as chemistry amount of substance

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as chemistry amount of substance
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2013-10-27 11:31:46
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  1. a base is a substance that has
    a pH greater than 7
  2. an alkali is a
    • base that dissolves in water 
    • it forms OH- ions in water
  3. acid + metal oxide
    salt + water
  4. acid + metal hydroxide
    salt + water
  5. acid + metal carbonate
    salt + carbon dioxide + water
  6. acid + metal
    salt + hydrogen
  7. acid + metal hydrogen carbonate
    salt + carbon dioxide + water
  8. acid + metal sulphite
    salt + sulphur dioxide + water
  9. a fully balanced equation or stoichiometric equation is one that shows
    the formulae of reactants and products and the relative number of particles reacting
  10. find the compound formula of Al^3+ and S2O3^2-
    • Al2(S2O3)3 
    • notice how the charges have been switched round
  11. an ionic equation is one where
    the ions are represented separately
  12. only ..... compounds can be represented as ions . ............................................................................................................................................................................
    • ionic 
    • covalent substances and elements cannot be represented as ions . Also ionic solids cannot be represented as free ions because they are not free to move
  13. how to form a ionic equation
    • split all the ionic compounds into their free ions where possible 
    • cancel spectator ions in the equation (if the same ion appears in the reactants and products the ions cancel)
  14. percentage of an element =
    • Ar of an element x number of atoms of       that element in the compound 
    • ----------------------------------------------- x100
    • Mr of compound
  15. how many particles does a mole contain
    6.023 x 10^23
  16. what is the definition of the avogadro constant or avogadro number
    • the number of atoms in 12g of carbon12
    • avogadro constant - the total number of particles in a mole of substance also called the avogadro number it is numerically equal to 6.023 x 10^23
  17. mole
    a quantity of a substance that contains the avogadro number of particles (e.g. atoms , molecules , ions)
  18. :)
    :)
  19. one mole of entity has a mass in grams equal to its Ar or Mr and contains 6.023 x 10^23 . this mass is known as
    molar mass
  20. how to calculate the number of atoms in an entity
    • 1) Ar or Mr
    • 2) number of moles (mass/Mr or Ar) 
    • 3) number of moles x avogadros constant (we get number of molecules which is equal to molar mass)  
    • 4) number of molecules x number of atoms
  21. one atom of hydrogen 1 weighs 1.673 x 10^-24 what's the molar mass
    • stage 2 
    • number of moles = mass/mr 
    • number of moles = 1.673 x 10^-24/1 
    • number of moles = 1.673 x 10^-24 
    • stage 3
    • 1.673 x 10^-24 x 6.023 x 10^23 = 0.986 g (3sf)
  22. how many atoms of carbon are there in 1 mole of bunchy balls . each ball has 60 atoms
    • stage 3 
    • number of moles x avogadros constant 
    • 1 x 6.023 x 10^23 = 6.023 x 10^23
    • stage 4 
    • molecules x number of atoms 
    • 6.023 x 10^23 x 60 = 3.61 g (3sf)
  23. calculate the number of nitrate ions in 20g of alumiunium nitrate
    • determine formula 
    • Al(NO3)3.9H2O
    • stage 1 
    • Mr = 27+ (14 x 3) +(16 x 9) + 9((2 x 1) + 16) = 375
    • stage 2 
    • number of moles = mass/mr 
    • number of moles = 20/375 
    • stage 3 
    • number of moles x avogadros number = number of molecules 
    • 20/375 x 6.023 x 10^23 
    • stage 4 
    • number of molecules x number of nitarte ions
    • 20/375 x 6.023 x 10^23 x 3 = 9.64 x 10^24 (3sf)
  24. how to calculate the number of ions in an entity
    • 1) Ar or Mr
    • 2) number of moles (mass/Mr or Ar) 
    • 3) number of moles x avogadros constant (we get number of molecules)
    • 4) number of molecules x number of ions
  25. molar mass in g
    (will just be asked the mass of one mole of ......)
    Ar or Mr x avogadros constant
  26. an accurate value for the mass of one mole of hydrogen atoms is 1.0080 g give a reason why this value is different from your calculated answer
    the accurate value may be an average value calculated using values of data from all isotopes
  27. molar mass in g/mole
    Mr or Ar
  28. number of moles
    mass/mr
  29. relationship between volume occupied by a gas and temperature
    • note temperature should be measured in kelvins 
    • V is proportional to T as long as the pressure remains constant 
    • V/T = constanT 
    • this is Charles law
  30. relationship between volume occupied by a gas and pressure
    • the product of pressure and volume is constant as long as the temperature remains constant 
    • PV = constant 
    • this is Boyles law
  31. the volume law - Gay Lussac's law
    • the pressure is proportional to the temperature as long as the volume remains constant 
    • P/T = constant 
    • combining all the realtionships gives us the equation : PV/T = constant for a fixed volume of gas
  32. what also affects the volume that we haven't mentioned yet
    • moles 
    • volume is proportional to the number of moles providing the temperature and pressure is constant
    • V/n = constant
  33. combining equations again
    • PV/Tn = constant 
    • since we have taken one mole of gas , the constant is given the R symbol and is called the gas constant . for N moles of gas we have : PV=nRT
    • the value of R is 8.31Jk^-1mol^-1 this is given in exams 
    • this equation is called the ideal gas equation
  34. when using the ideal gas equation , consistent units must be used . If you want to calculate n , the number of moles :
    • P must be in Pa (Nm^-2)
    • V must be in m^3
    • T must be in K 
    • R must be in JK^-1mol^-1
  35. rearranging the ideal gas equation for volume
    V = nRT/P
  36. rearranging the ideal gas equation for pressure
    P = nRT/V
  37. rearranging the ideal gas equation for number of moles
    n = PV/RT
  38. rearranging the ideal gas equation for temperature
    T = PV/nR
  39. :)
    :)
  40. compound x is a volatile liquid . in order to determine the relative molecular mass of X , a student carried out 6 experiments . In each experiment a measured mass of X was injected into an empty 100cm^3 gas syringe maintained at a pressure of 100kPa and a temperature of 373K . in each of the experiments the volume of gas produced was measured . 
    apart from the loss of liquid during transfer to the gas syringe , identify one other source of error in this experiment . suggest one improvement to minimise this other source of error
    • source of error = the temperature may not have constantly remained at 373K 
    • improvement = the experiment should be done in a water bath where the temperature is constant

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