Q1. Ans is indeed A. Under standard conditions, oxygen exists as
molecular dioxygen, so that's a molar mass of 32g, which means
there are 0.5 moles of He and 0.5 moles of O2.
Q2. Ans is indeed B. CuO is basic and will reduce the molarity
of protons in the solution, which would decrease the rate of
reaction between protons and Zn. Pressure doesn't affect rate of
reaction unless one or both reactants are gaseous.
Q3. The question is erroneous. It shouldn't be a weak "alkali",
but a weak "base". The two terms mean slightly different things.
Now that that's out of the way, the question setter intends the
answer to be D because Pb2+ reacts with a low molarity of OH- ions
to generate a white ppt of Pb(OH)2(s). In high molarity
and/or with excess OH- ions, the Pb(OH)2 is reacted away to
form the soluble complex ion : tetrahydroxoplumbate(II) ion
[Pb(OH)4]2-(aq).
Q4. Ans is Grp V, the element is nitrogen. However, 'O' level
students would not be expected to be able to answer this question.
At 'O' levels, when so many different oxidation states are
possible, the element should be a transition metal. Some of the
nitrogen-containing compounds with the various OSes are Mg3N2, NO,
NO2, N2O, N2O3. N2O4, N2O5, HNO2, HNO3, etc.
Q5. Ans is indeed A. Nuclear energy is hazardous, but does not
generate as much CO2 as burning fossil fuels to generate electrical
energy. Catalytic converters convert highly toxic CO to
(relatively) non-toxic CO2, but indirectly contributing slightly to
global warming.
What is the ratio of the vol of 2g of helium to the volume of
16g of oxygen, both vols at rtp?
A) 1 to 1
B) 1 to 2
C) 1 to 8
D) 2 to 1
My ans is D but ans given is A
Zinc reacts with dilute h2so4 to form zinc sulphate and hydrogen
gas. Which of these would reduce rate of reaction?
A) Add copper(ii) oxide to the reacting mixture
B) Reduce the pressure of the rxn
C) Stir the reacting mixture
D) Use excess zinc
My ans is B but ans given is A
Which of the following statement is true of a weak alkali?
A)it gives co2 gas when warmed with ammonium carbonate soln
B) it has a ph of 7.0
C)it reacts with hcl to form a salt only
D)it reacts with lead(ii) nitrate to form a white ppt
Why is ans given to be D
An element has oxiation states -3,+1,+2,+4,+5 in its cpds. Which
grp in periodic table is this element likely to be in?
A)ii
Biii
C)iv
D)v
Which of the following does not help to prevent global
warming?
A) Fit catalytic converters to car exhausts
B)Reduce co2 emissions in factories
C)Use nuclear energy
D) Use hydrogen fuel cells to power vehicles
My ans is C but ans given to be A