C12

Question 1

what is a pure substance

Answer 1

made up of one just one substance that can be an element or a compound

Question 2

how is the test for water and pure water different

Answer 2

the test for water is that it turns white anhydrous copper sulfate blue but with pure water the test is that the melting point is exactly 0 degrees and the boiling point exactly 100

Question 3

what is a formulation

Answer 3

a mixture that has been designed to give a product the properties to make it most effective at carrying out its function eg with medicinal drugs they often only contain about 5% of the active drug that affects the body to cure illness but they also contain colourants, sweetants, smooth coatings and other compunds to aid their dissolving at the most effective part of the digestive tract

Question 4

paint is a common formualtion. what does it contain?

Answer 4

pigment to provide colour
binder so paint can attach itself to an object and form a protective film when dry
solvent to help pigment and binder spread well by thinning them out

Question 5

what is chromatography used for

Answer 5

to separate and identify mixtures of soluble substances

Question 6

how do chromatography results distinguish between pure and impure substances

Answer 6

pure produces one spot

impure produces 2 or more spots

Question 7

how do you work out Rf values

Answer 7

distance travelled by substance / distance by solvent

Question 8

what are Rf values used for

Answer 8

to identify unknown substances by referring them to databases with known substanes Rf values

Question 9

what is the mobile and stationary phase in paper chromatography

Answer 9

mobile phase - chosen solvent

stationary phase - paper

Question 10

how can you tell whether a substance has a stronger force of attraction to the mobile phase or the stationary phase

Answer 10

a stronger force of attraction to the mobile phase will be carried a greater distance in a given time but a stronger attraction to the stationary phase will not travle as far int the given time

Question 11

what do you have to ensure to make the comparisons between Rf values valid

Answer 11

the solvent and the temperature used are the same as the ones quoted in the database

Question 12

what is the test for hydrogen

Answer 12

hold a lighted splint over an open test tube of hydrogen gas and the lighted splint should ‘pop’

Question 13

what is the test for oxygen

Answer 13

a glowing splint will relight

Question 14

what is the test for carbon dioxide

Answer 14

limewater turns milky

Question 15

what is the test for chlorine

Answer 15

damp blue litmus paper is bleached white

Question 16

what are the flame colours that match with each metal ion

Answer 16

lithium- crimson 
sodium- yellow
potassium- lilac 
calcium- orange red 
copper - green

Question 17

what is the method for carrying out a flame test

Answer 17

1) nichrome wire loop is dipped in concentrated hcl and then heated to clean it. then dip in acid again
2) dip wire into metal compound being tested and hold loop in blue flame
3) flame should change colour and allow you to identify the metal ion

(sometimes if the metal is a mixture then the flame colour could be masked eg intense yellow colour of sodium ions can mask the others)

Question 18

what can you tell if you react something with sodium hydroxide and a white precipitate forms

Answer 18

it is either aluminium, calcium or magnesium

Question 19

what happens to precipitate formed by aluminium ions when excess sodium hydroxide is added

Answer 19

it dissolves however calcium and magnesium precipitates wont dissolve

Question 20

how can you differentiate between calcium and magnesium precipitates

Answer 20

flame test
mg- no colour
ca- orange red flame

Question 21

what happens if you add sodium hydroxide solution to a substance containing a) copper (ii) ions

b) iron (ii) ions
c) iron (iii) ions

Answer 21

a) blue precipitate appears
b) green precipitate
c) brown precipitate

Question 22

what is the test for a carbonate

Answer 22

if you add dilute acid to a carbonate it will fizz and produce co2 gas

Question 23

how can you differentiate group 1 carbonates from other carbonates

Answer 23

group 1 carbonates dissolve in water

Question 24

what is the test for halides ( chlorides, bromides and iodides)

Answer 24

add dilute nitric acid and then silver nitrate solution and if a precipitate forms then it is a halide

Question 25

what is the test for sulfates

Answer 25

add dilute hcl followed by barium chloride solution. the white precipitate tells you a sulfate is present

Question 26

what are the advantages and disadvantages of instrumental methods

Answer 26

adv:
highly accurate and sensitive
quick
enable small samples to be analysed

disadv:
expensive
takes training to use
results ususally have to be compared with data from known substances

Question 27

what is flame emission spectroscopy

Answer 27

to analyse samples for metal ions by heating it in a flame. this extra energy causes electrons to jump into higher energy levels. then when they fall back to the lower energy levels the energy is released as light

Question 28

how does the spectrometer analyse the light given out

Answer 28

the wavelengths are passed through a spectroscope which reads the line spectrum of the light that can then be compared to a database

Question 29

what is flame emission spectroscopy used for in industry

Answer 29

to test water for levels of metel eg mercury which is toxic