chemical analysis

Question 1

what is a pure substance

Answer 1

a substance which is made up of one substance which is either an element or a compound

Question 2

how do you test if water is present

Answer 2

the substance turns white anhydrous copper sulphate blue

Question 3

how do you test for pure water

Answer 3

the melting point of pure water is exactly 0 and boiling point is exactly 100

Question 4

what will happen to the melting point of a mixture

Answer 4

it will not be fixed and will vary. it will have changes of state over a variety of temperatures

Question 5

what do impurities do to boiling and melting points of substances

Answer 5

lower the melting point and raise the boiling point

Question 6

what is a formulation

Answer 6

a mixture which has been designed to produce a useful product

Question 7

2 examples of formulations

Answer 7

fuels, alloys

Question 8

what are the two phases involved in chromatography

Answer 8

the mobile phase and the stationary phase

Question 9

what can chromatography be used for

Answer 9

to separate and identify mixtures of amino acids

Question 10

what will differ between each component in a mixture

Answer 10

each component will have a different attraction to the mobile and stationary phase

Question 11

what will happen to a component which has a stronger force of attraction to the mobile phase than the stationary phase

Answer 11

the component will travel a greater distance

Question 12

what will happen to a component with a stronger force of attraction to the stationary phase than the mobile phase

Answer 12

it will not travel as far

Question 13

what does multiple dots on a chromatography sheet suggest about the component

Answer 13

it is a mixture

Question 14

how do you calculate retention factor

Answer 14

distance moved by substance/distance moved by solvent

Question 15

what is the test for hydrogen

Answer 15

a lighted splint pops

Question 16

test for oxygen

Answer 16

a glowing splint relights

Question 17

test for carbon dioxide

Answer 17

limewater turns milky / cloudy white

Question 18

test for chlorine

Answer 18

damp blue litmus paper turns white

Question 19

what is used to identify positive ions

Answer 19

sodium hydroxide

Question 20

what precipitates form when aluminium, magnesium and calcium ions are mixed with sodium hydroxide

Answer 20

white precipitates

Question 21

what is the ionic equation for the reaction with aluminium ions

Answer 21

Al3+ + 3OH- —> Al(OH)3

Question 22

Copper + sodium hydroxide = ?

Answer 22

blue precipirate

Question 23

iron (II) + sodium hydroxide = ?

Answer 23

green precipitate

Question 24

iron (III) + sodium hydroxide = ?

Answer 24

brown precipirate

Question 25

Lithium in a flame = ?

Answer 25

crimson

Question 26

sodium in a flame = ?

Answer 26

yellow

Question 27

potassium in a flame = ?

Answer 27

lilac

Question 28

calcium in a flame = ?

Answer 28

orange-red

Question 29

copper in a flame = ?

Answer 29

green

Question 30

what should be used to hold the acid while performing a flame test and how do you clean it

Answer 30

a nichrome wire loop should be used. it should be dipped in hydrochloric acid and then heated and then dipped in the hydrochloric acid again to clean it before dipping it in the metal compound

Question 31

why might a flame be two different colours

Answer 31

because it is a mixture

Question 32

how do you identify carbonates

Answer 32

if you add the suspected carbonate to dilute hydrochloric acid it fizzes and produces carbon dioxide. If the gas produced forms a white/cloudy precipitate in lime water it is a carbonate

Question 33

what would you use to test for halides

Answer 33

dilute nitric acid and then silver nitrate. The dilute nitric acid would dissolve the compound and remove any carbonate ions. The silver nitrate would cause the colour change

Question 34

iodide ions + silver nitrate = ?

Answer 34

yellow precipitate

Question 35

bromide ions + silver nitrate = ?

Answer 35

cream precipitate

Question 36

chloride ions + silver nitrate = ?

Answer 36

white precipitate

Question 37

what do you use to test for sulphates

Answer 37

dilute hydrochloric acid and then barium chloride solution. the barium solution will turn the solution a white precipitate.

Question 38

what is flame emission spectroscopy

Answer 38

- a sample is heated in a flame - the energy excites electrons in the metal ions causing the to jump from electron shells - when the electrons return to their energy levels when they cool, light energy is emitted - the spectrometer analyses the wavelengths produced which can then be identified to find out what metal ion is present - the spectrometer can also measure the intensity of the wavelength which indicates the concentration