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Year 11 Chemistry > Water > Flashcards

Water Flashcards

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1
Q

1.1

Define solute

A

the substance dissolved in a solution (can be a liquid or gas)

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2
Q

1.1

Define solvent

A

the liquid in the solution

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3
Q

1.1

Define solution

A

a mixture of a dissolved substance in a liquid. Solutions are ‘aqueous’ when the solvent in water

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4
Q

1.2

Identify the importance of water as a solvent

A

bloodstream: carries around digested food, oxygen, hormones and waste
cells: water is a solvent for oxygen and nutrients to be delivered to cells, and facilitates the transport of gases
transpiration stream: (movement of water from root to leaf in plants) Carries mineral nutrients for the plant to grow

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5
Q

1.3

What percentage of the hydrosphere is water? Give examples

A

95-99%

solid: polar ice, glaciers
liquid: oceans, seas, lakes, rivers

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6
Q

1.3

What percentage of the biosphere is water? Give examples

A

60-95%

liquid: cell protoplasm, transport systems (blood)
gas: water vapour in some organ spaces

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7
Q

1.3

What percentage of the lithosphere is water? Give examples

A

less than 10%

solid: frozen soil, hydrated minerals
liquid: aquifer, groudwater

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8
Q

1.3

What percentage of the atmosphere is water? Give examples

A
  1. 5-5%
    liquid: water droplets in clouds
    gas: water vapour
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9
Q

1.4

Why is water important in cells and in metabolism

A

Forms the basis for most life on earth - photosynthesis/respiration.
6CO2 + 6H20 +light energy -> 6C6H12O6 (aq) + 6O2

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10
Q

1.4

Why is water important in places with extreme temperature?

A

Water moderates temperature
It can absorb of release large quantities of heat energy with only small temperature changes
Temperatures near the coast are more moderated than inland areas

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11
Q

1.4

Why is water important in the weathering of rocks?

A

Assists with the formation of landforms and the production soil
Physical - weathering through constant motion or temperature
Chemical - water dissolving or reacting with minerals in rocks

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12
Q

1.6

Why are water and ice different densities?

A

Because as the temperature increases, so does the energy of the molecules in water. As energy decreases, the particles move closer together, and the material becomes denser

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13
Q

1.7

What is the effect of anti-freeze and salt on the boiling point of water? Why?

A

Adding both resulted in an increase in boiling point.

This is because a solution has more bonds than water alone, therefore requiring more energy to break

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14
Q

2.1

What is the VESPR theory?

A

Valence Shell Electron Pair Repulsion theory
The shape of molecules id determined considering electrostatic repulsion between valence shell electron paris. Atoms try to move as far apart as possible to decrease repulsion between negative particles

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15
Q

What is a pure covalent bond?

A

Between two of the same atoms. The electrons are attracted evenly to each nucleus, therefore the molecule is even

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16
Q

What is a polar covalent bond?

A

One nuclei has a slightly stronger attraction to the shared electrons.
This occurs between non-metal atoms of different electrons, and depends on electronegativity.

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17
Q

When is a molecule with polar bonds non-polar?

A

When each bond polarity cancels another out. The molecule has a vector sum of zero

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18
Q

What determines the state of a compound?

A

Its intermolecular attractions

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19
Q

What is a dispersion force?

A

The weakest intermolecular force, found in non-polar molecules.

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20
Q

What is dipole-dipole bonding?

A

Found in polar molecules, second weakest bond

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21
Q

What is hydrogen bonding?

A

Dipole-dipole bonding between hydrogen and either oxygen, fluorine or nitrogen.

22
Q

2.5

Explain surface tension of water in terms of intermolecular forces

A

Molecules at the surface of a liquid have forces directed towards the bulk of the material, creating tension. Water’s surface tension is high because of hydrogen bonding

23
Q

2.5

Explain viscosity of water in terms of intermolecular forces

A

Viscosity is the resistance of fluid to flow.

The molecules of water are relatively small, therefore water is viscous.

24
Q

2.5

Explain melting and boiling points of water in terms of intermolecular forces

A

Hydrogen bonding in water means that it has a high melting and boiling point than other molecules of its size e.g. ammonia

25
Q

3.1

Explain the changes when soluble ionic compounds react with water

A
  • Breaks into ions
  • Most ionic compounds dissolve in water because of the attraction between the polar ends of H2O and the charged ions.
  • FORMS ION DIPOLE FORCES (between dipole and hydrogen in strength)
  • Dissolves if the forces between ions and charged ends of water are stronger than original ionic bond
  • Called DISSOCIATION REACTION
  • e.g Sodium chloride
26
Q

3.1

What are the two types of molecular compounds that react with water?

A
  1. Ones that form hydrogen bonds
    - Polar substances e.g. glucose, ethanol
  2. Ones that react with water
    - e.g. hydrogen chloride - negative end is attracted to strongly to water that the molecule breaks, forming a new substance - Hydrochloric acid
27
Q

3.1

Explain the changed when partially soluble molecular elements are mixed with water

A

e.g. iodine, oxygen - weak dispersion interactions between water and the element

28
Q

3.1

What type of substances are insoluble in water?

