C17 - Chemical Analysis (PAPER 2) Flashcards
What is a pure substance
a substance containing only one type of element or compound
What is an impure substance
a mixture
Do pure or impure substances have specific melting and boiling points
Pure substances
What are formulations
- what are some examples
Mixtures of many components in specific proportions to make useful products
- fuels, cleaning agents, paints, alloys, fertilisers, foods
What is chromatography
a method to separate different components in a mixture
What is the Rf value
- What is the formula for it
- What does it stand for
a ratio of how far up the paper a certain spot moves compared to how far the solvent has
- distance moved by substance / distance moved by solvent
- retention factor
What is the link between Rf value and solubility
The higher the Rf value, the more soluble a substance is
How can you tell if a substance is pure from its chromatogram
It will only have one spot
What numbers are all Rf values between
0 and 1
What is the stationary phase in a chromatogram
the paper
What is the mobile phase in a chromatogram
the solvent
What is the solvent front
the top of where the solvent travels up the paper
What is the test for hydrogen gas
- What is the observation
hold a lighted splint near the gas
- hear a squeaky pop
What is the test for oxygen gas
- What is the observation
hold a glowing splint near the gas
- splint relights
What is the test for carbon dioxide gas
- What is the observation
bubble the gas through limewater
- the limewater turns milky (cloudy white)
What is the test for chlorine gas
- What is the observation
hold a piece of damp litmus near the gas
- bleaches the litmus white
What is the test for Aluminium cations ( Al [3+] )
- on slow addition of excess sodium hydroxide solution, white precipitate forms that eventually dissolves again with excess sodium hydroxide
What is the test for calcium cations ( Ca [2+] )
on addition of excess sodium hydroxide solution, white precipitate that doesn’t dissolve
What is the test for magnesium cations ( Mg [2+] )
on addition of excess sodium hydroxide solution, white precipitate that doesn’t dissolve
What is the test for copper (II) cations ( Cu [2+] )
forms a blue precipitate when NaOH is added
What is the test for iron (II) cations ( Fe [2+] )
forms a green precipitate when NaOH is added
What is the test for iron (III) cations ( Fe [3+] )
forms a brown precipitate when NaOH is added
What is a cation
a positively charged ion
What is an anion
a negatively charged ion
What is the test for a carbonate anion ( CO3 [2-] )
- What is the observation for a positive result
add dilute acid
- carbon dioxide gas formed which can be tested for with limewater
What is the test for a chloride anion ( Cl [-] )
- What is the observation for a positive result
add silver nitrate solution in the presence of nitric acid
- white precipitate formed
What is the test for a bromide anion ( Br [-] )
- What is the observation for a positive result
add silver nitrate solution in the presence of nitric acid
- cream precipitate formed
What is the test for a iodide anion ( I [-] )
- What is the observation for a positive result
add silver nitrate solution in the presence of nitric acid
- yellow precipitate formed
What is the test for a sulphate anion ( SO4 [2-] )
- What is the observation for a positive result
add barium chloride solution in the presence of hydrochloric acid
- white precipitate formed
What coloured flame does lithium produce whilst burning
crimson
What coloured flame does sodium produce whilst burning
yellow
What coloured flame does potassium produce whilst burning
lilac
What coloured flame does calcium produce whilst burning
orange - red
What coloured flame does copper produce whilst burning
green
What are the benefits of using instrumental analysis
they are rapid, accurate and sensitive
What are the drawbacks of using instrumental analysis
require training to use, comparing to records
What is flame emission spectroscopy
- how does it work
a type of instrumental analysis similar to a flame test
- the solution is put into a flame
- electrons move to outer shells
- When heating is stopped, energy is given off as the electrons move back to their original shells
- energy is given off as light
- This is passed through a spectroscope
- the instrument provides the exact wavelength of the light
- the wavelength can be compared to a reference to establish the identity of the sample
What is a flame test
a way of identifying metals by seeing what colour flame it produces whilst burning
