chemical analysis Flashcards
(30 cards)
what is a pure substance?
a substance which contains only one type of compound or element e.g. pure water
give a property of pure substances
they melt and boil at specific temperatures
how do impure substances melt and boil?
impure substances melt and boil over a range of temperatures depending on how much of each substance is in the mixture
having impurities in substances will generally…
lower the melting point but increase the boiling point
what is a formulation?
a formulation is a mixture with a specific composition for a specific application/need
give 3 examples of formulations
-fuels
-medicines
-alloys
what is an element?
a substance made up of only type of atom
what is a mixture?
two or more different elements that are not chemically bonded
what is a compound?
a substance made up of two or more different types of elements that are chemically bonded
define chromatography
chromatography is a separation technique that separates mixtures with different rf values
give the first 3 steps for a paper chromatography method?
1-take a piece of filter paper and use a pencil to draw a line 3cm from the bottom of the sheet
2-add your substances of ink onto the pencil line using a pipette
3-fill a beaker with a shallow amount of water or ethanol, this is your solvent
give steps 4-5 for paper chromatogram method
4-place the filter paper into the solvent ensuring you do not submerge your pencil line and ink and secure the paper to a pencil using paper clips-rest on beaker (so it doesn’t fall)
5-place a lid on top to stop the solvent from evaporating
give steps 6-7 for the paper chromatogram method
6-allow the solvent to move through the paper, but remove the chromatogram before it reaches the top
7-allow the chromatogram to dry, then measure the distance travelled by each spot and by the solvent from the baseline
what is the stationary phase?
a substance or material that the molecules cannot move in-eg the paper
what is the mobile phase?
a substance that the molecules can move in-always a liquid or gas-eg the solvent
give the equation to calculate a rf value
distance substance moved/distance solvent moved
how do we test for chlorine?
to test for chlorine we insert damp litmus paper into the mouth of the test tube
what is the positive result for a chlorine test?
the chlorine will decolourise the litmus paper and turn it white
how do we test for hydrogen?
to test for hydrogen we remove the bung and insert a burning splint into the test tube “squeaky pop test”
what is the positive result for a hydrogen test?
hydrogen gas burns rapidly-produces a pop sound
how do we test for oxygen?
use a glowing splint and place into the test tube
what is the positive result for a oxygen test?
the splint will relight
how do we test for co2?
to test for co2 we use limewater-draw some of the gas into a pipette and bubble the gas through the limewater, and repeat
what is the positive result for a co2 test?
if co2 is present the limewater will turn cloudy
