The Oceans

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  • Created by: Sabina
  • Created on: 07-04-16 19:51
How does water form hydrogen bonds?
Water molecule are polar it has a partially negative oxygen and a partially positive hydrogen.The hydrogen in one water molecule is attracted to the lone pair on the oxygen of another molecule
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What are the unusual properties of water?
Has high boiling point, specific heat capacity and enthalpy of vapourisation and also is more dense than ice
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Why does water have a high boiling point?
In order to boil a liquid you need to overcome its intermolecular forces. As water forms hydrogen bonds which are strong a larger amount of energy is required in order to break its intermolecular bonds
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What is enthalpy of vapourisation?
Amount of energy needed to change a substance from its standard state to a vapour
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Why does water have a high enthalpy of vapourisation?
Water needs a lot more energy to evaporate than most other liquids
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What usually happens to the density of a substance as temperature decreases?
Density increases
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Why is water more dense than ice?
As water freezes, all the hydrogen bonds that are able to form, form. This causes it to form a lattice structure with lots of space making it less dense
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What happens to the density as ice melts?
Some hydrogen bonds break and the lattice breaks down, allowing water molecules to 'fill in' the gaps, increasing the density
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What happens when a solute dissolves?
Bonds within the solvent and solute break and new bonds are formed between the solute and solvent
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When will a solute not dissolve?
If the bonds to be broken are stronger than the bonds that will be formed
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Why will ionic substances not dissolve in non-polar solvents?
Non-polar molecules don't interact strongly enough with ions to full them away from the ionic lattice. The electrostatic forces between the ions are much stronger than any of the bonds that could be formed between the ions and the solvent molecules
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Why do most covalent substances only dissolve in non-polar solvents?
Covalent bonds are weak.They can be broken by non-polar solvents
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What are the two main types of solvent?
Polar (e.g. water) and non-polar (e.g. hexane)
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Why are ionic compounds able to dissolve in polar solvents?
The partially positive charge attracted to - ions, whilst the partially negative is attracted to + ions.Ions separated from ionic lattice surrounded by polar solvent.Total attraction from polar solvent can overcome strong ionic attraction in lattice.
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What is hydration?
When ions are surrounded by water molecules when dissolving
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What is solvation?
When ions are surrounded by a solvent when dissolving
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What is standard lattice enthalpy?
The enthalpy change when 1 mole of a solid ionic compound is formed from its gaseous ions under standard conditions
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Why is lattice enthalpy always negative?
Because it is an exothermic reaction
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What happens when an ionic lattice dissolves in water?
Bonds between the ions break this is endothermic (this is endothermic). Bonds then form between the ions and water (exothermic) this is done by hydration this is enthalpy of hydration
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What is enthalpy of hydration?
The enthalpy change when 1 mole of aqueous ions is formed from gaseous ions
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What is the overall effect on the enthalpy when a substance dissolves?
The enthalpy change of solution-it is the net effect of lattice enthalpy and enthalpy change of hydration
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What is enthalpy change of solution?
The enthalpy change when 1 mole of solute is dissolved in sufficient solvent that no further enthalpy change occurs on further dilution
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What is first ionisation enthalpy?
The enthalpy change when 1 electron is removed from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions
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What is second ionisation enthalpy?
The enthalpy change when 1 electron is removed from each ion in 1 mole of gaseous 1+ ions to form 1 mole of gaseous 2+ ions
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What are the three main factors that affect the size of the ionisation enthalpy?
Atomic radius-less attraction to nucleus if greater radius, nuclear charge-more protons in nucleus more attraction to outer electrons and electron shielding-inner electron shells shield outer electrons from attractive force of nucleus
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What happens to the first ionisation enthalpy down a group and why?
Decreases as the atomic radius increases and more electron shells so more shielding from inner shells
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What happens to the first ionisation enthalpy across a period? Why?
Increases as the number of protons is increasing so there is stronger nuclear attraction. Also they mostly are at the same energy level and so there is little change in atomic radius or electron shielding
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What factors affect entropy?
The physical state, the amount of energy a substance has and the number of particles
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How does the amount of energy that a substance has affect entropy?
The more energy quanta a substance has the more ways they can be arranged and so the greater the entropy
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What is quanta?
Fixed packages of energy
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How is total entropy change calculated?
total=system+surroundings
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How is entropy change of the system calculated?
system=products-reactants (difference in entropy between the reactants and products)
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How is entropy change of the surrounding calculated?
surrounding= -enthalpy change/T
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What are the units of entropy?
JK^-1mol^-1
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What is needed in order for a reaction to be spontaneous or feasible?
