physical chemistry y2 Flashcards
What important factor needs to be considered when deciding on the most suitable indicator to use for a titration?
-vertical section on pH curve matches pH of indicator
how can a buffer be prepared from ammonia and glycolic acid (HOCH2COOH)
-ammonia reacted with excess glycolic acid
NH3 + HOCH2COOH —> HOCH2COONH4
Kw increases as temperature increases, does this suggest that dissociation is endo or exothermic
endothermic
Many experimental measurements use published data, such as Kw, measured at 25°C. Often these measurements have been taken at different temperatures, especially in experimental work carried out at body temperature.
What is the consequence of this for published scientific work?
inaccurate/invalid
Plan an experiment that a student could carry out to measure the enthalpy change of neutralisation
- acid and alkali needed
- 25cm^3 each
- temp taken at start and finish
- Q=mc delta T
- divide by number of moles
- enthalpy of neut= -energy change
When dissolved in water, the enthalpy change of solution of the salt potassium fluoride, KF, is –15 kJ mol–1.
The salt rubidium fluoride, RbF, has an enthalpy change of solution in water of –24 kJ mol–1.
Suggest reasons for the difference between the enthalpy changes of solution of KF and RbF
- K+ has smaller radius
- lattice enthalpy of KF is more negative than RbF / K+ has greater attraction to F-
- enthalpy change of hydration of K+ is more negative than Rb+
- enthalpy change of solution is affected more by lattice enthalpy than hydration enthalpy
why is second electron affinity of oxygen positive
O- ion and electron are both negative so energy is required to break bond
lattice enthalpy definition
enthalpy compound when 1 mol of a solid compound forms from its constituent gaseous ions
why is ionisation energy endothermic
energy needed to overcome force of attraction between outer electrons and nucleus
why is first electron affinity exothermic
involves electron experiencing attraction to nucleus
why is second ionisation energy more exothermic
- electron lost is closer to nucleus
- electron lost from particle which is already positive
- one more proton than electron
- outer electron more firmly attracted to nucleus
standard electrode potential
emf of half cell compared with a hydrogen half cell, 298k, 100kPa, 1 moldm-3
Give two reasons why it is uncertain whether reactions predicted from electrode potential values may actually take place
- high activation energy
- conditions not standard
cell equilibrium, does oxidation/reduction shift right or left
oxidation (more negative) shifts left
positive right
Suggest two advantages of using methanoic acid as the fuel in a fuel cell rather than hydrogen
- liquid easier to store
- gives greater cell potential
