C8 Chemical analysis Flashcards
define pure scientifically
consists of only 1 element or compound
define alloy
a mixture of 2 or more elements (usually metals)
how many carats gold is 100% gold?
24
calculate the percentage of gold if the gild is 9 carat
37.5% gold
9/24 x 100
what makes a substance impure?
one different atom of molecule
give 3 examples of an alloy
steel, bronze, brass
what is steel made out of?
iron + carbon
what is steel bronze out of?
copper + iron
what is brass made out of?
copper + zinc
what is the main property of an impure substance?
the melting point is less then that of a pure substance
if a substance is impure, why is the melting point less than that of a pure substance?
because it often melts over a range of temperatures of the substances that its made up
how do you know the purity of a substance?
the greater the difference between tis known pure melting point, the lower the purity
what is a formulation?
a useful mixture with each substance having a precise purpose
how are formulations made?
by mixing the components in carefully measured quantities
what are 2 important stages of chromatography?
-the stationary phase
-the mobile phase
what are the 2 factors that the travel of a substance in chromatography depend upon?
-how soluble the substance is in the mobile
-the affinity to the stationary phase
if there is higher affinity in chromatography how does it affect the travel time?
the slower the substance moves in a set time
if there is more solubility in the substance for chromatography how does it affect the travel time?
it moves quicker in a set time
in the apparatus setup for chromatography why is there a lid on top?
prevents evaporation of solvent
in the apparatus setup for chromatography why is the line a pencil?
the pencil doesn’t dissolve in the solvent
in the apparatus setup for chromatography why is water used?
it dissolves colours and is absorbed through the paper
describe a method to work out a mixture of colours in the unknown sample is made up of
-use a ruler to draw a pencil line 2cm away from the edge of the paper
-put a small spot of known colourings and the unknown on the line equal distance apart
-label each spot in pencil
-pour water into the beaker but make sure the surface isnt toughing the colourings
-keep the paper vertical and ensure it doesn’t touch the beaker walls
-wait for the water to travel 3/4 up the paper
-remove the paper and wait for it to dry
-calculate the Rf values pf all the coloured spots
why do the ink spots in chromatography travel at different distances?
they have different solubilities/ affinities
how do you calculate Rf values?
distance moved by the substance / distance moved by the solvent
what will a pure compound show after a test of chromatography?
only one spot/ Rf value
what is the test for hydrogen?
-quarter fill a test tube w/ hydrochloric acid and add a small piece of magnesium
-block the end of the test tube to allow the gas to build up
-test the gas with a lighted splint
what is the test for oxygen?
-quarter fill a test tube with hydrogen peroxide and add a tiny bit of manganese dioxide powder
-block the end of the test tube to allow the gas to build up
-test the gas with a glowing splint
what is the test for carbon dioxide?
-half fill a test tube with limewater
-quarter fill a boiling tube with hydrochloric acid and add some marble chips
-put a bung with a delivery tube quickly into the boiling tube and the other end into the limewater
what is the test for chlorine?
-switch on the power supply to the electrolysis of sodium chloride
–wet a piece of litmus paper and hold it over the positive electrode
[if positive then it will blech the damp paper blue]
why must the level of solvent in the beaker be below the level of spots in chromatography?
the spots will dissolve in the solvent instead of moving up
what can flame tests NOT be used for?
to identify the metals present in a mixture of metal ions
what will the stronger colours do in a flame test?
block out the weaker colours
what is the line spectrum of a mixture of metal ions?
a combination of the line spectra of each individual metal ion present in the sample
what are the pros of chemical analysis?
-often simple to do
-cheap
what are the cons of chemical analysis?
-uses up the sample
-not quantitative
what are the pros of instrumental analysis?
-uses small samples (sensitive)
-fast
-accurate
what are the cons of instrumental analysis?
-machines can be expensive
what is the flame colour for lithium?
crimson
what is the flame colour for sodium?
yellow
what is the flame colour for potassium?
lilac
what is the flame colour for calcium?
orange-red
what is the flame colour for copper?
green
what are the Hydroxide precipitates test’s method?
Add a few drops of dilute sodium hydroxide solution. Observe and record the colour of any precipitate formed.
what precipitate does the positive metal ion aluminium turn (+does it dissolve)?
white - yes
what precipitate does the positive metal ion calcium turn (+does it dissolve)?
white - no
what precipitate does the positive metal ion magnesium turn (+does it dissolve)?
white - no
what precipitate does the positive metal ion copper turn?
blue
what precipitate does the positive metal ion iron (II) turn?
green
what precipitate does the positive metal ion iron (III) turn?
brown
what is the method for the Test for halide ions?
Add a few drops of dilute nitric acid, then a few drops of silver nitrate solution. Observe and record the colour of any precipitate formed.
what precipitate colour does chloride form?
white
what precipitate colour does bromide form?
cream
what precipitate colour does iodide form?
pale yellow
what is the test for sulphate ions and what do u see if there is a positive result?
Add a few drops of dilute hydrochloric acid, then a few drops of barium chloride solution. A white precipitate forms if sulphate ions are present.
Sulfate ions can be tested for using a dilute acid and which other solution?
barium chloride; Sulfate ions react with barium chloride to form a white precipitate.
Some unknown solutions were tested with silver nitrate solution in the presence of dilute nitric acid. The results are shown in the table. Solution 3 did not contain the expected type of ion but another negative ion that reacted with the acid. Name this negative ion.
carbonate ion; Carbonate ions react with the nitric acid to form carbon dioxide gas.
In flame emission spectroscopy, a sample is put into a flame and the light that is given out is passed through an instrument. What is the name of the instrument?
spectroscope
Complete the sentence. Carbon dioxide gas is produced when an __________ is added to a carbonate.
acid; Acids react with carbonates to form carbon dioxide gas
Instrumental methods of identifying ions are particularly useful when the amount of the sample is very __________. What is the missing word in this sentence? large or small
small; Instrumental methods are very sensitive, which means that they can detect very small amounts of a sample.
Name a carbonate that is soluble in water.
sodium; The group 1 carbonates are soluble in water, as is ammonium carbonate.
