chemical analysis

Question 1

pure substances and formulations
-a pure substance can be a single element
-a pure substance can also be a single compound
-a pure substance is not mixed with any other substance
what is true about a pure susbatnce’s melting and boiling point (Pick 2)
A) a pure substance melts over a range of temperatures
B) a pure substance boils at a specific fixed temperature
C) a pure substance melts at a specific fixed temperature
D) a pure substance boils over a range of temperatures

Answer 1

B) a pure substance has a specific fixed boiling point

C) a pure substance melts at a specific fixed fixed temperature

Question 2

impure substances melt and boil over a range of temperatures

if a sample of water boils over a range of temperatures is it pure or impure?

Answer 2

is the sample boils over a range of temperatures than it is an impure substance because impure substances boil over a range of temperatures

Question 3

what are formulations

Answer 3

formulations are a complex mixture that has been designed as a useful product
in a formulation quantity of each component is carefully measured so that the product has the properties we need.

Question 4

examples of formulations

Answer 4

• fuels
• cleaning products
• alloys
• fertilisers
• medicine
• paint

Question 5

All separation techniques including paper chromatogrpahy are physical processes
why

Answer 5

because they do not involve chemical reactions, no new substances are made

Question 6

what is paper chromatography

Answer 6

paper chromatography allows us to separate substances based on their different solubilities

Question 7

how do we carry out paper chromatography

Answer 7

we take a piece of chromatography paper and draw a pencil line at the bottom. we put a dot of our first colour on the pencil line
now we put a dot of our second colour
we must do this for several colours as long as there is enough space on the paper.
now place bottom of paper into a solvent
solvent makes its way up the paper and dissolves the ink. these are carried up the paper as well

Question 8

how do we carry out paper chromatography

Answer 8

we take a piece of chromatography paper and draw a pencil line at the bottom. we put a dot of our first colour on the pencil line
now we put a dot of our second colour
we must do this for several colours as long as there is enough space on the paper.
now place bottom of paper into a solvent
solvent makes its way up the paper and dissolves the ink. these are carried up the paper as well

Question 9

what is the definition of a solvent

Answer 9

liquid that will dissolve substances

Question 10

what is the stationary phase and what is the mobile phase

Answer 10

stationary phase- paper ( does not move)

mobile phase- solvent ( moves up the paper)

Question 11

pure substances will produce a single spot because…

Answer 11

pure substances will produce a single spot because they are not mixed with any other substance.

Question 12

in context: if one of the colours has separated into two different spots what does it mean

Answer 12

it is a mixture of two different substances

Question 13

why does paper chromatography work

Answer 13

because each chemical in the mixture is attracted to the stationary phase to a different extent.

Question 14

chemicals that are strongly attracted to the stationary phase will:
A) move further up the paper
B) not move very far

Answer 14

A) chemicals that are strongly attracted to the stationary phase will not move very far

Question 15

chemicals that are weakly attracted to the stationary phase will move:
A) further up the paper
B) not very far

Answer 15

A) chemicals that are weakly attracted to the stationary phase will move further up the paper

Question 16

remember a pure substance will produce a single spot in ALL solvents

Answer 16

• a pure substance will produce a single spot in ALL solvents

Question 17

chemicals in a mixture may separate into different spots depending on the solvent

Answer 17

chemicals in a mixture may separate into different spots depending on the solvent

Question 18

why do we draw the starting line in pencil

Answer 18

pen ink would move up the paper with the solvent

Question 19

testing for gases

describe how to test for hydrogen gas?

Answer 19

• remove the bung of the test tube and bring a burning splint towards mouth of test tube. hydrogen will burn rapidly and produce a squeaky pop sound

Question 20

describe how to test for oxygen gas?

