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O Levels > CHEMISTRY > Flashcards

CHEMISTRY Flashcards

1
Q

When reading the volume of a liquid, how should we position our eyes?

A

At the MENISCUS
-to avoid parallax error.

Meniscus = the curve formed at the surface of the liquid in a container.

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2
Q

What apparatus is used to measure the VOLUME OF A GAS?

A

Gas Syringe

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3
Q

What is concave and convex?

A

Concave (upward curving)
Convex (downward curving)

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4
Q

What are the 4 apparatus used to measure VOLUME OF LIQUID and what is its accuracy?

A
  1. [PIPETTE] whole numbers

-Measures accurate fixed volumes, 10.0 cm3 or 25.0 cm3.

  1. [VOLUMETRIC FLASK] large numbers

-Measures accurate fixed volumes that are larger, 100 cm3 or 250 cm3.

  1. [MEASURING CYLINDER] 1d.p range

-Measures a range of volumes to the nearest 0.5 cm3, 31.5 c,3 or 23.0 cm3.

  1. [BURETTE] 2d.p range

-Meausres a range of volumes to the nearest .05 cm3, 31.55 cm3 or 23.00 cm3.

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5
Q

(2) The method used to collect a gas depends on the following physical properties of the gas:

A
  1. Solubility:
    how easily the gas dissolves in water.
  2. Density:
    how dense the gas is compared to the surrounding air (28).
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6
Q

(3) What methods are used to collect greater volumes ofGASES?
What are their solubility, density?
List examples each.

A
  1. [WATER DISPLACEMENT]
    Solubility: Insoluble to slightly soluble
    Density of gas: Density does not affect gas collection.
    E.g: Hydrogen, Oxygen, Carbon Dioxde.
  2. [DOWNLOAD DELIVERY]
    Solubility: Soluble or insoluble
    Density of gas: Denser than air
    E.g: Chlorine, Hydrogen Chloride, Sulfur Dioxide
  3. [UPWARD DELIVERY’]
    Solubility: Soluble or insoluble
    Density of gas: Less dense than air
    E.g: Ammonia
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7
Q

Name 3 separation techniques for SOLID-SOLID mixture.

A
  1. Magnetic attraction
  2. Sieving
  3. Using suitable solvents
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8
Q

Name 4 separation techniques used for SOLID-LIQUID mixture.

A
  1. Filtration
  2. Evaporation to dryness
  3. Crytallisation
  4. Simple distillation
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9
Q

Name 2 separation technques used for LIQUID-LIQUID mixture.

A
  1. Paper Chromatography
  2. Fractional Distillation
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10
Q

What method is used to obtain salt from seawater?

A

EVAPORATION TO DRYNESS

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11
Q

Name the steps on how to obtain pure copper (II) sulfate crystals by CRYSTALLISATION.

A
  1. Gently heat the copper (II) sulfate solution in an evaporating dish to evaporate most of the liquid, until the solution is saturated.
    -Stop heating the solution before all the solvent has evaporated.
  2. Cool the solution gradually until the solid copper (II) sulfate crystals appear within the solution.
  3. Carefully pour the mixture (solution with the crystals) through a funnel lined with filter paper to collect the solid crystals. If more crytstals are required, the filtrate is re-concentrated and re-crystallised (repeat steps 1 to 3)
  4. The copper (II) sulfate crystals are washed with some cold distilled water to remove impurities. They can be dried between a few sheets of filter paper.
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12
Q

What is boiling chip’s function in Simple Distillation?

A

Smooth boiling

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13
Q

In the reactivity series, how are metals arranged?

A

MOST reactive to LEAST reactive

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14
Q

The order of reactivity of metals can be determined by the REACTIONS of metals with:

A
  1. Cold Water (hydroxide)
  2. Steam (water, gaseous, oxide) [higher temp. = more thermal energy]
  3. Dilute hydrochloric acid
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15
Q

(12) MOST REACTIVE metals to LEAST REACTIVE metals

A

P-Potassium
S-Sodium
C-Calcium
M-Magnesium
A-Aluminium
Z-Zinc
I-Iron
L-Lead
H-Hydrogen
C-Copper
S-Silver
G-Gold

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16
Q

Reaction of metals with COLD WATER.
Give an example of magnesium in water

A

[METAL + WATER -> METAL HYDROXIDE + HYDROGEN]

(E.g) Mg:
Magnesium + Water -> Magnesium Hydroxide + Hydrogen

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17
Q

Reaction of metals with STEAM.
Give an example of Zinc in steam.

