Carboxylic acids and their derivatives Flashcards
When is redistillation used?
-When we want to purify volatile substances which can be purified further using separation.
How does the first part of separation work?
-Add the products from distillation into a separating funnel. Add water to dissolve soluble impurities and create an aqueous solution.
What is separation used for?
-Used to remove impurities that are dissolved in water.
What forms after the first part of separation when you allow the solution to settle?
-Top layer - impure product
-Bottom layer - aqueous layer containing soluble impurities. Drain the aqueous layer off. (Remember to remove the stopper).
What is the second step of separation?
-Purification
How does purification work?
Take the impure product from the separating funnel and ad it to the round bottomed flask
-Add anhydrous calcium chloride (CaCl2). This is a dehydrating agent and will remove any aqueous substances still remaining. INVERT the flask and leave for 20-30 minutes.
-Filter the solid drying agent to remove it.
How is filtration used?
-A vacuum is used
How to carry out this filtration.
-Place a filter paper disc in the Buchner funnel and dampen slightly to make a seal. Pour the reaction mixture into the Buchner funnel with the vacuum line on.
How does the vacuum work?
-The vacuum creates a reduced pressure in the flask and pulls the liquid through. The solid is left in the funnel.
What is recrystallisation?
-A method used to purify solids.
How does recrystallisation work?
-dissolve the product in minimum volume of hot water
-allow solution to cool and allow crystals to form
-filter off product using a Buchner funnel
How can you detect impurities?
-Measure the boiling point of the substance.
How is distillation used to measure impurities?
-Gently heat and measure the temp that the sample distils at.
-Compare this boiling point against the data book.
How do you know your sample contains impurities?
-your boiling point is higher than the one in the data book
-your sample boils over a range of temps.
How can the purity of a compound be measured?
-Measuring the melting point.
Method used to measure the melting point.
-Add a sample of the solid product into a capillary tube and place into the heating element of the melting point apparatus.
-Slowly increase the temp until the substance starts to melt.
-there is a temperature range from when the substance just starts to melt and when it fully melts.
-Compare the melting point against data book values.
Name two methods that can decrease the hydrolysis of fats.
-cooling
-removal of water
Why are antioxidants not regarded as catalysts?
-they are used up
-they react with free radicals
Why would a student prefer to use ethanoic anhydride instead ethanoyl chloride even though it has a slower rate of reaction?
-ethanoyl chloride reacts violently with H20 to produce HCL gas
during recrystallisation, why is the minimum quantity of hot water used?
-ensure the hot solution is saturated
during recrystallisation, why is the flask cooled to room temperature before the crystals were filtered off?
-yield is lower if warm
during recrystallisation, why were the crystals compressed in the funnel?
-air passes through the sample not just around it
a little cold water was poured through the crystals
-to wash away soluble impurities
