Practice questions Flashcards
A sample of Gallium consists of two isotopes, Ga-69 and Ga-71. The RAM of the sample was found to be 69.7. Calculate the percentage abundance of each isotope.
65% Ga-69 and 35% Ga-71
working: 69.7 = ((69x + 71(100-x))/100
x = 65
How many neutrons does the isotope boron-11 have?
6
working: 11 - 5
Which of the molecules have the strongest intermolecular forces? BF3, H2S, NH3 or H2
NH3
reason: hydrogen bonding
Which structure would sulfur, S8, have?
simple covalent lattice
What is used as the standard measurement of relative isotopic mass?
carbon-12
Give the meaning of ‘isotopes’
atoms with the same number of protons but different numbers of neutrons
Explain how a student could analyse a TLC chromatogram to identify alpha-amino acids present.
calculate Rf values and compare to a database of known values
Suggest why alpha-amino acids with similar structures could cause problems when using TLC to analyse mixtures of alpha-amino acids.
may have similar Rf values
spots may merge together
Explain how GC-MS can be used to identify compounds.
separates compounds to produce fragmentation patterns which can be compared to a database
How does a liquid stationary phase separate organic compounds in a mixture in gas chromatography?
solubility
Which would have the longest retention time when using an alkane stationary phase in GC?
A) alkane
B) alcohol
C) ester
A) alkane
Explain what is meant by the term condensation polymerisation.
the joining of monomers to form a polymer chain with the loss of a small molecule such as H20 or HCl
Polyester x is a degradable polymer prepared by bacterial fermentation of sugars. State two ways polyester x can be degraded.
hydrolysis
photodegradable with sunlight/UV
State and the shape and bond angle around a carbon atom in the alkyl group of propanoic acid. Explain the shape.
shape = tetrahedral
bond angle = 109.5 degrees
explanation = 4 bonding pairs of electrons repelling as far apart as possible
When carrying out a titration, which piece of apparatus should be used to measure the 25cm3 portion of acid solution that has been made up in a volumetric flask?
graduated pipette
How can you reduce the effect of any random error in a titration?
repeat the titration until two concordant results are achieved
State 3 reasons why use of catalysts in industrial processes can be beneficial to the environment.
less energy required
lower carbon dioxide emissions
greater atom economy / less waste
Describe the bonding in silicon.
giant covalent lattice with strong covalent bonds
NO radicals catalyse the breakdown of ozone in the stratosphere. What two equations show how NO radicals catalyse this breakdown?
O3 + .NO -> O2 + NO2.
NO2. + O -> NO. + O2
What should there not be when heating an alcohol?
A naked flame (alcohols are flammable so a sand bath could be used instead of a Bunsen burner)
Explain, in terms of subatomic particles, the meaning of the term isotopes.
atoms of the same element with the same number of protons but with different numbers of neutrons, so with different atomic masses
The two isotopes of potassium have the same chemical properties. Why?
same number of electrons in the outer shell
A mass spectrometer measures the relative abundance of ions with different m/z values. Explain the meaning of ‘m’.
relative mass
What is the chemical name for bicarbonate of soda, NaHCO3?
sodium hydrogen carbonate