U2- Water Flashcards

1
Q

physical properties of water

A
  • polar compound made of discrete molecules
  • colourless, odourless liquid
  • freezes at 0C and boils at 100C
  • on earth, found in all three states of matter: solid, liquid and gas
  • less dense in solid phase than liquid phase
  • liquid water evaporates at all temperatures above 0C
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2
Q

why does water have polar covalent bonds

A

due to difference in electronegativity between O and H

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3
Q

what causes water to have poles (dipoles)

A

its bent shape

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4
Q

what is hydrogen bonding in water’s effect on its properties

A
  • high MP and BP vs other simple covalent substances
  • expansion of water upon freezing
  • high latent heat
  • high specific heat capacity
  • ability of water to dissolve other substances
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5
Q

why do we pick molecules of similar size for comparison of MP/BP?

A

Because the molecules have a similar exposed SA and number of electrons,
then they will have similar dispersion forces
[(therefore) assured that difference in MP/BP is only due to hydrogen bonds]

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6
Q

why does water have a high MP/BP?

A

Because each water molecule is capable of forming 4 hydrogen bonds, then these bonds require a lot of energy to disrupt/overcome

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7
Q

Compare BP of water vs ethanol (78C) and explain the difference

A

While both water and ethanol can form hydrogen bonds, dipole dipole forces and dispersion forces,
water forms more h bonds per molecule (4) than ethanol (2) which require more heat energy to disrupt
therefore water (100C) has a higher BP than ethanol (78C)

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8
Q

why does water expand will freezing?

A

as water cools, molecules slow down and adopt a more regular arrangement due to the rigid intermolecular h bonds
the resulting open, hexagonal crystalline lattice in the ice pushes molecules further apart then in liquid water, expanding the structure
therefore the sane number of molecules occupy a larger space and ice has lower density than water

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9
Q

Why does 1L block ice, when melting, produce roughly 900mL of liquid water?

A

As water heats up, the open, hexagonal crystalline lattice is disrupted, pushing molecules closer together allowing them to move more freely
therefore liquid water has a higher density than ice and the same amount of H2O will occupy a smaller volume

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10
Q

latent heat of fusion

A

energy required to convert 1 mol of a substance from a solid to a liquid at its MP
water = 6kJ/mol

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11
Q

latent heat of vaporisation

A

energy required to convert 1 mol of a substance from a liquid to a gas at its BP
water = 44kJ/mol

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12
Q

why is sweating on a hot day a good mechanism to cool warm bodies?

A

after sweat is produced it evaporates on skin
the energy required for this to occur (latent heat of vaporisation) is absorbed from the skin which therefore cools the skin.

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13
Q

Specific heat capacity (SHC)

A

the amount of energy required to raise the temp of 1g of substance by 1 degree Celsius
water = 4.18J/g/C

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14
Q

why does water have a high specific heat capacity?

A

Water has a relatively high SHC due to the extensive hydrogen bonding present. That is, the hydrogen bonds require lots of energy to break and so water can absorb a lot of heat before the temperature will begin to increase

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15
Q

why does water have high latent heat values?

A

because strong H bonds need to be disrupted at each change of state which requires a lot of energy

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16
Q

why do we add acid to water rather than water to acid?

A
  • when a large amount of energy is released into water, energy can spread easily through the liquid and can be absorbed due to high SHC without increasing the temperature by much
  • when a large amount of energy is released into acid, the energy causes a much higher temp increase potentially boiling the acid and releasing corrosive fumes as the acid cannot absorb/store the nrg as well
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17
Q

density

A

a measure of the mass of a substance per unit volume (eg g/L)

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18
Q

solution

A

an evenly distributed mixture of atoms, molecules or ions including liquid solvent and one more solutes

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19
Q

solvent

A

the primary component of a solution, in which one or more solutes are dissolved

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20
Q

solute

A

the atoms, ions or molecules which are dissolved in a solvent

21
Q

solubility

A

the maximum amount of a substance that can be dissolved in a given quantity of a solvent at a certain temperature (g/100g solvent)

22
Q

dissolution

A

the process of dissolving

23
Q

miscible

A

a description of 2 liquids which mix together readily

24
Q

immiscible

A

a description of 2 liquids which do not mix together readiliy

25
Q

solvation

A

the process of water molecules surrounding a solvent molecule or ion and bonding with it

26
Q

ionisation

A

a reaction between a molecule and water resulting in the formation of two dissolved ions

27
Q

suspension

A

where a solid substance is dispersed in a solvent but not dissolved. The solid particles are distinguishable from the solvent particles

28
Q

colloid

A

a stable suspension

29
Q

dissociation

A

the process of an ionic compound dissolving

30
Q

ion-dipole force

A

an attractive force between an ion and the oppositely charged pole of a polar molecule (eg water)

31
Q

precipitate

A

a solid formed when tow dissolved ionic compounds react to form an insoluble compound

32
Q

spectator ion

A

an ion present in solution when a reaction occurs but that does not participate in the reaction

33
Q

molarity

A

the number of moles of solute per L of solution

34
Q

ppm

A

parts per million: the concentration of a dissolved solute with the effective units of mg/L (in water) or ug/g

35
Q

%w/w

A

the concentration of a dissolved solute with the effective units of g/100g

36
Q

%w/v

A

the concentration of the dissolved solute with effective units of g/100mL

37
Q

%v/v

A

the concentration of dissolved liquid solute with the effective units if mL/100mL

38
Q

solubility curve

A

a graphical depiction of how the solute concentration required to form a saturated solution changes across a range of temperatures

39
Q

saturated solution

A

a solution in which the maximum amount of solute is dissolved at that temperature

40
Q

unsaturated solution

A

a solution in which less than the maximum amount of solute is dissolved at that temperature and in which more solute could dissolve

41
Q

supersaturated solution

A

a solution in which more than the maximum amount of solute is dissolved at that temperature. This is an unstable situation which can arise when a saturated solution cools, and is likely to result in crystallisation of some of the solute.

42
Q

crystallisation

A

where a dissolved solute forms a solid due to it being in a supersaturated solution, This often arises due to the cooling of a saturated solution; the slower the solution cools, the larger the crystals appear

43
Q

which ions are always soluble?

A
Sodium
Nitrate
Ammonium
Potassium
Ethanoates (CH3COO)
44
Q

soluble ions + exceptions

A

Na+, K+, NH4+, NO3-, CH3COO-
Cl-, Br-, I- except Ag+, Pb2+, Hg2+ ; PbCl2 is slightly soluble
SO4 -2. except Pb2+, Ba2+

45
Q

insoluble ions + exceptions

A

O2-, S2-, CO3 2-, PO4 3- except Li+, Na+, K+, NH4+

OH- except Na+, K+, NH4+, Ba2+, Ca2+

46
Q

what needs to happen for a substance to dissolve

A

forces being formed need to be approximately the same strength or stronger than the forces being broken

47
Q

how do polar covalent compounds ionise?

A

polar covalent bonds w/in the molecule new broken, producing hydrogen ions and anions
a covalent bond forms between the H+ and H2O molecule giving H3O+ ions
ion-dipole attractions are formed between the newly produced ions and the polar solvent (water) molecules

48
Q

homogenous vs heterogenous

A
homogenous= same state
heterogenous= different states