A
  1. Some metals such as zinc and iron react with steam instead of cold water.
  2. More reactive metals react more violently with steam.

[METAL + STEAM -> METAL OXIDE + HYDROGEN]

(E,g) Zn:
Zinc + Steam -> Zinc Oxide + Hydrogen
Zn (s) + H20 (g) -> ZnO (s) + H2 (g)

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18
Q

Reaction of metals with DILUTE HYDROCHLORIC ACID.

A
  1. METAL + DILUTE HYDROCHLORIC ACID -> METAL CHLORIDE + HYDROGEN
  2. Metals above hydrogen in the reactivity series react with hydrochloric acid.
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19
Q

Which 3 metals ‘occurs no reaction’ when with DILUTE HYDROCHLORIC ACID?

A
  1. Lead
  2. Copper
  3. Silver
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20
Q

Which acids does Lead react and not react with?

A

Lead ONLY reacts with NITRIC ACID.

-It does not appear to react with HYDROCHLORIC ACID and SULFURIC ACID.

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21
Q

How can we deduce the order of reactivity of metals (in terms of SOLUTION)?
Give an example.

A

A MORE REACTIVE metal can displace a LESS REACTIVE from its salt solution.

(E.g):
-Iron is more reactive than copper and displaces copper from aqueous copper (II) sulfate.

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22
Q

What is the equation of Iron in Copper (II) Sulfate solution.

A

Iron + Copper (II) Sulfate -> Iron (II) Sulfate + Copper

[grey metal] Fe (s) + [blue solution] CuSO4 (aq) -> [green solution] FeSO4 (aq) + [reddish brown] Cu (s)

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23
Q

What has been observed from Iron in Copper(II) Sulfate solution?

Observed= what you see, colour change (initial colour to final colour)

A
  1. Blue solution
  2. Reddish Brown deposit observed (on grey metal).
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24
Q

(7) Appearance of metals and its salt solution: Color and Inference

A

COLORLESS solution- Salt solution of potassium, sodium, ammonium, zinc, aluminium or calcium

BLUE solution (due to Copper2+)- Copper (II) salts (e.g copper (II) sulfate)

GREEN solution (due to Iron2+)- Iron (II) salts (e.g. iron (II) sulfate)

YELLOW or BROWN solution- Iron(III) salts (e.g iron (III) chloride or iron (III) sulfate)

REDDISH BROWN/PINKISH BROWN solid- Copper

GREY solid- Other metals (Iron fillings, Zinc Powder, magnesium POwder)

BLACK solid- Copper (II) oxide

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25
Q

How can we deduce the order of reactivity of metals (in terms of SOLID)?
Give an example.

A
  1. A more reactive metal will displace a less reactive metal from its ocide.

(E.g):
Zinc is MORE REACTIVE than copper. It displaces copper in copper (II) oxide.

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26
Q

What happens if the displacement reaction is repeated using ZINC OXIDE and COPPER, instead of ZINC with COPPER(II) OXIDE?
Explain.

A

There is no visible reaction as copper is less reactive than zinc.
Thus, copper cannot displace zinc from its oxide.

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27
Q

(2) What are the conditions for rusting?

A

Water and Oxygen

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28
Q

Explain RUSTING.

A

(Only Iron rusts, other metals corrode.)

  1. When an iron object is left in DAMP AIR for a while, a RED-BROWN material gradually develops on the metal’s surface.
    =Rust/ Hydrated Iron (III) oxide

[Iron+ Oxygen + Water -> Hydrated Iron (III) Oxide <rust>]</rust>

  1. Sodium Chloride increases the rate of rusting.
    (Acidic substances such as carbon dioxide and sulfur dioxide SPEED UP rusting.)
  2. Iron objects near the sea corrode quickly due to the presence of SALT and other pollutants in the air.
  3. Rust is exceedingly flaky and brittle.
    -As iron corrodes, the metal’s rusted surface flakes off.
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29
Q

How to PREVENT rusting? Give 5 ways.

A

Barrier Methods (protective layer)
-Barrier methods keep oxygen and water away from the iron or steel.

(E.g):
1. Painting
2. Oiling or greasing
3. Plastic coating
4. Tin-plating
5. Chrome-plating

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30
Q

What is sacrificial protection?

A
  1. Other metals also require water and oxygen to corrode.
  2. However, the metal forms a protective oxide layer after reacting, preventing further corrosion.

-For metals that are more reactive than iron such as magnesium and zinc.

