CHEMISTRY chem skills Flashcards

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1
Q

Why do substances have differing melting points?

A

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

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2
Q

what happens when a substance melt?

A

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

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3
Q

What does a higher melting point mean?

A

there is more energy needed to overcome the attraction

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4
Q

what does insoluble mean?

A

Unable to disolve

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5
Q

What would slow evaporation do?

A

large crystals gained

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6
Q

what is sieving and what does it do

A

separates different sized solids to remove smaller particles

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7
Q

what method separates insoluble solids from liquids?

A

filtration

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8
Q

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

A

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

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9
Q

What does evaporation do?

A

separates soluble solids form liquids

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10
Q

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

A

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

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11
Q

how do you ensure its completely dry (2 ways)

A
  • continually heat until there is a change n mass
  • leave to evaporate until there is no change in mass
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12
Q

what does fractional distillation do

A

separates liquids with different boiling points from each other

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13
Q

name 4 parts of fractional distillation

A
  • round bottom flask
  • leibig condenser
  • condenser
  • thermometer
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14
Q

what is the residue in filtration

A

solid that gets stuck in the filter paper

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15
Q

what is the filtrate in filtration

A

liquid that went through the filter paper

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16
Q

name 5 labels of evaporation

A
  • solvent vapour
  • solution
  • gauze
  • evaporating basin
  • heat
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17
Q

define an atom

A

smallest building blocks of everything

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18
Q

what is a substance made of only one type of atom

A

element

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19
Q

what is a compound

A

two or more different atoms chemically bonded

20
Q

what is two or more atoms chemically bonded

A

molecule

21
Q

How many numbers on the periodic table?

A

118

22
Q

what is the small number on the periodic table

A

the atomic number (1-118)

23
Q

what is the big number on the periodic table

A

the mass number - the mass of atoms)

24
Q

what does the small number in formulars tell us

A

the amount of that atom present

25
Q

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

A

diatomic

26
Q

what are some examples of diatomic elements (3)

A
  • H2
  • 02
  • Cl2
27
Q

what are the rules when naming substances

A
  • 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
28
Q

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

A

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

29
Q

What is the word formular for the hydrogen balloon

A

hydrogen + oxygen -> water

30
Q

Name 6 signs that a reaction has occured

A
  • change in temp
  • change in colour
  • sound
  • solids left behind (precipitate)
  • light
  • change in smell/taste
30
Q

what are the three states and how do they move?

A

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

31
Q

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

A

the straight lines/ plateaus show a change in state

31
Q

What does changing in state require?

A

change in energy

31
Q

what is the non word equation for the hydrogen balloon

A

2H2 + 02 -> 2HO2

32
Q

How do we know when a substance is finished boiling

A

the temperature will rise

32
Q
A
32
Q

what does chromatography do

A

separates soluble compounds

33
Q

what is the mobile and stationary phase in chromatography

A

mobile phase - the solvent
stationary phase - the chromatography paper

33
Q

In chromatography what do we draw the line in

A

pencil otherwise the pen ink will run, ruining the experiments

34
Q

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

A
  • the compounds affinity to the stationary phase
  • the compounds affinity to the mobile phase
34
Q

Define affinity

A

how much it likes

35
Q

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

A

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

36
Q

What is the equation for rf

A

rf = distance of spot/distance of solvent

37
Q

define a pure substance

A

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

38
Q

how do you show whether a substane is pure

A

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

39
Q

define a mixture

A

two or more compounds not chemically bonded

40
Q

define a formulation

A

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