Chemical analysis (7) COPY

Question 1

what is a pure substance
a single element

Answer 1

a single element or compound not mixed with any other substance

Question 2

what is the definition of melting point

Answer 2

the temp when solid changes to liquid

Question 3

what is the definition of boiling point

Answer 3

the temp when liquid changes to gas

Question 4

what’s a mixture

Answer 4

two or more substances mixed together

Question 5

What are the melting and boiling points of pure substances described as?

Answer 5

sharp

Question 6

How do the melting and boiling points of impure substances compare to pure substances?

Answer 6

Impure substances do not have sharp melting or boiling points

Melting and boiling occur over a range of temperatures in impure substances.

Question 7

What effect do impurities have on the melting point of a solid?

Answer 7

Lower the melting point

Impurities disrupt the orderly structure of a solid, leading to a lower melting point.

Question 8

What effect do impurities have on the boiling point of a liquid?

Answer 8

Raise the boiling point

Impurities can increase the energy required for a liquid to boil.

Question 9

What can boiling and melting points be used for?

Answer 9

To distinguish substances from mixtures

Question 10

True or False: Impurities result in sharp melting and boiling points.

Answer 10

False

Impurities cause melting and boiling to occur over a range of temperatures.

Question 11

Fill in the blank: Impurities ______ the melting point of a solid.

Answer 11

lower

This is a key characteristic of how impurities affect solids.

Question 12

Fill in the blank: Impurities ______ the boiling point of a liquid.

Answer 12

raise

The presence of impurities can require higher temperatures for boiling.

Question 13

what is a formulation

Answer 13

a mixture that has been designed as a useful product

Question 14

three examples of formulations
MAF

Answer 14

• alloy
• medicine
• fertiliser

Question 15

what’s a mixture

Answer 15

two or more substances mixed together and usually easy to separate

Question 16

what does filtration separate

Answer 16

separates solids from a liquid

Question 17

what is the filtered solution called from filtration

Answer 17

filtrate

Question 18

label and what is this method called

Answer 18

filtration

Question 19

what does evaporation separate and an example

Answer 19

soluble solids from their solvent e.g. salt from salt water

Question 20

what does evaporation collect

Answer 20

the solid only

Question 21

what collects in evaporating dish after all water has evaporated when using the evaporation method

Answer 21

soluble solid

Question 22

definition of evaporation

Answer 22

change of state from liquid to gas when heated

Question 23

label and what method is this?

Answer 23

evaporation

Question 24

what will the product of crystallisation contain

Answer 24

water of crystallisation

Question 25

what method do we need when preparing our salts

Answer 25

crystallisation

Question 26

WHEN must we use crystallisation why can we not use evaporation

Answer 26

if the solid contains water of crystallisation

Question 27

what does simple distillation separate and an example

Answer 27

liquid from a solution e.g. water from salt solution

Question 28

what can we add to simple distillation to promote smooth boiling

Answer 28

anti-bumping granules

Question 29

what is distillation simply?

Answer 29

evaporation followed by condensation

Question 30

label and what method is this

Answer 30

simple distillation

Question 31

when water condenses what does it turn into?

Answer 31

back into a liquid

Question 32

what is a distillate

Answer 32

liquid collected in distillation

Question 33

what does fractional distillation separate

Answer 33

mixtures of miscible liquids that have different boiling points (liquids that mix together and have different boiling points)

Question 34

what are the distillates collected at different temperatures known as

Answer 34

fractions

Question 35

what is the difference between miscible liquids and immiscible liquids

Answer 35

miscible liquids mix immiscible liquids dont mix

Question 36

label and what is this method called

Answer 36

fractional distillation

Question 37

what does paper chromatography separate

Answer 37

separates a mixture of soluble substances dissolved in a solvent e.g. colouring agents in foods/dyes/inks

Question 38

which has a lower melting point; a pure or impure substance

Answer 38

impure

Question 39

what is the method for paper chromatography

Answer 39

- draw pencil base line - use capillary tube, place a concentrated spot of substance on line - place paper in beaker with solvent at bottom - allow solvent to travel up paper - when solvent is near top, take paper out + mark where reached - dry - different compounds are shown as different spots

Question 40

how do we identify the separated components of a mixture when using chromatography paper

Answer 40

Rf - retardation factor

Question 41

how do we work out Rf

Answer 41

distance moved by spot/distance moved by solvent

Question 42

What does Rf value indicate?

Answer 42

The Rf value indicates the retention factor of a substance in a solvent.

Question 43

Is the Rf value of a particular substance in the same solvent always the same?

Answer 43

Yes, the Rf value is always the same for a particular substance in the same solvent.

Question 44

How can Rf values be used in assessing purity?

Answer 44

Rf values can be used to assess purity by comparing the Rf value of a substance to that of a pure substance.

Question 45

True or False: An impure substance will have the same Rf value as a pure substance.

Answer 45

False.

Question 46

Fill in the blank: An impure substance will have a _______ Rf value from a pure substance.

Answer 46

different

Question 47

why must the base line be drawn in pencil when using chromatography paper

Answer 47

pen would dissolve and interfere with results