chem questions Flashcards
Separate unlabelled solid samples of three anhydrous sodium compounds are
provided for a student to identify.
These compounds are known to be sodium carbonate, sodium fluoride and
sodium chloride but it is not known which sample is which.
Outline a logical sequence of test-tube reactions that the student could carry out to
identify each of these compounds.
Include the observations the student would expect to make.
Give equations, including state symbols, for any reactions that would take place.
a Add named acid to all 3
1b Add water / make into a solution
1c Add AgNO3
2a Na2CO3 will fizz with acid
2b NaCl gives white ppt with AgNO3
2c NaF shows no (visible) change / no ppt
Silicon tetrafluoride (SiF4) is a tetrahedral molecule.
Deduce the type of intermolecular forces in SiF4
Explain how this type of intermolecular force arises and why no other type of
intermolecular force exists in a sample of SiF4
Van der Waals forces
one molecule induces dipole in
neighbouring/another/nearby molecule
symmetrical molecule / dipoles cancel
Suggest how the students’ method, and the analysis of the results, could be
improved in order to determine a more accurate value for the enthalpy of
reaction.
Justify your suggestions.
1a Insulate the beaker or use a polystyrene cup or a
lid
1b To reduce heat loss
2a Record the temperature for a suitable time before
adding the metal
2b To establish an accurate initial temperature
OR
2c Record temperature values at regular time intervals
2d To plot
Extrapolate the cooling back to the point of addition
Explain how permanent dipole-dipole forces arise between hydrogen chloride
molecules.
Difference in electronegativity leads to bond polarity
there is an attraction between ∂+ on one molecule and ∂- on
another
state one advantage of using a conical flask rather than a beaker for the titration
less chance of splashing
explain why the melting point of magnesium is higher vthan the nelting point of sodium
-mg2+ is smaller
-strong eelctrostatic forced between mg+and sea delocalised electrons
observation when dilute aqeuous naoh with mgcl2 and bacl2
white ppt
no observation
suggest why an excess of silver nitrate is used
to ensure thta all the halide ions are remooved fro the solution
observation when mg reacts with steam
bright light
mg+h20- mgo+h20
describe a further test to show whether solution c contains chloride or bromide ions
-dilute ammonia sol
-chlorate ions present then ti wiuld dissolve
-bromide. would nit
explain how forces arise between molecules of chlorine
-spontaneous movement of electrons in one molecule
-induces dipole in neighbouring molecules
-electropos and elecroneg temporayr attraction
rinsing buretter w deionised water before filling with naoh
what affevt
titre value would inc bc naoh more dilutr
suggest in terms of the intermolecular forces for eaach compound why cbr4 has a higher bp than chbr3
-vdw between cbr4 stronger than vdw and indcued dipole in chbr3
desrcibe a series of tests that the student can use to show that solution c. contains ammonia sulfate
test with Ba(NO3)2
produces a white precipitate
test with NaOH and heat
hold damp pH paper over the test tube which will turn blue
explain why this air bubble inc the final burette reading of the rough titration
solution will fill gap
during the titration the studnet washed the sinide of the concial flask with some distilles water
suggest why this washing does not give an incorect result
doesn’t change the number of moles
another student required to make up 250cm3 of an aqueous solution thay contains a knwon mass of MHCO3. The student apparatus and practical details that the student shouldt prepare the solution
1)weigh sample bottle containing the solid on a balance
2)transfer to beaker and reweigh sample bottle
3)record diff in mass
4)add distilled water\5)stir
6)until all solid has dissolves
7)transfer to volumetric flask
8)make up 250cm3 and mark w water
9)invert
a solution of sdoium chlorate was added to colourless solution of potassium iodied suggest what is observed
-brwon
-due to iodine being oxidsed
why uv used in propagation
provides energy to break (covalent) bond in chlorine / Cl2 or
to form chlorine free radicals
importance of % yield
idea of getting as much product as possible in the reaction /
idea of efficient conversion of reactants to products
importance of % atom economy
idea of maximising the mass of reactants / atoms that ends up
in desired product or
explain the differences between structural isomerisms and stereoisomerism
structural isomers = molecules with same
molecular formula but different structure
1b stereoisomers = molecules with same
structural formula but different
arrangement of atoms in space
Stereoisomers
2a lack of rotation around C=C
2b structures of E- and Z-but-2-ene
2c correct identity of E and Z isomers
Structural isomers
3a different C chain, e.g. methylpropene &
but-1-ene / but-2-ene
3b different position of functional group e.g.
but-1-ene & but-2-ene
3c different functional group, e.g.
cyclobutane & but-1-ene / but-2-ene /
methylpropene
ethanedioic acid is formed by the oxidation of ethane -1 2-diol
suitable reagent and conditions
conc sulfuric acid
reflux
Which statement is correct about thermal cracking?
