C12 Flashcards
define solute
a substance which dissolves
what is a solvent
the substance which does the dissolving
what is a solution
a substance with a mix of the solvent and solute
what is paper chromatography
a method to separate mixtures of colour compounds
what are some examples of substances which are suitable for paper chromatography
inks, dyes and food colourings
what is the base line
the line at which the inks are placed on
what is the mobile phase
it is the solvent chosen which moves up through the chromatography paper
what is the stationary phase
the chromatography paper
If a substance has a stronger force of attraction to the mobile phase, what happens
the compound will travel a greater distance in a given time
If a substance has a stronger force of attraction to the stationary phase, what happens
the compound will not travel far in the same time
what is Rf value
the retention factor
what is Rf value used for
it is used for comparing the components of various samples
what is the solvent front
the point at which the solvent stopped moving up the paper
what is the solvent front also known as
the solvent height
how do you calculate the Rf value
distance from base line to the centre of the ink spot divided by distance from base line to the solvent front
if two substance have the same Rf value, what does that mean
this means they are likely to be the same compound. this is not 100% guaranteed though.
if two substances do not have the same Rf value, what does that mean
they are 100% not the same compound
can a Rf value be over 1
NO, NOT EVER WILL THE Rf VALUE BE OVER 1
how many types of substances are there
there are 2 main types of substances: mixtures and pure substances
what is a pure substance
a substance where all the particles are the same
what is a mixture
a substance with different types of particles which are not chemically bonded together
how do you test if a substance is pure or not
you need to check if the melting or boiling point of a substance is exact.
what is the difference in melting or boiling points of a pure substance and a mixture
a pure substance melts at exact points while mixtures boil/melt at a range of temperatures
what is a formulation
a mixture which has been designed to produce a useful product
what does impurities do in a pure substance
they tend to lower the melting point and increase the boiling point
what are 3 examples of formulations
alloys, fertilisers and medicines
what is the test to test for hydrogen gas. list the steps
squeaky pop test
1. in a boiling tube add 3cm cubed of hydrochloric acid
2. add a piece of magnesium ribbon into the boiling tube an quickly cover the tube with a bung
3. 20 seconds later get a burning splint and remove the bung and instantly hold it at the mouth of the tube
4. the lighted splint should pop
what is the test for carbon dioxide gas. list the steps
lime water turns cloudy
1. add 3cm cubed of lime water to a boiling tube
2. get another boiling tube which has a delivery tube attached and add 4cm cubed of hydrochloric acid
3. add a spatulas worth of sodium carbonate into the boiling tube with hydrochloric acid.
4. cover the top with a bung attached to a delivery tube and pass the gas into the limewater in the boiling tube.
5. the lime water should turn cloudy
what is the test for oxygen gas. list the steps
glowing splint re-lights
1. add 5cm cubed of hydrogen peroxide into a boiling tube
2. add half a spatula of magnesium dioxide into the boiling tube
3. light a splint and gently blow it so that it is glowing but has no flame.
4. hold that splint at the mouth of the boiling tube. the splint should re-light
how do you test for chlorine gas. list the steps
damp litmus paper test
1. hold a piece of the damp litmus paper in the gas
2. if it goes white (bleached) then it is chlorine gas
how can you test for positive metal ions
- by adding sodium hydroxide solution
- flame test
what metal ions can be tested by the flame test
lithium 1+
sodium 1+
potassium 1+
calcium 2+
copper 2+
what flame does lithium 1+ produce
crimson
what flame does sodium 1+ produce
yellow
what flame does potassium 1+ produce
lilac
what flame does calcium 2+ produce
orange-red
what flame does copper 2+ produce
blue
how do you setup a flame test
- Dip the nichrome loop in hydrochloric acid to clean
- put the nichrome loop into the flame of a Bunsen burner to clean
- dip the loop back into acid
- put the loop into the metal compound
- put the loop into the flame of the Bunsen burner
- record the flame colour change in a table and repeat the test
what metal ions work with the sodium hydroxide test
copper 2+
iron 2+
iron 3+
calcium 2+
magnesium 2+
aluminium 3+
what is another name for positive metal ions
cations
how do you setup a sodium hydroxide test
- add 1cm cubed of the cation to a test tube
- add 2cm cubed of sodium hydroxide to the test tube
- observe and record any changes
- further add 5cm cubed of sodium hydroxide
- observe and record any changes
what precipitate forms when copper 2+ is added to sodium hydroxide
blue precipitate
what precipitate forms when iron 2+ is added to sodium hydroxide
light green precipitate
what precipitate forms when iron 3+ is added to sodium hydroxide
brown precipitate
what precipitate forms when calcium 2+ is added to sodium hydroxide
white precipitate
what precipitate forms when magnesium 2+ is added to sodium hydroxide
white precipitate
what precipitate forms when aluminium 3+ is added to sodium hydroxide
white precipitate
what observations is made with excess sodium hydroxide
only 1 chemical reacts the others don’t. aluminium 3+ forms a white precipitate which then dissolves in excess sodium hydroxide
what is the test for negative ions
- carbonate test
- sulphate test
- halide test
what are negative ions also known as
anions
how do you setup a carbonate test for anions
- place 1cm cubed of the sodium solutions into separate test tubes
- add 2cm cubed of lime water into a separate test tube
- add 1cm cubed of hydrochloric acid into each sodium solution test tube
- if there is effervescence then collect the gas using a pipette
- place the gas into the lime water and if it turns cloudy then it is C02 gas
how do you set up a sulphate test for anions
- add 1cm cubed of sodium solutions into separate test tubes
- add a few drops of hydrochloric acid into each test tube
- then add 1cm cubed of barium chloride solution to each test tube
- a white precipitate should form if sulphate is present
how do you setup a halide test for anions
- add 1cm cubed of the sodium solutions into separate test tubes
- add a few drops of dilute nitric acid to each test tube
- add 1cm cubed of silver bitrate solution
- chloride should form a white precipitate, bromide should form a cream precipitate and iodide should form a yellow precipitate
what are qualitative methods of tests
tests which use observations
what are quantitative methods of tests
tests which rely on measurements
what does instrumental methods for analysis rely on
machinery
what are the advantages of instrumental methods of analysis
- rapid
- very sensitive
- accurate
- can be used on very small samples
what are the disadvantages of instrumental methods of analysis
- equipment is expensive
- equipment can only be used by specialists
- gives results that can often be interpreted only by comparison with data from known substances
what is flame emission spectroscopy used for
analysing metal ions in solutions
how does flame spectroscopy work
- the sample is placed into a flame
- the light given out is passed through a spectroscope
- the light is analysed once passed through the spectroscope
- each element emits different light so the compound is split up into the different colours made by the elements in the ion and can be used to measure their concentration.
