chemical analysis Flashcards
how does impurities affect a sample
increases the range of temperatures, decrease accuracy MP, increase BP
will a substance move further if it is more attracted to the mobile or stationary phase?
mobile
how to calculate Rf value
distance travelled by the substance
how to test for hydrogen
Place a lit splint close to the mouth of a test tube that contains a gas.
If the gas is hydrogen, a “squeaky pop” sound will be produced.
This noise is generated because hydrogen burns rapidly in the presence of oxygen to give H2O.
how to test for oxygen
Insert a glowing splint into a test tube that contains a gas.
If the gas is oxygen, the splint will relight.
how to test for carbon dioxide
Take an aqueous solution of limewater (calcium hydroxide) and bubble through the gas.
If the gas is carbon dioxide, the limewater solution will turn from clear to cloudy.
how to test for chlorine
Insert damp bluelitmus paper into a test tube that contains a gas.
If the gas is chlorine, the litmus paper will change to red then bleach to white.
what flame does calcium have
orange-red
what flame does copper have
green
what flame does sodium have
yellow
what flame does lithium have
crimson
what flame does potassium have
lilac
what colour is magnesium hydroxide precipitate
white
what colour is aluminium hydroxide precipitate
white
what colour is calcium hydroxide precipitate
white
what colour is iron III hydroxide precipitate
brown
what colour is copper II hydroxide precipitate
blue
what colour is iron II hydroxide precipitate
green
test for carbonates method
bubbling the gas through limewater. If the solution turns cloudy, the gas is carbon dioxide and the compound is a carbonate.
test for halides method
Add dilute nitric acid to an unknown solution.
This removes carbonate ions. These could disrupt test results by forming a precipitate with the silver ions added in the second step.
Add silver nitrate to the same solution.
If halide ions are present, they will form a precipitate with the silver ions.
test for sulfates method
Add dilute hydrochloric acid to an unknown solution.
This removes carbonate ions. These could disrupt test results by forming a precipitate with the barium ions added in step 2.
Add barium chloride to the same solution.
If sulfates are present, the white precipitate barium sulfate will form
advantages of instrumental methods
Greater sensitivity and accuracy, Quicker at producing results, Able to analyse tiny samples.
disadvantages of instrumental methods
expensive, special training required
what ions does flame emission spectroscopy identify
metal, positive