Answer 20

• bring a glowing splint towards the mouth of the test tube

- if the splint relights then oxygen gas is present

Question 21

describe how to test for carbon dioxide gas

Answer 21

• draw up some gas into a plastic pipette.
• bubble gas through test tube
• if limewater turns cloudy then carbon dioxide is present

Question 22

describe how to test for chlorine gas

Answer 22

-bring damp litmus paper into mouth of test tube

chlorine would bleach the damp litmus paper white

Question 23

what is limewater? ( could ask in exam)

Answer 23

limewater is an aqueous solution of calcium hydroxide

Question 24

Flame tests- how does it work explain steps briefly

Answer 24

1) First we place a small amount of our chemical onto a wire mounted in a handle
2) place end of this into a roaring (blue) bunsen burner flame
3) the colour of the flame can help us identify the metal ion

Question 25

``` list all the colours of the flames of these metal ions: lithium sodium potassium calcium copper ```

Answer 25

- lithium= produces a crimson flame - sodium=produces a yellow flame - potassium= produces a lilac flame - calcium= produces an orange red flame - copper=produces a green flame

Question 26

identify the problems of using flame tests to identify metal ions:

Answer 26

- sometimes, the colour can be difficult to distinguish this is especially true if there is a low concentration of the metal compound - sample may contain a mixture of different metal ions which could mask the colour of the flame

Question 27

flame emission spectroscopy is an instrumental method. | what is an instrumental method

Answer 27

-a method carried out using a machine

Question 28

explain how flame emission spectroscopy works:

Answer 28

a sample of metal ion in solution is placed into a flame the light given of by the flame is passed into a machine called a spectroscope. the spectroscope converts light into a line spectrum the position of the lines in the spectrum are specific for a given metal ion.

Question 29

the light given out from the flame is passed into a machine of called a spectroscope. what does a spectroscope do?

Answer 29

- when light given out from the flame is passed into a spectroscope, it converts the light into a line spectrum the position of the lines in the spectrum are specific for a given metal ion so we can use the line spectrum to identify the metal ion present.

Question 30

as well helping us identify the metal ions that are present. what else can flame emission spectroscopy show?

Answer 30

-the concentration of the metal ion because the line becomes more intense at a higher concentration

Question 31

what are the three advantages of using flame emission spectroscopy?

Answer 31

- rapid= flame emission spectroscopy can be used to analyse samples more rapidly than using flame tests - sensitive-flame emission spectroscopy will work on even a tiny sample of the metal compound - accurate- more likely to identify the metal ions correctly than using a flame test

Question 32

METAL HYDROXIDES- sodium hydroxide solution can be used to identify some metal ions which three metals form white precipitates when sodium hyddroxide solution is added to them:

Answer 32

-aluminium -magnesium -calcium ( memorise balanced equations for all of each metal nitrates reaction with sodium hydroxide eg aluminium nitrate+ sodium hydroxide= sodium nitrate+ aluminium hydroxide) the aluminium hydroxide is solid it is a precipitate

Question 33

how can we distinguish the white precipitates formed when reacting aluminium, magnesium and calcium with sodium hydroxide to identify the metal ions.

Answer 33

to identify if a precipitate has alumnium ions inside it, we can add excess sodium hydroxide and the precipitate should redissolve to work out which precipitate is calcium we must do a flame test.

Question 34

solutions of copper (ii) ions iron (iii) ions iron (ii) ions form coloured precipitates when sodium hydroxide is added. name the precipitates for each ion

Answer 34

copper (ii) ions= copper (ii) hydroxide blue precipitate iron (ii) ions hydroxide= green precipitate iron (iii) ions= iron (iii) hydroxide brown precipitate. (memorise balanced equations)

Question 35

testing FOR NON METAL IONS: testing for carbonates:

Answer 35

- add dilute acid to sample. - the dilute acid will react with the carbonate to make carbon dioxide gas we will see an effervscence (the fizzing does not prove the gas is co2). - now we bubble this gas through limewater. - if the limewater goes cloudy, then this will prove that we have co2.

Question 36

Testing for NON METAL IONS: hallide ions

Answer 36

1) add dilute nitric acid to the sample 2) add dilute silver nitrate solution 3) hallide ions produce precipitates of the silver halide 4) each hallid produces a different coloured precipitate

Question 37

name the coloured precipitates that each hallide ion produces when reacted with silver nitrate solution and nitric acid chloride ions bromide ions iodide ions

Answer 37