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31
Q

Why does the solvent level must be lower than the starting line where the samples are placed? (Paper Chromatography)

A

To ensure that the ink sample does not dissolve in the solvent and does not separate.

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32
Q

(1) Advantage of using chromatography to identify the unknown components in a mixture

A
  1. Able to identify the purity of a substance.
    -Only a small amount of sample is needed to do chromatography.
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33
Q

Why does the temperature remains CONSTANT during melting?

A

During melting, thermal energy absorbed by the solid particles is used to break the attracted forces between the particles, instead of raising the temperature.

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34
Q

In terms of Kinetic Particle Theory, explain what happens to the particles during melting.

A
  1. The solid particles vibrate at fixed positions and are packed closely together in an orderly arrangement.
  2. On further heating, the solid particles gain heat energy and move around more quickly.
  3. Eventually, the solid particles have sufficient energy to break the forces holding them together to become a liquid.
  4. The liquid particles are now slightly further apart (but still closely packed) in a disorderly arrangement. They are able to move throughout the liquid.
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35
Q

Why does the temperature remains constant during boiling?

A

During boiling, heat energy absorbed by the liquid particles is used to break the attracted forces holding the particles together, instead of raising the temperature.

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36
Q

In terms of Kinetic Particle Theory, explain what happens to the particles during boiling.

A
  1. The liquid particles are packed closely together in a disorerly arrangement. They are only able to move throughout the liquid.
  2. On further heating, the liquid particles gain heat energy and move around more quickly.
  3. Eventually, the liquid particles have sifficient energy to break the forces holding them together to become a gas.
  4. The gas particles are now far apart in a random arrangement. They are able to move freely in the container.
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37
Q

(2) Differences between Evaporation vs. Boiling

A

[Evaporation]
-Occurs at ALL temperatures
-Occurs only at the surface of the liquid

[Boiling]
-Occurs only at the boiling point
-Occurs throughout the liquid

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38
Q

Why does the temperature remain constant during CONDENSATION?

A

During condensation, thermal energy released by the gas particles is used to form attracted forces between the particles, instead of lowering the temperature.

39
Q

In terms of Kinetic Particle Theory, explain what happens to the particles during condensation.

A
  1. The gas particles are far apart and in a random arrangement. They are able to move freely in the container.
  2. On further cooling, the gas particles lose heat energy and move around more slowly.
  3. Eventually, the gas particles form bonds between themselves and become closer together to become a liquid.
  4. the liquid particles are now packed closely together in a disorderly arrangement. They are able to move throughout the liquid.
40
Q

Why does the temperature remain constant during freezing?

A

During freezing, heat energy released by the liquid particles is used to form attracted forces between the particles, instead of lowering the temperature.

41
Q

In terms of Kinetic Particle Theory, explain what happens to the particles during freezing.

A
  1. The liquid particles are packed closely together in a disorderly arrangement. They are only able to move throughout the liquid.
  2. On further cooling, the liquid particles lose heat energy and move around more slowly.
  3. Eventually, the liquid particles form bonds between themselves and become closer together to become a solid.
  4. The solid particles are now packed closely together in an orderly arrangement. They are only able to vibrate at fixed positions.
42
Q

What is sublimation?
Give 4 examples.

A

The process whereby a substance changes from a solid to a gas directly, without going through the liquid state.

(E.g):
-Dry Ice (Solid Carbon Dioxide)
-Iodine Crystals
-Napthalene (Mothballs)
-Ammonium Chloride

43
Q

What is vapour deposition?
Give 1 example.

A

The process whereby a substance changes from a gas to a solid directly.

(E.g):
Iodine Crystals (when it comes into contact with a cold glass surface).

44
Q

(4) What are characteristics of Atoms?

A
  1. Atoms are electrically neutral.
  2. No. of protons = No. of electrons.
  3. Protons and neutrons are in the nucleus, hence they are NUCLEONS.
  4. Electrons are found in electron shells found away from the nucleus.
45
Q

What is the Relative MASS and CHARGE of sub-atomic particles?

A

[Relative Mass]
Proton: 1
Neutron: 1
Electron: 1/1840

[Relative Charge]
Proton: +1
Neutron: 0
Electron: -1

[Location in Atom]
Proton: Nucleus
Neutron: Nucleus
Electron: Electron Shell

46
Q

What are radioactive isotopes?

A

Radioactive isotopes are unstable forms of an element. They release radiation when they break down to become more stable.