A
  • large molecules e.g. cellulose - too many strong covalent bonds to be broken by H2O.
  • covalent network substances e.g. diamond - too may strong bonds
29
Q

3.2

What is the relationship between the solubility of substances in water and the polar nature of the water molecule?

A

‘like dissolves like’ - generalisation
Polar molecules dissolve in polar substances because of the attraction between the slightly positive/negative ends of the molecules.

30
Q

4.1

When does a precipitate form?

A

When the ions of two solutions swap partners, and one of the new substances is insoluble, it will form a precipitate

31
Q

4.1

What is spectator ion?

A

The ions in a precipitation reaction which do not combine to create the precipitate, therefore do not go through any chemical changes

32
Q

4.2

Describe what happens to the movement of ions when solution and precipitation occur

A
  • The electrostatic forces in the original ionic compound break and the crystal dissolves
  • Intermolecular forces between some water molecules must be overcome to break and bond with ions (to form solution)
  • A precipitate will form if the attractive forces of the ions of the two solutions are stronger than the bonds between the ion and the water molecule.
33
Q

4.3

Identify the dynamic nature of ion movement in a saturated dissolution

A

Saturated solution = where no more solute can dissolved in a fixed volume at a fixed temperature

  • Rate of dissolving = rate of crystallising
  • Some molecules dissolve at the same time as other crystallise -> DYNAMIC
34
Q

4.4

What is molarity of a solution?

A

The number of moves per litre
c=n/V
(c=molarity, n=moles, V=volume in L)
[Na+] means concentration of Na+, in mol/L)

35
Q

4.5

What is percentage composition and why is it used?

A

% - parts per 100

- general applications, shopping, food industry, pharmaceutical

36
Q

4.5

What is parts per million and why is it used?

A

mg/kg

used to identify and show trace elements e.g. forensic reports, pollution monitoring

37
Q

4.5

What is molarity and why is it used?

A

moles per litre

easy for chemist to relate to quantities on a macro level, and write reaction equations on a symbolic level

38
Q

4.5

What is ‘grams in a volume’ and why is it used?

A

grams (of a solid) per litre of a solution

general commercial labelling for solid solutes

39
Q

5.1

What is specific heat capacity?

A

symbol ‘c’
It is the amount of heat needed to raise the temperature of 1.00g of a substance by 1ºC
units = J/kJ/mol

40
Q

5.2

Why does water have a high heat capacity?

A

When hydrogen bonds break, high amounts of energy is absorbed, and when they break, large amounts of energy are released.

41
Q

5.2

What are the specific heat capacities of some other solvents?

A 
Ethanol: 2.44 x10^3
Ethylene glycol (anti-freeze): 2.39x10^3
Carbon tetrachloride: 0.681x10^3
Steel: 0.47x10^3
Mercury: 0.14x10^3
42
Q

5.3

What does the equation ∆H=-mc∆T mean?

A

It calculates enthalpy, which is the measure of the change in heat content of a substance.
The heat content is potential energy, so cannot be measured. This equation measure the change in heat content.

43
Q

5.3

How do you measure the change in enthalpy of a solution?

A

∆H / moles of a solute

44
Q

5.4

How is water’s ability to absorb heat used to measure energy changed in chemical reactions?

A

CALORIMETR - the measure of heat changes in a system
Heat is released or absorbed in a chemical reaction and then absorbed or released by the water.
A calorimeter measure the resulting change in temperate

45
Q

5.5

Explain an endothermic reaction

A 
GETS COLD
energy is absorbed from the surroundings
heat content of the system increases
heat content of the surroundings decreases (measured)
∆H positive
e.g. solution of NaCl
46
Q

5.6

Explain an exothermic reaction

A 
GETS WARM
energy is related into the surroundings
heat content of the system decreases
heat content of the surroundings increases (measured)
∆H negative
e.g. solution of NaOH
47
Q

5.6

when is energy absorbed?

A

To separate particles

48
Q

5.6

When is energy released?

A

To form bonds between particles

49
Q

5.7

Why is water’s ability to absorb heat important to aquatic organisms and life on earth?

A

Aquatic life: Keeps environment at a constant temperature

Other life: regulates earth’s temperature by absorbing extreme temperatures. Acts as a regulating agent in the body

50
Q

5.8

What is thermal pollution?

A

The discharge of large quantities of hot water into rivers and lakes significant enough to increase the body’s temperature by 2-5ºC

51
Q

5.8

What are the issues surrounding thermal pollution

A

Solubility of oxygen decreases as water temperature increases -> harms aquatic life
Fish eggs to not hatch and develop if temperatures are too high
Sudden temperature changes can kill fish or eggs, even if the temperature is in the organism’s survival range

Year 11 Chemistry (3 decks)

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