The total entropy change must be positive. If the entropy change in the system is negative there must be a positive change in the surrounding for the reaction to still be spontaneous
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What is an acid?
A proton donor- release H+ when mixed with water. H+ is never alone in water, it is combined with water to form hydroxonium ions H30+
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What is a base?
Proton acceptor-When in solution they take hydrogen ions from water molecules
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What happens to strong acids and bases in water?
Ionise almost completely in water -nearly all H+ released and accepted
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What happens to weak acids and bases in water?
Ionise only slightly in water- only a few H+ released and accepted
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Where does equilibrium lie for weak acids and for strong acids?
Equilibrium is far to the left for weak acids and far right for strong acids
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What do acids and bases form?
Conjugated pairs
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What can act as an acid and a base?
water
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How is ionic product of water calculated?
Kw=(H+)(OH-)
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What will cause a change in the ionic product of water?
temperature
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What are the units for Kw?
mol2dm-6
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What is a neutral solution?
A solution where the concentration of H+ is equal to the concentration of OH-
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What is the pH scale?
Measure of the concentration of H+
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How is pH calculated?
pH= -log10(H+)
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What is a monoprotic acid?
Acids that are able to donate one proton per molecule during dissociation
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How is concentration of H+ calculated if pH is given?
Inverse log10 of -pH --> 10^-pH
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How is the pH of a base calculated?
(H+)=Kw/(OH-)
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How is the pH of a weak acid calculated?
Ka=(H+)2/(HA)
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How is pKa calculated?
-log10(Ka)
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How do you calculate Ka from pKA?
10^-pKa
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What is a buffer?
A solution that resists changes in pH when small amounts of acid or alkali are added
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What are the two different types of buffers?
Acidic buffers and alkaline buffers
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How is an acidic buffer made?
By mixing a weak acid with one of its salts
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Give an example of an acidic buffer
Ethanoic acid and sodium ethanoate
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What is produced when ethanoic acid dissociated?
CH3COOH H+ + CH3COO-
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What ensures that the acidic buffer ethanoic acid can cope with the addition of acid?
The large number of CH3COO- ions which combine with the H+ to form CH3COOH. This shift the equilibrium to the left reducing the H+ concentration
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Name some of the things that contain buffers
Shampoos, cells and blood
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Explain how cells use buffers
Need a constant pH to allow the biochemical reactions to take place. pH is controlled by the buffer based equilibrium between dihydrogen phosphate ions and hydrogen phosphate ions
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Explain how blood uses buffers
Buffered using carbonic acid. The levels of H2CO3 are controlled by respiration
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State the assumptions that can be made when calculating the pH of a buffer
1. Ion is fully dissociated so assume the equilibrium conc, of the dissociated ion is the same as the initial conc, of undissociated ion 2.Slightly dissociated so conc, is same as initial conc.
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What is the advantage of CO2 dissolving in the oceans?
Helps slow down global warming
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What are the disadvantages of CO2 dissolving in the oceans?
When CO2 dissolves it causes the ocean to become slightly acidic this change in pH can cause harm to many species and damage the ecosystem. Other species that are not harmed by the pH can be affected as the food chain is disturbed
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What is the equation for CO2 dissolving in water?
CO2+H20 H+ +HCO3-
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How can the levels of CO2 released be reduced?
Use less fuel and using different fuels
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How does using less fuel reduce the amount of CO2 released?
Increasing the efficiency of devises e.g. engines means less energy is needed, so less fuel is burned and less CO2 is released
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How does using different fuels reduce the amount of CO2 released?
CO2 is released when fossil fuels, oil, coal and gas are burned. So different fuels can be used which produce less CO2, such as nuclear energy and hydrogen
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What are the disadvantages of using nuclear energy?
1.Helath risk concerns 2.Risks of accidental leaks or major disasters 3.Waste product remains radioactive for hundreds of years so must be stored safely and permanently 4.CO2 produced during mining and transportation on nuclear fuel
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What are the disadvantages of using hydrogen energy?
1.Hard to store and transport 2.Although only by product is water energy is required to produce it. This energy comes from fossil fuels which release CO2
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How can CO2 be removed from the atmosphere?
Photosynthesis and carbon capture and storge (CCS)
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How does photosynthesis remove CO2 from the atmosphere?
Reforestation means that there would be more trees to take in CO2 for photosynthesis
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How does carbon capture and storage remove CO2 from the atmosphere?
CO2 is captured as it is produced and piped into porous rock under the sea to be stored
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What are the unusual properties of water?

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Card 4

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