Experimental techniques Flashcards
What apparatus is used to measure 25cm3 of acid very accurately? [1]
pipette, burette used to measure volume of liquid NEEDED
Describe the effect of heating a solution of lead(II) nitrate until it boils and then heating for a further ten minutes [2]
Evaporation
crystals formed
Some documents are stored in containers with packets of silica gel crystals. These crystals absorb water from air that enters the container. Water could damage the documents. Anhydrous cobalt(II) chloride is added to the silica gel. As the crystals absorb water they change colour from blue to pink. Heating the silica gel in an oven removes the water from the crystals so that the crystals can be reused.
Plan an experiment to find the mass of water absorbed by a packet of silica gel crystals [6]
mass of gel
heat in oven at 100
until change colour
reweigh
heat again to check constant mass
calculation
What does the term excess mean? [1]
more than enough to react
What should be used to transfer the copper from a bottle to the apparatus? [1]
spatula
Why was the apparatus left to cool before measuring the final volume of gas? [2]
return to initial temp
measure correct volume of gas
Why is gas bubbled through sulfuric acid [1]
remove impurities
Explain why crystals form [1]
solubility decreases as temp decreases
How could a student identify a simple sugar from its Rf value? [1]
compare with know substances
Sometimes not all the substances in a mixture can be identified from the chromatogram produced, explain why [1]
Similar Rf values
A hot water bath cannot be used to separate alcohols C and D, explain why [2]
water bath cannot exceed 100
c AND d have bp above 100
