Key chemistry definitions that I need to memorise... Flashcards
Define the term relative atomic mass.
The mean mass of an atom of an element divided by 1/12th the mean mass of an atom of the carbon-12 isotope.
Give 2 reasons why it is necessary to ionise the isotopes of chromium before they can be analysed in a TOF mass spectrometer.
- Ions will be accelerated by an electric field.
- Ions create a current when hitting the detector.
Describe how the molecules are ionised using electrospray ionisation.
- The sample is dissolved in a volatile solvent.
- It is injected through a needle at a high voltage.
- Each molecule gains a proton.
Explain the pattern in first ionisation energies between Be and B.
- B is lower than Be, as the outer electron is in 2p.
- This is higher in energy than 2s.
Why is the third ionisation energy of Magnesium is much higher than the second ionisation energy of Mg.
An electron is being removed from a lower energy level, so the electron is less shielded.
What does the term ‘electronegativity’ mean?
The tendency for an atom to attract a pair of electrons.
Explain why CBr4 is not a polar molecule.
The molecule is completely symmetrical, so the dipoles cancel out.
In terms of the intermolecular forces for each compound, explain why CBr4 has a higher boiling point than CHBr3.
-CBr4 has van der Waals’ forces between moplecules.
- CHBr3 has van der Waal’s forces and dipole-dipole intermolecular forces.
- The van der Waals’ between CBr4 molecules are stronger than the dipole-dipole and van der Waals’ forces between CHBr3.
How is H2SO4 reduced?
Firstly, H2SO4 to SO2 (Colourless gas)
Secondly, reduced to S (Yellow solid
Then finally reduced to H2S. (Foul-smelling gas)
How can the observations from Test 1 and Test 2 be used to show that solution B contains hydrochloric acid?
Effervescence with sodium carbonate, so it contains H+ ions/is acidic. (Na2CO3)
- White ppt with Silver nitrate, so contains chloride ions. (AgNO3)
Describe a series of tests that the student can use to show that solution C contains ammonium sulfate.
Warm with NaOH.
- Damp red litmus paper at the mouth of the tube turns blue.
(Presence of ammonia).
- Add acidified BaCl2.
A white ppt should form.
(Shows presence of a sulfate).
Step 1 Add an excess of AgNO3(aq) to 10.0 cm3 of solution D.
Step 2 Filter, wash, dry and weigh the precipitate.
Step 3 Add an excess of dilute ammonia to the dry precipitate.
Step 4 Filter, wash, dry and weigh the solid that remains.
Explain how the masses recorded during this experiment can be used to show that solution D contains a mixture of halide ions.
- The second mass is smaller.
- AgCl dissolves in dilute ammonia.
Testing for an Aldehyde.
- Add tollens reagant.
- Add a few drops of tollens reagant to your solution.
- If an aldehyde is present, a silver mirror is present.
Testing for an Alcohol.
- Add acidified potassium dichromate to your test tubes.
- If an alcohol is present, the colour should change from orange to green.
Testing for an alkene/alkane.
- Add your solution into a test tube.
- Add bromine water.
- If the colour goes from orange to colourless, then an alkene is present.
- For alkanes, it should remain orange.
Testing for a carboxylic acid.
- Add one spatula of solid sodium hydrogencarbonate into a test tube.
- Add your solution into this same tube.
- When they come into contact, a strong effervescence indicates that a carboxylic acid is present.
- The bubbles that form are carbon dioxide.
Testing for a halogenoalkane.
- Heat up the solution to dissociate the halide ions.
- Add acidified silver nitrate to your solution.
- Complete further tests to confirm validity.
- White = chlorine.
- Cream = bromine.
- Yellow = iodine.
How can you distinguish compounds with the same functional group using IR spectroscopy?
- Use the finger-print region of the IR spectrum.
- Look for an exact match to spectra of known compounds. These are unique for every single compound.