- chloride ions produce a white precipitate of silver chloride - bromide ions produce a cream precipitate of silver bromide - iodide ions produce a yellow precipitate of silver iodide

Question 38

testing for NON METAL IONS: sulfate ions

Answer 38

1) add dilute hydrochloric acid to a sample 2) add barium chloride solution 3) if sulfate ions present we will see a white precipitate

Question 39

specification points: 4.8.1.1 pure substances

Answer 39

in chemistry, a pure substance is a single element or compound not mixed with any other substance -pure elements and compounds melt and boil at specific fixed temperatures example of a pure substance in everyday language= a substance which has nothing added to it such as pure milk

Question 40

specification points 4.8.1.2 formulations

Answer 40

-A formulation is a complex mixture that has been designed as a useful product. formulations are made by mixing components in carefully measured quantities to ensure the product has the required properties examples of formulations- fuels, paints, cleaning products, alloys, fertilisers, medicines and foods

Question 41

specification points 4.8.1.3 Chromatography

Answer 41

chromatography can be used to separate mixtures and give information to help identify substances . chromatography involves the stationary phase ( paper) and the mobile phase (solvent) . separation depends on the distribution of substances between the phases. chemicals that are strongly attracted to the stationary phase will not move very far. chemicals that are weakly attracted to the stationary phase will move further up the paper. rf value- distance moved by solute/ distance moved by solvent different compounds have different rf values in different solvents which can be used to help identify the compounds. the compounds in a mixture may separate into different spots depending on the solvent but pure compounds will produce a single spot in all solvents.

Question 42

specification points 4.8.2.1 identifying gases 4. 8.2.2 4. 8.2.3 4. 8.2.4

Answer 42

-test for hydrogen= the test for hydrogen uses a burning splint held at open end of test tube of the gas. hydrogen burns rapidly with a squeaky pop sound -test for oxygen=the test for oxygen uses a glowing splint inserted into a test tube of gas. splint relights in oxygen test for carbon dioxide= the test for carbon dioxide uses an aqueous solution of calcium hydroxide (limewater) when carbon dioxide is shaken with or bubbled through limewater, limewater turns cloudy. test for chlorine=to test for chlorine use litmus paper. when damp litmus paper is put into chlorine gas, the litmus paper is bleached and turns white.

Question 43

specification points 4.8.3 identifying ions using flame tests and flame emission spectroscopy

Answer 43

Flame tests can be used to identify some metal ions (cations). Lithium, sodium, potassium, calcium and copper compounds produce distinctive colours in flame tests: • lithium compounds result in a crimson flame • sodium compounds result in a yellow flame • potassium compounds result in a lilac flame • calcium compounds result in an orange-red flame • copper compounds result in a green flame. If a sample containing a mixture of ions is used some flame colours can be masked.

Question 44

specification points: 4.8.3.6 instrumental methods

Answer 44

Elements and compounds can be detected and identified using instrumental methods. Instrumental methods are accurate, sensitive and rapid. Students should be able to state advantages of instrumental methods compared with the chemical tests in this specification.

Question 45

specification points- flame emission spectroscopy 4.8.3.7

Answer 45

Flame emission spectroscopy is an example of an instrumental method used to analyse metal ions in solutions. The sample is put into a flame and the light given out is passed through a spectroscope. The output is a line spectrum that can be analysed to identify the metal ions in the solution and measure their concentrations.

Question 46

specification points metal hydroxides 4.8.3.2

Answer 46

-sodium hydroxide solution can be used to identify some metal ions -solutions of aluminium, calcium and magnesium ions form white precipitates when sodium hydroxide solution is added. but only aluminium hydroxide precipitate dissolves in excess sodium hydroxide solution. -solutions of copper (ii) ions, iron (ii) ions and iron (iii) ions form coloured precipitates when sodium hydroxide solution is added. copper (ii) forms blue precipitate iron (ii) forms green precipitate iron (iii) forms brown precipitate

Question 47

specification points carbonates hallides and sulfates 4. 8.3.3 4. 8.3.4- 4. 8.3.5-

Answer 47

4.8.3.3-carbonates react with dilute acids to form carbon dioxide gas. carbon dioxide gas can be identified by limewater 4.8.3.4-hallide ions in solution produces precipitates with silver nitrate solution in the prescence of dilute nitric acid silver chloride is white precipitate silver bromide- cream precipitate silver iodide- yellow precipitate 4.8.3.5-sulfate ions in solution produce white precipitate with barium chloride solution in the presence of dilute hydrochloric acid