get to original energy levels they transfer the energy as light 3. light passes through the spectroscope which detects different wavelengths of light to produce a line spectrum 4. combination of wavelengths emitted by an ion depends on its charge and electron arrangement 5. as no ions have the same charge and electron arrangement each ion produces a different pattern of wavelengths 6. intensity of a spectrum indicates the concentration of the ion

Question 64

what are the advantages of using flame emission spectroscopy ?

Answer 64

- sensitive, picks up tiniest amounts of things - fast - accurate

Question 65

what does flame emission spectroscopy identify ?

Answer 65

only a single metal not a mixture of ions, but identities a mixture of ions in a solution can be found