CHEMISTRY chem skills

Question 1

Why do substances have differing melting points?

Answer 1

The substance has a higher/lower melting/boiling point because more energy is required to overcome the
attraction

Question 2

what happens when a substance melt?

Answer 2

energy is needed to overcome the attractions between particles in the solid.

Question 3

What does a higher melting point mean?

Answer 3

there is more energy needed to overcome the attraction

Question 4

what does insoluble mean?

Answer 4

Unable to disolve

Question 5

What would slow evaporation do?

Answer 5

large crystals gained

Question 6

what is sieving and what does it do

Answer 6

separates different sized solids to remove smaller particles

Question 7

what method separates insoluble solids from liquids?

Answer 7

filtration

Question 8

What is needed to be done after filtration and why (2)

Answer 8

washing
- removes impurities
- ensures all product gets washed into filtrate

Question 9

What does evaporation do?

Answer 9

separates soluble solids form liquids

Question 10

when evaporating how do you form large crystals (2 steps)

Answer 10

by heating the solution to remove 2/3 of the solvent
then allowing it to slowly evaporate on a window ledge

Question 11

how do you ensure its completely dry (2 ways)

Answer 11

• continually heat until there is a change n mass
• leave to evaporate until there is no change in mass

Question 12

what does fractional distillation do

Answer 12

separates liquids with different boiling points from each other

Question 13

name 4 parts of fractional distillation

Answer 13

• round bottom flask
• leibig condenser
• condenser
• thermometer

Question 14

what is the residue in filtration

Answer 14

solid that gets stuck in the filter paper

Question 15

what is the filtrate in filtration

Answer 15

liquid that went through the filter paper

Question 16

name 5 labels of evaporation

Answer 16

• solvent vapour
• solution
• gauze
• evaporating basin
• heat

Question 17

define an atom

Answer 17

smallest building blocks of everything

Question 18

what is a substance made of only one type of atom

Answer 18

element

Question 19

what is a compound

Answer 19

two or more different atoms chemically bonded

Question 20

what is two or more atoms chemically bonded

Answer 20

molecule

Question 21

How many numbers on the periodic table?

Answer 21

118

Question 22

what is the small number on the periodic table

Answer 22

the atomic number (1-118)

Question 23

what is the big number on the periodic table

Answer 23

the mass number - the mass of atoms)

Question 24

what does the small number in formulars tell us

Answer 24

the amount of that atom present

Question 25

what do you call an element that only exist in pairs?

Answer 25

diatomic

Question 26

what are some examples of diatomic elements (3)

Answer 26

• H2
• 02
• Cl2

Question 27

what are the rules when naming substances

Answer 27

• non metals endings become ide
• mono=1oxygen,di=2 oxygen ,tri= 3 oxygen…
• when there are three or more elements with one being oxygen, ending changes to ate

Question 28

How do we identify whether its an acid by looking at the formular

Answer 28

Usually if it starts with H2 it is an acid ( e.g H2SO4 which is sulfuric acid)

Question 29

What is the word formular for the hydrogen balloon

Answer 29

hydrogen + oxygen -> water

Question 30

Name 6 signs that a reaction has occured

Answer 30

• change in temp
• change in colour
• sound
• solids left behind (precipitate)
• light
• change in smell/taste

Question 30

what are the three states and how do they move?

Answer 30

solid - slide past each other
liquid - small vibrations
gas - moves freely

Question 31

On a heating/cooling graph what do the straight lines show

Answer 31

the straight lines/ plateaus show a change in state

Question 31

What does changing in state require?

Answer 31

change in energy

Question 31

what is the non word equation for the hydrogen balloon

Answer 31

2H2 + 02 -> 2HO2

Question 32

How do we know when a substance is finished boiling

Answer 32

the temperature will rise

Question 32

what does chromatography do

Answer 32

separates soluble compounds

Question 33

what is the mobile and stationary phase in chromatography

Answer 33

mobile phase - the solvent
stationary phase - the chromatography paper

Question 33

In chromatography what do we draw the line in

Answer 33

pencil otherwise the pen ink will run, ruining the experiments

Question 34

what does the amount of movement in chromatography depend on (2 thing)

Answer 34

• the compounds affinity to the stationary phase
• the compounds affinity to the mobile phase

Question 34

Define affinity

Answer 34

how much it likes

Question 35

how many spots does a pure substance have compared to a mixture

Answer 35

a pure substance only has one spot whilst a mixture will have multiple

Question 36

What is the equation for rf

Answer 36

rf = distance of spot/distance of solvent

Question 37

define a pure substance

Answer 37

pure substance is a substance made of only one type of element or molecule ( doesn’t just have to be element)

Question 38

how do you show whether a substane is pure

Answer 38

check melting and boiling points - a pure substance should only have one melting or boiling point

Question 39

define a mixture

Answer 39

two or more compounds not chemically bonded

Question 40

define a formulation

Answer 40

a mixture with a purpose or fixed ratio ( e.g shampoo)