46
Q

What are ISOTOPES?

A

Atoms of the same element that have the same proton (atomic) number but nucleons (mass) numbers.

46
Q

What are Elements, Compound, Mixture made of?

A

Element: Only one element

Compound: Two or more elements that are chemically combined IN A FIXED RATIO

Mixture: Two or more elements and/or compound that are NOT chemically combined.

47
Q

How are Elements, Compound, Mixture formed?

A

Elements: Most naturally occurring

Compound: From a chemical reaction

Mixture: Usually from physical mixing

48
Q

What are the Ratios of Elements, Compound, Mixture of its constituents?

A

Elements: -

Compounds: Fixed ratio

Mixtures: No fixed ratio

49
Q

What are Elements, Compound, Mixture’s properties like?

A

Elements: -

Compounds: Has different properties from its constituent elements

Mixtures: Usually has similar properties to its constituent substances

50
Q

Melting and Boiling Points of Elements, Compound, Mixture.

A

Elements: Fixed
Compound: Fixed
Mixture: Melt and boil over a range of temperatures.

51
Q

Isotopes have different chemical properties but may have different physical properties. TRUE/FALSE

A

FALSE.
Isotopes have similar chemical properties but may have different physical properties.

52
Q

What is covalent bonding?

A

A covalent bond is formed when non-metal atoms SHARE electrons to attain noble gas electronic configuration.

53
Q

(2) Covalent bonds can be formed between:

A

1- Atoms of the same element
2- Atoms of different elements (compounds).

54
Q

(2) Properties of Covalent substances (SIMPLE COVALENT MOLECULES)

A
  1. The atoms within simple covalent molecules are held together by strong covalent bonds.
  2. The simple covalent molecules are held together by weak intermolecular forces of attraction.
55
Q

Why do COVALENT SUBSTANCES have low melting point?

A

-They have weak intermolecular forces of attraction between molecules, hence it requires a small amount of energy to overcome the forces of attraction, resulting in low melting point.
-Larger molecules have higher melting and boiling points as the intermolecular forces of attraction become stronger when the molecule gets larger.

56
Q

(3) Physical properties of SIMPLE COVALENT MOLECULES

A
  1. Most simple covalent molecules are insoluble in water but soluble in organic solvents (oil, alcohol).
  2. Most covalent molecules are unable to conduct electricity due to the absence of mobile ions or electrons to carry charges.
  3. However, some covalent molecules can dissociate in water to form a solution that conducts electricity.
    (E.g: hydrogen chloride dissociates in water to form mobile H+ and Cl- ions.)
    dissociate- breakdown to form ions
57
Q

What are alloys?

A

A mixture of a metal with one or more other elements.

58
Q

(3) Why are alloys stronger and harder than pure metals?

A

-In a pure metal, atoms of the same size are packed regularly in layers.
Therefore, it is easier for layers of atoms to slide over one another when a force is applied.

-Pure metals are MALLEABLE (can be bent or flattened into a thin sheet) and DUCTILE (pulled into a wire wihtout breaking).

-However, in an alloy, the atoms of different sizes, which disrupt the orderly arrangement of atoms. This makes it more difficult for atoms to slide past one another when force is applied, making alloys harder and stronger than pure metal.

59
Q

(3) Physical properties of metals and alloys.

A
  1. High melting and boiling points
    Pure Metal- fixed
    Alloys- range
  2. Good conductors of HEAT
  3. Good electrical conductors
    (as there are valence electrons that are free to move throughout the strucutre.)
60
Q

Can:
-Ionic Compounds
-Covalent compounds
-Alloys & Metal
conduct electricity?
and why?

A

[Ionic compound]
-Can conduct electricity in AQUEOUS & MOLTEN state.
-> due to presence of mobile ions.

[Covalent compound]
-CANNOT conduct electricity in ANY state
-> due to absence of mobile ions & electrons.

[Alloy & Metal]
-Can conduct electricity
-> due to mobile electrons.

61
Q

What is the valency of an ion?

A

Its charge without the sign.

62
Q

What are transition metals?

A

Transition metals can form more than one stable ion and so they hae variable valences.

63
Q

(2) Exception of Valences from Roman Numerals

A

ZINC (Zn2+) and SILVER (Ag+), form only one common ion each.
-fixed valences

64
Q

Formula of Ammonium Ion.

A

NH4+ (valency: 1)

65
Q

Formula of Hydroxide Ion.

A

OH- (valency: 1)

66
Q

Formula of Nitrate Ion.

