chapter 1 Flashcards
separation techniques, subs.
what is crystallisation
→ obtain pure solid from saturated solution
steps for crystallisation
step 1: impure solid dissolved in solvent
step 2: solution is heated to obtain hot saturated solution (no more solute can be dissolved)
step 3. hot saturated solution is allowed to cool, dissolved solid appears as pure crystals
what is simple distillation
→ separates a pure liquid from solution (diff boiling points)
what is important in setting up the apparatus in simple distillation
** bulb of thermometer should be at the entrance of condenser → measures boiling point of subs
** water in is below water out in condenser
what does boiling chips do
ensure smooth boiling
why are conical flasks usually used to collect distillate
it has a smaller surface area → slower rate of evaporation
how do you dry gases
use drying agents → absorbs moisture
how do you dry ammonia
using calcium oxide (solid)
how do you dry acidic gases
using concentrated sulfuric acid (liquid) and FUSED calcium chloride (solid)
can you use concentrated sulfuric acid to dry ammonia
no they will react with each other because they are acidic and alkaline
what are the acidic gases
chlorine, hydrochloric gas, nitrogen dioxide, carbon dioxide, sulfur dioxide
what are the neutral gases
carbon monoxide, hydrogen, argon, oxygen, helium, nitrogen monoxide
what is the only alkaline gas
ammonia
properties of pure substances
- melts and boils at fixed temp
- only have one spot on chromatogram
what does chromatography do
→ separates a mixture of substances which have diff solubilty in a solvent
steps for chromatography
step 1: draw the starting line in pencil and place a small spot of the sample on the line
step 2: dip the paper into the solvent, make sure solvent is below the start line
step 3: diff. solutes are soluble to the diff. extent in the solvent and a chromatogram forms (when solvent moves up paper)
step 4: draw the solvent front in pencil when solvent is near the top of the paper
why is the starting line drawn in pencil
→pencil lead is made up of carbon which doesn’t dissolve in the solvent and not move up the chromatogram. (dosen’t interfere with chromatogram)
why must the solvent be below the starting line
→ to ensure that chromatogram to be separated do not dissolve in the solvent (otherwise, no chromatogram will be developed)
why must the spot of the sample at the start line be small
→to ensure that the spots don’t smudge and overlap as this will make identification of the components in the sample difficult
why should the chromatogram be as long as possible
→ to ensure a better chromatogram of the components
why do we need to cover the beaker with a lid during chromatography
→ to slow down evaporation of the solvent and to maintain a saturated vapor mixture within the beaker
how to identify colourless substances
→ locating agents are used to make colourless substances on chromatogram more visible
what is Rf value
→ dist. travelled by solute / dist. travelled by solvent
→ accuracy: 2 d.p. (no units)
→ higher Rf value, higher solubility (subst. travelled further)
what is fractional distillation and their industrial uses
→ to separate miscible liquids w close boiling points
→ industrial use: crude oil, liquid air, fermented alcohol
