chemical analysis

Question 1

what is a pure substance

Answer 1

one single substance containing one type of chemical

Question 2

what is a mixture

Answer 2

more than one substance that are not chemically bonded

Question 3

what is a formulation

Answer 3

a mixture that has been designed

Question 4

what are the 6 methods of separation

Answer 4

filtration, evaporation, crystallisation, simple distillation, fractional distillation, chromatography

Question 5

explain the separation process of filtration

Answer 5

solid from a liquid
use filter paper

Question 6

explain the separation process of evaporation

Answer 6

separate a solid from a soluble
using heat

Question 7

explain the separation process of crystallisation

Answer 7

producing solid crystals from a solution
use an evaporating dish

Question 8

explain the separation process of simple distillation

Answer 8

separating a solvent from a solution
using a condensing tube

Question 9

explain the separation process of fractional distillation

Answer 9

separate a solvent from a mixture of two or more liquids
condensing tube

Question 10

explain the separation process of chromatography

Answer 10

separating disolved substances from one another
ink dyes
using chromatography paper

Question 11

how does chromatography work

Answer 11

the solvent runs up the filter paper and the different chemicals separate out as they interact with the paper differently. some ink will bond more strongly than others

Question 12

what is the calculation for an Rf value

Answer 12

distance travelled by substance divided by distance travelled by solvent

Question 13

what are the four common gasses we test for

Answer 13

chlorine, oxygen, carbon dioxide, hydrogen

Question 14

how do we test for chlorine and what are the results

Answer 14

place blue litmus paper in a test tube with the gas - if there is chlorine present the paper will turn from blue to red to white

Question 15

how do we test for carbon dioxide and what are the results

Answer 15

bubble the gas through limewater - it will turn cloudy if co2 is present

Question 16

how do we test for hydrogen and what are the results

Answer 16

a glowing splint into a test tube with the gas, if it makes a squeaky pop, hydrogen is present

Question 17

how do we test for oxygen and what are the results

Answer 17

a glowing splint into a test tube with gas inside, if oxygen is present, splint will relight

Question 18

when testing for ions why does the colour of the flame change

Answer 18

when heating, the electrons gain thermal energy, when these electrons return to lower energy levels, they emit the excessive energy as light

Question 19

what are the flame colours for each ion testing

Answer 19

lithium - red
sodium - orange/yellow
potassium - purple
calcium - orange
copper - green

Question 20

what are the negatives of using the normal flame testing method

Answer 20

hard to determine colour as they can be similar
samples can contain multiple metals and therefore colours mix

Question 21

what is flame emission spectroscopy

Answer 21

a method of flame testing that uses a spectroscope which detects the individual wavelengths of light that is emoted

Question 22

how do we identify the ion when using emission spectroscopy

Answer 22

the unique line spectrum that each metal ion produces

Question 23

along with solving the problems that normal flame testing, what other benefit does flame spectroscopy have

Answer 23

the intensity of the lines on the wavelength depict how concentrated the ion is

Question 24

how can we use flame emission spectroscopy to test for unknown ions

Answer 24

when looking at the line spectra for the unknown sample, we can compare it to know metal ions to see which ions are contained in the unknown sample

Question 25

compare the use of manual flame testing and instrumental methods

Answer 25

manual - basic and cheap

instrumental - more expensive but more accurate
- very sensitive ( detect tiny amounts)
- very fast (don’t need a human)

Question 26

what is an anion

Answer 26

negatively charged ions

Question 27

what forms when you react a carbonate with an acid

Answer 27

salt, carbon dioxide gas and water

Question 28

how do you test for a carbonate ion and what is the results

Answer 28

• add dilute hydrochloric acid to the test sample and take any gas that is produced and bubble through lime water to test for carbon dioxide
• if limewater turns cloudy, a carbonate was present

Question 29

what forms when you react barium ions to sulphate

Answer 29

a white precipitate

Question 30

how do you test for for sulphate ions and results

Answer 30

• take a sample and add dilute hydrohalic acid which removes any carbonate or sulphite ions ( these ions can also react with barium )
• add barium chloride solution
  white precipitate will form

Question 31

what are the three halide ions we test for

Answer 31

chloride ions, bromide ions and iodide ions

Question 32

how do you test for halide ions and results for each ions

Answer 32

• add dilute nitric acid to get rid of impurities
• add silver nitrate (silver ions will react with halide ions and form precipitate)

chloride - silver chloride - white precipitate
bromide - silver bromide - cream precipitate
iodide - silver iodide - yellow precipitate