[1 mark]
A A pressure between 100 and 200 kPa is used.
B Aromatic hydrocarbons are the major products.
C C–C bonds are broken.
D Zeolite catalysts are used.
c
Which statement is not correct about ozone?
[1 mark]
A It absorbs harmful ultraviolet radiation in the upper atmosphere.
B It decomposes to form oxygen.
C Its decomposition is catalysed by chlorine molecules.
D Ozone holes are regions of the upper atmosphere where there
is a reduced concentration of ozone.
c
Which can be used to distinguish between these two compounds?
(CH3)2CHCH2CHO and (CH3)3CCHO
[1 mark]
A Acidified potassium dichromate(VI)
B Fingerprint region of infrared spectrum
C Mr value in high resolution mass spectrometry
D Tollens’ reagent
b
An excess of methane reacts with chlorine in the presence of ultraviolet radiation.
What are the main products of this reaction?
[1 mark]
A CCl4 and H2
B CCl4 and HCl
C CH3Cl and H2
D CH3Cl and HCl
d
Which statement is correct about the production and use of ethanol as a biofuel?
[1 mark]
A Biofuel ethanol is produced by the fermentation of glucose in the
presence of yeast and air.
B Biofuel ethanol is purified by fractional distillation.
C No carbon dioxide is released when biofuel ethanol is burned.
D Biofuel ethanol burns with a cleaner flame than ethanol made by
hydration of ethene.
b
Which statement about the molecules in a sample of a gas is correct?
[1 mark]
A At a given temperature they all move at the same speed.
B At a given temperature their average kinetic energy is constant.
C As temperature increases, there are more molecules with the
most probable energy.
D As temperature decreases, there are fewer molecules with the
mean energy
b
highest ionisation energy in group 3
argon
products of mg and steam
mgo
h2
bright white light
white powder
least soluble group 2 sulphate and what’s it used for
baso4
x rays
diference in cf4 and xef4
square planar- 90,4 bp , 2lp ,lone pairs repel more than bonding pairs
tetrahedral-109.5,electrons pair repel equally 4bp
similarity and difference in reactions between sulphuric acid and sodium bromide
form h halides
br redox
meaning of electron impact ionisation
fired at high energy electrons to knock of an electron
fraction meaning
mixture of compounds with similar bp
carbon neutral
no net co2 emissions
why iodobutane faster reaction than bromobutane
c-i weaker c-br
why major rpdocut more than minor
-primary ,secondary structure , more stable carbocation, more electrons releasing alkyl group
why c cl bonds polar
difference in electronegativity
why molecules non [olar
symmetrical
dipoles cancel each other out
why tetrachlromethane high bp than di
-stronger vow than vow and induced dipole
-more electrons
explain why water should enter the condenser at the bottom and not top
ending condenser fills with water
-condenser cooler
Compounds A, B and C all have the molecular formula C5H10
A and B decolourise bromine water but C does not.
B exists as two stereoisomers but A does not show stereoisomerism.
Use this information to deduce a possible structure for each of compounds
A, B and C and explain your deductions.
State the meaning of the term stereoisomers and explain how they arise in
compound B.
1a states that A & B are unsaturated / do contain C=C / alkenes (this can be
obtained from the structures)
1b as they decolourise bromine water
1c states that C is saturated / does not contain C=C / is (cyclo)alkane (this can be
obtained from the structures)
1d as it does not decolourise bromine water
suggests suitable name/structure for A
pent-1-ene,
B = pent-2-ene
suggests a suitable name/structure of C (cyclopentane
explains what stereoisomerism is in terms of molecules with the same structural
formula but a different arrangement of atoms/bonds/groups in space
3b explains how it arises by discussing that C=C cannot rotate
Suggest one reason, other than the use of mean bond enthalpies, why a value fo
alkane is not gaseous
The student used a wash bottle containing deionised water when approaching the
end-point to rinse the inside of the conical flask.
Explain why this improved the accuracy of the titration
Idea that it ensures all ethanedioic acid / acid / sodium hydroxide /
alkali / reactants are in the mixture / solution / reaction
When 1-bromo-2-methylpropane reacts with hot, concentrated ethanolic
potassium hydroxide rather than dilute aqueous sodium hydroxide, a different
product is formed.
Name this organic product and name the mechanism for this reaction.
methyl propene
