Chemical Analysis

Question 1

What is and element?

Answer 1

A substance containing only 1 type of atom

Question 2

What is a compound?

Answer 2

A substance containing atoms of different elements chemically joined together

Question 3

What is a mixture?

Answer 3

A substance that contains more than one substance (not chemically joined) and easily separated using a physical property, EG WATER or AIR

Question 4

Test and result for Hydrogen? (H2)

Answer 4

A lit splint placed in gas causes squeaky pop.

Question 5

Test and result for Oxygen? (O2)

Answer 5

Glowing splint placed in gas re-ignites

Question 6

Test and result for Carbon Dioxide? (CO2)

Answer 6

Bubble gas into limewater and it turns cloudy

Question 7

Test and result for water. (H2O)

Answer 7

White anhydrous CuSO4 turns blue when water is added.

Question 8

What is the definition for Pure Substances?

Answer 8

This substance is a single element or compound. In everyday language, a pure substance can mean a substance that has nothing added to it, so it is unadulterated and in its natural stage, eg pure milk.

Question 9

What boiling and melting points do pure substances have?

Give an example.

Answer 9

They have fixed melting and boiling points.
Distilled water:
Melting point: 0 degrees C
Boiling point: 100 degrees C

Question 10

What boiling and melting points do impure substances have?

Give an example.

Answer 10

They have a range of melting points and boiling points
Brine (salt water)
Melting point: -5 - -10 degrees C
Boiling point: 101 - 103 degrees C

Question 11

What will impurities do to the melting and boiling points?

Answer 11

• Reduce the melting point and increases the melting point range.
• Increases the boiling point and give a range

Question 12

What is a formulation?

Answer 12

A mixture of specific quantities/ratios designed as a useful product. Each component is present in a measured quantity and contributes to the properties of the formulation. e.g paint, cake mix, fuels, drugs, fertilisers.

Question 13

What makes up Brass? (include percentages and uses)

Answer 13

70% Copper
30% Zinc
USES
musical instruments (doesn’t corrode)

Question 14

What makes up Bronze? (include percentages and uses)

Answer 14

95% Copper
5% Tin
USES
statues, church bells (strong, doesn’t corrode, makes ringing noise)

Question 15

What makes up Stainless Steel? (include and uses)

Answer 15

Iron
Nickel
Chromium
USES
medical equipment, cutlery, chemical plants (doesn't rust)

Question 16

What example of a formulation do farmers uses and what do they contain?

Answer 16

Fertilisers - farmers use NPK fertilisers: Nitrogen, phosphorous, and potassium of varying quantities based on what is needed to be returned to the soil.

Question 17

Why in a chromatography experiment is the base line drawn in pencil?

Answer 17

Pencil is graphite - this is insoluble and will not dissolve in the solvent and will not interfere with the experiment.

Question 18

Why in a chromatography experiment is the base line above the solvent?

Answer 18

Samples on the base line must be above the solvent to start with, or they would dissolve in the solvent.

Question 19

Why in a chromatography experiment samples must be placed on the base line?

Answer 19

To give a fixed point for measuring the distance they have moved.

Question 20

Why in a chromatography experiment should a lid be put on the equipment?

Answer 20

To stop solvents evaporating if they have a low boiling point.

Question 21

What should you remember when reading a chromatogram?

Answer 21

• The number of spots above each letter, tells you how many pigments there are in the mixture.
• If the pigments have travelled the same distance, they may be the same pigment.

Question 22

What is the formula for calculating the Rf value?

Answer 22

Rf value = distance moved by substance / distance moved by solvent front

Question 23

How can compounds be identified using Rf value?

Answer 23

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 a pure compound will produce a single spot in all solvents.

Question 24

What is the Stationary phase?

Answer 24

the piece of chromatography paper (molecules that cannot move)

Question 25

What is the Mobile phase?

Answer 25

the solvent (molecules can move either liquid or gas) eg water or ethanol

Question 26

Descibe how you carry out the chromatography experiment?

Answer 26

1) Use a ruler to draw a horizontal pencil line 2cm from the bottom of the chromatography paper 2) mark five pencil spots at equal intervals across the origin line 3) using a different capillary tube for each coloring, put a small spot of each colouring on four of the pencil spots 4) Use another capillary tube to put a small spot of the unknown mixture on the last pencil spot 5) pour water into the beaker to a depth no more than 1cm 6) clip the top of the paper to a wooden spill and rest on top of beaker. The bottom of the paper should dip in the solvent 7) wait for the water solvent to travel at least 3/4 of the way up the paper 8) remove the paper from the beaker and draw another pencil line as close to the wet edge as possible, this is the solvent front line 9) hang the paper up to dry thoroughly

Question 27

How does chromatography work?

Answer 27

1) mixture dissolves in the mobile phase as it moves through the stationary phase 2) the mixture is also interacting with the stationary phase (constantly switiching between phases) 3) the more soluble a component of the mixture, the further it will travel 4) different components have different Rf values

Question 28

Why do different substances travel different distances up the chromatography paper?

Answer 28

- substances that have a stronger attraction to the solvent (more soluble), move quickly and travel a long way up the paper - substances that have a stronger attraction to the paper, move slower and travel a short distance up the paper

Question 29

What does a large Rf value indicate?

Answer 29

- the substance is very soluble | - the substance spent a longer time in the mobile phase

Question 30

Why would a permanent marker have an Rf value of 0?

Answer 30

Because they are insoluble so don't dissolve in the solvent and travel up the paper

Question 31

How can a more reliable result be given for chromatography experiments?

Answer 31

- repeating the experiment using a different solvent - calculate the different Rf values and compare with the previous Rf value - the Rf values should match relative to the other substances

Question 32

How can paper chromatography be used to identify what impurity is present in the substance/mixture

Answer 32

- run the mixture alongside pure samples of the possible impurity - if the spot from one of the possible impurities moves the same distance as the mixture, then it indicates that that is the impurity - this is the same if the calculated Rf values match

Question 33

What is the colour of the flame for lithium testing?

Answer 33

crimson

Question 34

What is the colour of the flame for sodium testing?

Answer 34

yellow

Question 35

What is the colour of the flame for potassium testing?

Answer 35

lilac

Question 36

What is the colour of the flame for calcium testing?

Answer 36

orange-red

Question 37

What is the colour of the flame for copper testing?

Answer 37

green

Question 38

What are the limitations to the flame tests?

Answer 38

- it is diffucult to judge the colour - individuals see colour differently - results quoted (expected flame colours) are only for pure substances - if a mixture of ions is in the flame test, they can mask the colour of one ion

Question 39

What is the test and result for chlorine?

Answer 39

add damp litmus paper to the gas and if chlorine, it bleaches the paper white