Multiple Choice QuestionsThe heat of combustion of carbon to CO2 is -395.5 kJ/mol. The heat released upon the formation of 35.2 g CO2 from carbon and oxygen gas is
-315 kJ
+315 kJ
-630 kJ
-630 kJ
A.
-315 kJ
20.0 g of a magnesium carbonate sample decomposes on heating to give carbon dioxide and 8.0 g magnesium oxide. What will be the percentage purity of magnesium carbonate in the sample? (Atomic weight of Mg =24)
75
96
60
60
D.
60
In the given problem we have a practical yield of MgO. For calculation of percentage yield of MgO. we need a therortical yield of MgO. For this, we shall use mole concept.
MgCO3(s) → MgO (s) + CO2(g) .. (i)
What is the pH of the resulting solution when equal volumes of 0.1 M NaOH and 0.01 M HCl are mixed?
12.65
2.0
7.0
7.0
A.
12.65
When equal volumes of acid and base are mixed then resulting solution become alkaline if the concentration of base is taken high.
Let normality of the solution after mixing 0.1 M
NaOH and 0.01 M HCl is N.
therefore, N1V1 - N2V2 = NV
or 0.1 x 1 - 0.01 x 1 = N x 2
Since normality, of NaOH, is more than that of HCl. Hence, the resulting solution is alkaline.
Or
[OH-] = N = 0.09/2 = 0.045 N
Or pOH = - log (0.045) = 1.35
therefore, pH = 14-pOH
= 14 - 1.35 = 12.65
What is the mass of precipitate formed when 50 mL of 16.9% solution of AgNO3 is mixed with 50 mL of 5.8% NaCl solution?
(Ag = 107.8, N = 14, O = 16, Na = 23, Cl = 35.5)
28 g
3.5 g
7 g
7 g
C.
7 g
For the calculation of the mass of AgCl precipitate, we find the mass of AgNO3 and NaCl in equal volume with the help of mole concept. 16.9% solution of AgNO3 means 16.9 g AgNO3 is present in 100 mL solution.
therefore, 8.45 g AgNO3 will present in 50 mL solution similarly,
5.8 g NaCl is present in 100 ml solution
A gas such as carbon monoxide would be most likely to obey the ideal gas law at
high temperatures and low pressures
low temperatures and high pressures
high temperatures and high pressures
high temperatures and high pressures
A.
high temperatures and low pressures
Real gases show ideal gas behaviour at high temperatures and low pressures.
PV = nRT
If Avogadro number NA, changed from 6.022 x 1023 mol-1 this would change
the definition of mass in units of grams
the mass of one mole of carbon
the ratio of chemical species to each other in the balanced equation
the ratio of chemical species to each other in the balanced equation
B.
the mass of one mole of carbon
If Avogadro number NA, is changed from 6.022 x 1023 mol-1 to 6.022 x 1020 mol-1 this would change the mass of one mole of carbon.
therefore,
1 mole of carbon has mass = 12 g
or 6.022 x 1023 atoms of carbon have mass = 12 g
therefore, 6.022 x 1020 atoms of carbon have mass
Which is the correct order of increasing energy of the listed orbitals in the atom of titanium?
3s 4s 3p 3d
4s 3s 3p 3d
3s 3p 3d 4s
3s 3p 3d 4s
C.
3s 3p 3d 4s
According to Aufbau rule
3s < 3p < 3d< 4s
Which one of the following pairs of the solution is not an acidic buffer?
HClO4 and NaClO4
CH3COOH and CH3COONa
H2CO3 and Na2PO4
H2CO3 and Na2PO4
A.
HClO4 and NaClO4
A buffer solution is one which resists changes in pH when small quantities of an acid or an alkali are added to it.
HClO4 and NaClO4 are not an acidic buffer because strong acid with its salt cannot form buffer solution.Decreasing order of stability of 
is
A.
order of stability directly proportional to the bond order
therefore, the order of the stability of given species,
The formation of the oxide ion O2- (g), from oxygen atom requires first an exothermic and then an endothermic step as shown below,
Thus, the process of formation of O2- in the gas phase is unfavourable even though O2- is isoelectronic with neon. It is due to the fact that
electron repulsion outweighs the stability gained by achieving a noble gas configuration
O- ion has comparatively smaller size that oxygen atom
oxygen is more electronegative
oxygen is more electronegative
A.
electron repulsion outweighs the stability gained by achieving a noble gas configuration
Electron repulsion predominates over the stability gained by achieving noble gas configuration. Hence, the formation of O2- in the gas phase is unfavourable.
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