PAG style questions Flashcards
What are 2 limitations and their solutions when determining the formula of a hydrated salt by heating?
not all of the water may have been removed
solution: heat to a constant mass
metal salts can further decompose upon intense heating
solution: keep an eye on the colour of the salt and don’t over-heat
Name 4 sources of error when carrying out a determination of the enthalpy changes of combustion
evaporation of fuel from the wick
incomplete combustion of the fuel occurred
not under standard conditions
heat loss to surroundings
Name a piece of apparatus that could be used to improve an experiment to determine the enthalpy changes of combustion
bomb calorimeter
Why would you use hydrochloric acid in excess when determining enthalpy change by Hess’ law?
to make sure the reaction has been completed
How could you reduce heat loss to surroundings when when determining enthalpy change by Hess’ law?
add a lid and insulation
In the preparation of cyclohexene, how would knowing its density be useful during the purification process?
identification of the aqueous/organic layer
Why should phosphoric acid (V) be added slowly, rather than all at once as part of the preparation of cyclohexene?
prevents the temperature of the reaction increasing to unsafe levels and minimises the likelihood of formation of side-products
Describe how the final redistillation step allows a check to be made on the purity of the organic product in the preparation of cyclobenzene?
the closer to the boiling point and the smaller the range of the boiling point, the purer the product
distillates produced over range of temperatures surrounding the boiling point indicates the presence of impurities
When investigating the rate of reaction between magnesium and hydrochloric acid, one problem is that the reaction is exothermic. What effect will this have on the results? How could you reduce this problem?
a greater volume of hydrogen gas would be collected as heat released from the reaction would cause the hydrogen gas to expand
carry out the reaction using larger volumes so the heat energy is more spread out
