Elements, Compounds And Mixtures

Question 1

What tells us the element?

Answer 1

The number of protons

Question 2

What is an element?

Answer 2

A substance formed from one type of atom
(Can’t be split into anything simpler)

Question 3

What is a compound?

Answer 3

A substance formed from two or more different atoms chemically combined/bonded together
(In fixed proportions)

Question 4

What is a molecule?

Answer 4

Two or more atoms held together by chemical bonds
—> can’t contain different elements

Question 5

What does pure mean?

Answer 5

When you have just one element or compound
(No other substance is present)

Question 6

What does impure mean?

Answer 6

When an element or compound is mixed with small amounts of other substances (impurities)

Question 7

What is the difference between Co and CO

Answer 7

Co: an element (cobalt)
CO: a compound (carbon monoxide)

Question 8

Pure substances have a …

Answer 8

Sharp melting/boiling point

Question 9

What temperature does pure water melt at?

Answer 9

0 degrees celsius

Question 10

What temperature does pure water boil at?

Answer 10

100 degrees celsius

Question 11

What happens to the melting point of a substance if an impurity is present?

Answer 11

It decreases and is not sharp
Salty water may start melting at -5 and finish melting at -2

Question 12

What happens to the boiling point of a substance if an impurity is present?

Answer 12

Increases
Salty water might boil at 103 degrees celsius

Question 13

How could you confirm whether a substance is pure or impure?

Answer 13

Measure its melting or boiling point
Pure substances have fixed, sharp melting/boiling points

Question 14

What is a mixture?

Answer 14

Two or more substances not chemically combined together

Question 15

What can compounds only be separated into elements by?

Answer 15

Chemical changes

Question 16

Why are mixtures easy to separate using physical processes?

Answer 16

Because they are not chemically combined

Question 17

What are some separation techniques?

Answer 17

Filtration
Crystallisation
Evaporation
Distillation
Fractional distillation
Chromatography

Question 18

What is filtration used for?

Answer 18

To separate an insoluble solid from a liquid
- the insoluble solid cannot pass through the filter paper but the liquid molecules can

Question 19

What equipment is used in filtration?

Answer 19

Conical flask
Filter funnel
Filter paper
Beaker (to hold the mixture before separating)

Question 20

What is crystallisation used for?

Answer 20

To separate a dissolved solid (soluble solid) from a solution

Question 21

Steps for crystallisation

Answer 21

1) heat the solution
2) when some of the solvent evaporates and crystals start forming in the solution you stop heating it and leave it to cool
—> more crystals will start to form
3) filter out these crystals from the remaining solution
4) dry these crystals (in a sunny area or a dry oven)

Question 22

What equipment is used in crystallisation?

Answer 22

Tripod
Gauze
Bunsen burner
Evaporating dish

Question 23

What is evaporation used for?

Answer 23

To separate a dissolved solid (soluble solid) from a solution

Question 24

Steps for evaporation

Answer 24

1) heat the solution
2) the solvent will start to evaporate (the remaining solution is more concentrated)
3) crystals will start to form because it is so concentrated
4) eventually all the solvent will evaporate leaving dry crystals of our solid

Question 25

Pros and cons of evaporation

Answer 25

Pros: quick and easy Cons: some solids decompose when heated (thermal decomposition) —> solid will be broken down into something else

Question 26

What equipment is used in evaporation?

Answer 26

Tripod Gauze Bunsen burner Evaporating dish

Question 27

What is distillation used for?

Answer 27

To separate a pure liquid from a solution

Question 28

Steps for distillation

Answer 28

1) heat the solution 2) the pure liquid will boil and evaporate 3) as it rises to the top of the flask the pressure will force it down the condenser 4) the vapour will cool it down and condense into liquid form 5) it will run down the pipe and collect in the beaker

Question 29

What equipment is used in distillation

Answer 29

Thermometer Gauze Tripod Anti-bumping granules Bunsen burner Round-bottom flask Condenser Clamp stand Beaker

Question 30

What is fractional distillation used for?

Answer 30

To separate a pure liquid from a mixture of liquids

Question 31

Steps for fractional distillation

Answer 31

1) heat the mixture 2) when temp reaches the boiling point of one of the liquids it will evaporate and rise up the fractionating column 3) it will then pass into the condenser and condense back into the liquid and collect into the beaker 4) repeat for each liquid’s boiling point

Question 32

What is the fractionating column used for?

Answer 32

To help separate liquids with similar boiling points

Question 33

What equipment is used in fractional distillation?

Answer 33

Thermometer Gauze Tripod Bunsen burner Round-bottom flask Fractionating column Condenser Clamp stand Beakers

Question 34

What is chromatography used for?

Answer 34

To separate a mixture of different dyes in an ink (or dissolved substances)

Question 35

Chromatography results

Answer 35

1) each substance will travel a different distance up the paper depending on how soluble it is in the solvent 2) the most soluble substances travel the furthest

Question 36

What is the stationary phase?

Answer 36

The paper that the substances move on Molecules can’t move

Question 37

What is the mobile phase?

Answer 37

The liquid (solvent) that moves through the paper carrying the substances Molecules can move

Question 38

In chromatography what depends on how far each of the substances travel?

Answer 38

Their properties

Question 39

What equipment is used in chromatography?

Answer 39

Lid Beaker Filter/chromatography paper

Question 40

Equation for Rf value

Answer 40

Distance travelled by the spot —————————————— Distance travelled by the solvent

Question 41

What does it mean if two sports have the same Rf value?

Answer 41

They are probably the same chemical

Question 42

What will a pure substance do on a chromatogram?

Answer 42

It won’t separate at all (Stay a single spot)

Question 43

What would happen if your repeated the chromatography experiment but with a different solvent or paper?

Answer 43

The chromatogram might look different —> Rf value would be different too because we would have changed the stationary or mobile phase

Question 44

What are correctly calculated Rf values always between?

Answer 44

0.00 and 1.00

Question 45

What is one safety precaution you should take when carrying out the method to separate a soluble solid from a solution (evaporation/crystallisation)

Answer 45

Do not allow it to boil dry

Question 46

What are anti-bumping granules?

Answer 46

Small glass granules added to a liquid to help it boil smoothly during distillation

Question 47

What temperature does steam condense at?

Answer 47

100 degrees celsius

Question 48

What is the name to the solid that collects in the filter paper?

Answer 48

Residue

Question 49

What is the name given to the liquid that passes through a filter paper?

Answer 49

Filtrate

Question 50

What term describes the highest point reached by the solvent on a chromatogram?

Answer 50

Solvent front

Question 51

What should you use for drawing the baseline on a chromatogram?

Answer 51

Pencil Graphite is insoluble solid won’t run up the paper and interfere with the results

Question 52

How deep into the solvent should you place the paper when starting a chromatography experiment?

Answer 52

The bottom of the paper must be under the solvent but the baseline and spots must be above the solvent