A

NO3- (valency: 1)

67
Q

Formula of Sulfate Ion.

A

SO4 2- (valency: 2)

68
Q

Formula of Carbonate Ion.

A

CO3 2- (valency: 2)

69
Q

What are spectator ions?

A

In chemical reactions, there are ions (such ions occur in both the left and right side of the equation)

70
Q

(3) Substacnes that do not ionise in solution

A

-Insoluble solids (metals, insoluble salts)
-Covalent liquids (water)
-Gases

71
Q

How are elements arranged in the Periodic Table?

A

Increasing Atomic number

72
Q

Across a period, elements in the same period have the same number of ____.

A

Electron shells

73
Q

Down a group, elements in the same group have the same number of ____.

A

Valence elctrons

74
Q

Why do Grp 17 elements have similar chemical property?

A

They have the same number of valence electrons , 7.

75
Q

What are metalloids?

A

Elements that have the properties of metals and non-metals.

76
Q

Across the period, there is a _______ in metallic properties and an _____ in non-metall properties.

A

decrease, increase
(from LEFT to RIGHT, elements change from metal to non-metal.)

77
Q

Down the group, there is a _______ in metallic properties and an _____ in non-metall properties.

A

increase, decrease

-SIZE of atom INCREASES down the group.
-outermost electron is FURTHER away from the attractive forces of nucleus.
-Electron(s) can be lot MORE easily.

78
Q

(5) Physical properties of GROUP 1 - Alkali Metals

A
  1. Soft & can be cut easily.
  2. Low melting points and boiling points
  3. Low densities - Li, Na and K float on water.
  • Down the group:
    4. melting points DECREASE (S -> L)
    5. Densities increase
79
Q

Test for hydrogen gas

A

Place a lighted splint as the mouth of the test tube. The lighted splint extinguish with a pop sound.

80
Q

(5) Chemical properties of Alkali Metals

A
  1. Alkali metals are extremely reactive.
  2. Alkali metals react with WATER to form ALKALI and HYDROGEN gas,
    [alkali metal + water -> alkali (soluble base) + hydrogen]
  3. Reactivity increase down the group as:
  4. SIZE of atom increases down the group
  5. and hence Valence Electron is lost more easily.
81
Q

Lithium’s Reaction With Water.

A

Lithium + water -> lithium hydroxide + hydrogen
-
[2Li (s) + 2H2O(l) -> 2LiOH (aq) + H2(g)]

82
Q

Sodium’s Reaction With Water.

A

[Sodium + Water -> Sodium Hydroxide + Hydrogen]
-
[2Na (s) + 2H2O (l) -> 2NaOH (aq) + H2 (g)]

83
Q

Potassium’s Reaction With Water.

A

Potassium + Water -> Potassium hydroxide + hydrogen
-
[2K(s) + 2H2O (l) -> 2KOH (aq) + H2 (g)]

84
Q

(5) Physical properties of Grp 17 - Halogens

A
  1. Non metals
  2. Exist as diatomic (2) molecules
  3. Low melting and boiling points
    Down the group:
  4. melting points increase
  5. colour intensities get DARKER.
85
Q

Appearance in R.T.P:
-Fluorine
-Chlorine
-Bromine
-Iodine

A

Flourine: pale-greenish gas
Chlorine: Yellow-greenish gas
Bromine: Red-brown liquid
Iodine: Purple-black solid
(Brown when dissolved in water)

86
Q

What is the boiling points and appearance of ASTATINE?

A

B.p: 337
Appearance: Black Solid

87
Q

What is displacement reaction?

A

A more reactive element that over (displaces) the less reactive element.

88
Q

(2) Chemical properties of Halogens

A
  1. When going down the group, the reactivity DECREASE.
  2. Halogens can undergo Displacement Reaction, a reaction in which one element takes the place of another element in the compound.
    -A more reactive halogen displaces a less reactive halogen from its HALIDE solution.
89
Q

What are halides?

A

Ion of Grp 17 elements

90
Q

(5) Physical properties of Grp 18 Noble Gases

A
  1. Monoatomic non-metals
  2. Colourless gases at room temperature
  3. Low melting and boiling points
  4. Insouble in water
  5. Unreactive
91
Q

What are the 2 reference elements in the Reactivity Series?

A

Carbon and Hydrogen

92
Q

What does Metal Displacement Reaction help us with?

A

Compare directly the reactivity of 2 metals.
(Help us place particular metals more precisely in the reactivity series)

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