Chemistry OCR Gateway Revision

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  • Created by: charlotte
  • Created on: 12-06-13 15:04
the reaction between hydrogen and oxygen is..
exothermic
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describe a fuel cell
a cell supplied with fuel + oxygen and uses the energy from the reaction between them to create a potential difference
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word equation for the reaction in a fuel cell
hydrogen + oxygen ---> water
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balanced symbol equation for reaction in a fuel cell
2H2 + O2 ---> 2H20
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what changes take place at each electrode in a fue cell
electrode reactions and redox reaction
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why is the car industry developing fuel cells?
1. more laws being passed to reduce pollution from vehicles 2. cars powered by fuel cells are more efficient so less fuel is used
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adv of hydrogen/oxygen fuel
more efficient, direct energy transfer, less pollution
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word equation for iron rusting
iron + oxygen + water ---> hydrated iron (III) oxide
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what does a redox reaction involve?
reduction and oxidation (the loss and gain of electrons)
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why do oil, grease and paint prevent rusting?
they stop oxygen/water reaching the surface
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3 methods to prevent rusting
galvanising (zinc acts as barrier) sacrificial protection (use of metal e.g. magnesium which won't lose electrons) tinning (acts as barrier)
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OIL RIG
oxidation is loss (of electrons) reduction is gain (of electrons)
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what is an oxidising agent?
takes electrons off of a substance
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what is a reducing agent?
pushes electrons onto a substance
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word equation for fermentation
glucose ---> carbon dioxide + ethanol
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how is ethanol made by fermentation?
glucose + yeast solution, optimum temp for yeast, distillation occurs
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balanced symbol equation for fermentation
C6H1206 ---> 2CO2 + 2C2H5OH
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conditions needed for fermentation
absence of air, 25 degrees temp
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how is ethanol produced for industrial use? (hydration)
passing ethene and steam over heated phosphoric acid catalyst
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adv/dis of fermentation
renewable but large amounts of land needed
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adv/dis of hydration
cheaper but non renewable
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how is salt extracted as rock salt
underground cutting machines
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key features of electrolysis
hydrogen made at cathode, chlorine at anode, sodium hydroxide also made
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how have scientists' attitudes to CFC's changed?
they were first thought safe, but then found it decreased ozone layer so was banned
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what does action of ultraviolet light to do CFC's
leads to formation of chlorine atoms and therefore then depletion of the ozone layer
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what can CFC's be replaced by?
alkenes of HFC's (cfc's without chlorine)
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why do CFC's stay in stratosphere for a long time?
there is nothing to react with them
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temporary water hardness is caused by
dissolved calcium hydrocarbonate
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permanent water hardness is caused by
dissolved calcium sulfate
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equation to work out no. of moles
mass of chemical / molar mass
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describe electrolysis
the splitting up with electricity (a flow of charge & discharge ions)
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what happens to the ions in electrolysis?
positive move to cathode, negative to the anode.they are then discharged (turn into atoms or molecules)
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cm3 to dm3
1000cm3 = 1 dm3
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what do titrations find out?
the concentration of an alkali from the concentration of an acid (or vice versa)
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equation to find concentration
number of moles / volume (dm3)
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what is a limiting reactant
the reactant that is used up first
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equation for number of moles in a gas
volume of gas (dm3) / 24
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what happens when the position of equilibriam is on the right/left
right: concentration of product is greater than conc. of reactant. left: opposite
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factors that affect position of equilibriam
adding extra reactant, increasing pressure, increasing temp
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conditions needed in the contact process
V205 catalyst, 450 degrees temp, atmospheric pressure
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method of the contact process
sulfur dioxide burned in air, oxidisied to make trioxide, add water
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acid ionises in water to produce
H+
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strong acids..
completely ionise in water
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weak acids...
partially ionise in water
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ionisation of a weak acid is..
a reversible reaction
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ionic substances contain ions which are
in fixed positions but can move in the solution or when melted
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what must happen to ions for them to react
collide with other ions
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3 uses of sulphuric acid
preperation of metal surfaces, manufacture of fertilisers, car battery acid
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word equation for neutralisation
acid + base ---> salt + water
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what happens when an acid neutralises an alkali?
the hydrogen ions react with the hydroxide ions to make water
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ionic equation of neutralisation
H+ +OH- ---> H20
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equation for percentage yield
actual yield x 100 / predicted yield
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what do fertilisers do and how?
increase crop yield by replacing essential elements used by previous crop + provides extra. more nitrogen gets into plant protein so increased growth
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the haber process to make ammonia
nitrogen + hydrogen in an iron catalyst. high pressure, 450 degree temp
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factors that affect cost of making new substance
higher pressure, higher temp = higher cost. catalyst = lower cost
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balanced symbol equation for the haber process
N2 + 3H2 2NH3
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how does detergent work
hydrophillic head forms bonds with water + pulls grease off. hydrophobic tail forms bonds with oil or grease
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adv + dis of continuous manufacturing
adv: works at full capacity, makes large amounts of product. dis: costs a lot, only works with one level of output
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adv + dis of batch processes
adv: easy to change from making one product to next dis: not as efficient
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how are chemicals extracted from plant sources
crushing, dissolving suitable solvent, chromatography
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Card 2

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describe a fuel cell

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a cell supplied with fuel + oxygen and uses the energy from the reaction between them to create a potential difference

Card 3

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word equation for the reaction in a fuel cell

Back

Preview of the front of card 3

Card 4

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balanced symbol equation for reaction in a fuel cell

Back

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Card 5

Front

what changes take place at each electrode in a fue cell

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