chem mcq questions.
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Just start my chemistry revision for my mid year exams,and yea....stuff taught last year i kinda forgotten. here are some chem mcq questions that i would want to ask for answers,preferbly with explainations too.some of them seems easy though...or even all of them.
1)The mass of one mole of a chloride formed by a metal Y is 74.5g.The formula of the chloride could be
A)YCl
B)YCl2
C)Y2Cl
D)Y2Cl2
2)Aluminium is higher up in the reactivity series than iron.however,iron rusts (reacts with air and water) buy aluminium does not.What is the reason for this?
A) An inert oxide coating formed on aluminium.
B)aluminium oxide is amphoteric.
C)Iron (II) oxide is water soluble.
D)Iron (III) oxide is a basic oxide.
3)Which metal has the least tendency to form positive ions?
A)Aluminium
B)sodium
C)calcium
D) copper
4)a piece of magnesium ribbon does not react when put into a solution of hydrogen chloride in methylbenzene,an organic solvent. Which change will cause this reaction to occur?
A)adding water and stirring.
B) ADding more methylbenzene.
C)stirring the mixture vigorously.
D)boiling the mixture.
5)In which compound is nitrogen in its lowest oxidation state?
A)N2O
B)NO
C)NO2
D)N2O2
These are all 'O' Level Pure chemistry mcq questions :)
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Q1.
This is a not a usual type of chem calculation question, since trial-and-error is required. However, because the molar mass of 74.5g isn't too large, the answer can be obtained by the average student within 30 seconds. The chloride is potassium chloride, KCl, molar mass 74.6g.
Another example of a similar question : which hydrocarbon has a molar mass of 26g? Ans : ethyne.
Q2.
This inert layer of metal oxide, is known as the "passivation layer", since it makes the metal relatively unreactive. (It's not that the metal oxide is totally unreactive, but just less reactive than the pure metal itself).
Q3.
The more reactive the metal, the more positive it's oxidation potential (see this table), the greater the tendency to form cations. Copper is the least reactive (standard oxidation potential of Cu to Cu2+ = -0.34V). Based on the standard redox potentials given in this table, (note : reduction potentials are given, oxidation potentials can be deduced by changing the +ve/-ve sign), can you deduce which is the most reactive metal among Al, Na and Ca? This could be asked at 'O' levels as a 'Data Based Qn'. Ans : Oxidation potentials of Al, Na and Ca are +1.66V, +2.71V and +2.87V. Accordingly, the most reactive metal (ie. the metal with the most positive oxidation potential) is Ca.
Q4.
'A' level answer :Acidic gases such as hydrogen halides (eg. hydrogen chloride) do not behave as (Bronsted-Lowry) acids, meaning they do not dissociate or donate H+ ions, when dissolved in non-polar, organic solvents such as methyl benzene. They remain as covalently bonded H-Cl molecules in such non-polar organic solvents. In contrast, with polar solvents (especially protic polar solvents) such as water, H-Cl molecules ionize (ie. form ions) by dissociating into H+ ions and Cl- ions. The H+ ions are actually present in the form of H3O+ ions (hydroxonium ions or hydronium ions). The reason for this different behaviour of hydrogen halides in non-polar solvents versus protic polar solvents, has to do primarily with enthalpy considerations (compare magnitudes of the exothermic ion-dipole interactions with the endothermic bond dissociation process) and to a smaller extent, entropy considerations.
'O' level answer :
Acids only behave as acids when dissolved in water.
Q5.
The 'O' level method for finding OS (Oxidation State), involves recognizing that "Ionic charge is the sum of atomic OSes". Let the OS of N be x. OS of each O atom is -2 (unless O is bonded to another O atom, or to more electronegative F atom, both of which is rarely asked at 'O' levels). Solve for x.
Eg. N2O2, we have 2x + 2(-2) = 0, hence x = +2
A)N2O has N with OS of +1
B)NO has N with OS of +2
C)NO2 has N with OS of +4
D)N2O2 has N with OS of +2
The 'A' level method : OS = Formal Charge + Electronegativity consideration.
Eg. N2O2, there are several resonance contributors we can use, most notably the following two :
Contributor #1
O atom doubly bonded to N atom singly bonded to N atom doubly bonded to O atom. For each of the N atoms, OS = Formal charge + Electronegativity consideration = (0) + (+2) = +2
Contributor #2
-ve O atom singly bonded to +ve N atom triply bonded to +ve N atom singly bonded to -ve O atom. For each of the N atoms, OS = Formal charge + Electronegativity consideration = (+1) + (+1) = +2
Originally posted by Blasst:Just start my chemistry revision for my mid year exams,and yea....stuff taught last year i kinda forgotten. here are some chem mcq questions that i would want to ask for answers,preferbly with explainations too.some of them seems easy though...or even all of them.
1)The mass of one mole of a chloride formed by a metal Y is 74.5g.The formula of the chloride could be
A)YCl
B)YCl2
C)Y2Cl
D)Y2Cl2
2)Aluminium is higher up in the reactivity series than iron.however,iron rusts (reacts with air and water) buy aluminium does not.What is the reason for this?
A) An inert oxide coating formed on aluminium.
B)aluminium oxide is amphoteric.
C)Iron (II) oxide is water soluble.
D)Iron (III) oxide is a basic oxide.
3)Which metal has the least tendency to form positive ions?
A)Aluminium
B)sodium
C)calcium
D) copper
4)a piece of magnesium ribbon does not react when put into a solution of hydrogen chloride in methylbenzene,an organic solvent. Which change will cause this reaction to occur?
A)adding water and stirring.
B) ADding more methylbenzene.
C)stirring the mixture vigorously.
D)boiling the mixture.
5)In which compound is nitrogen in its lowest oxidation state?
A)N2O
B)NO
C)NO2
D)N2O2
These are all 'O' Level Pure chemistry mcq questions :)
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thanks! now i gotta work doubly hard for my mid year exams! :D
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Gambatte!
