Stoichiometry — Part 1 MCQs with Explanations

The molecular weight of NH 3 is 17 g/mol (Nitrogen = 14, Hydrogen = 1 × 3 = 3). For 8.5 grams of NH 3 , the number of moles is calculated as: Moles of NH 3 = 8.5 / 17 = 0.5 moles. The total number of molecules in 0.5 moles is: 0.5 × 6.02 × 10 23 molecules. Since each molecule of NH 3 contains 4 atoms (1 nitrogen and 3 hydrogen), the total number of atoms is: 0.5 × 6.02 × 10 23 × 4 = 12.04 × 10 23 atoms.

According to Gay-Lussac's Law , for a gas at constant volume, the pressure is directly proportional to the absolute temperature: P ∝ T. First, convert the given temperatures to Kelvin: Initial temperature (T₁): 27°C + 273 = 300 K Final temperature (T₂): 300°C + 273 = 573 K Using the formula P₂ = P₁ × (T₂ / T₁) : P₂ = P₁ × (573 / 300) ≈ P₁ × 1.91 This shows that the final pressure is approximately 1.91 times the initial pressure, which is nearly double. Therefore, the pressure exerted is best described as doubled .

The pH scale measures the acidity or alkalinity of a solution, ranging from 0 (most acidic) to 14 (most alkaline), with 7 being neutral. A solution with pH 2 (A₁) is strongly acidic, since it is much lower than 7. A solution with pH 6 (A₂) is slightly acidic, as it is just below neutral. Therefore, A₁ is highly acidic compared to A₂. Option A is incorrect because A₁ is not alkaline at all, and Option C is incorrect because pH 2 indicates strong acidity, not slight acidity. Hence, the correct interpretation is that A₁ is highly acidic .

According to the ideal gas law , for a fixed amount of gas: PV = nRT Since the amount of gas (n) and gas constant (R) stay constant, the relationship between volume, temperature, and pressure is: V ∝ T/P You are doubling the absolute temperature (T₂ = 2T₁), and at the same time reducing the pressure to half (P₂ = 0.5P₁). So, the new volume compared to the original volume will be: V₂/V₁ = (T₂/T₁) * (P₁/P₂) Substituting the values gives: V₂/V₁ = (2T₁/T₁) * (P₁/0.5P₁) V₂/V₁ = 2 * 2 = 4 Therefore, the volume of the gas will experience a four fold increase , not just doubling.

350 is the correct answer to “A sample of well water contains 140 gm/m 3 Ca 2+ ions and 345 gm/m 3 Na + ions. The hardness of the sample of water, expressed in terms of equivalent CaCO 3 in gm/m 3 is (assuming atomic masses of Ca : 40, Na : 23, C : 12, O : 16)”. This question is standard in competitive examination syllabi for Stoichiometry.

Kinetic energy is the correct answer to “The molecules of a liquid which is in equilibrium with its vapor at its boiling point on an average have equal __________ in the two phases.”. This question is standard in competitive examination syllabi for Stoichiometry.

Both B and C is the correct answer to “Which of the following holds good for a solution obeying Raoult's law (i.e., an ideal solution) (where, ΔH = heat of mixing, and ΔV = volume change on mixing )”. This question is standard in competitive examination syllabi for Stoichiometry.

Molality is the correct answer to “Number of gm moles of solute dissolved in 1 kg of solvent is called its”. This question is standard in competitive examination syllabi for Stoichiometry.

6 is the correct answer to “If pH value of a solution is 8, then its pOH value will be”. This question is standard in competitive examination syllabi for Stoichiometry.

Same elevation in boiling point is the correct answer to “Solution made by dissolving equimolar amounts of different solutes in the same amount of a given solvent will have the”. This question is standard in competitive examination syllabi for Stoichiometry.

Kopp's rule is the correct answer to “For estimation of heat capacity of a solid compound, one can use”. This question is standard in competitive examination syllabi for Stoichiometry.

None of these is the correct answer to “Dissolving a solute in a solvent does not change its”. This question is standard in competitive examination syllabi for Stoichiometry.

One allotropic form to another allotropic form is the correct answer to “Heat of transition is the heat evolved or absorbed, when a substance is converted from”. This question is standard in competitive examination syllabi for Stoichiometry.

Solid is the correct answer to “__________ fuels require the maximum percentage of 'excess air' for complete combustion.”. This question is standard in competitive examination syllabi for Stoichiometry.

Kinetic energy is the correct answer to “A liquid is in equilibrium with its vapor at its boiling point. On an average, the molecules in the liquid and gaseous phases have equal”. This question is standard in competitive examination syllabi for Stoichiometry.

0.13 is the correct answer to “The vapour pressure of water is given by, in P sat = A - (5000/T), where A is a constant, Psat is the vapour pressure in atm. and T is the temperature in K.The vapor pressure of water in atm. at 50°C is approximately”. This question is standard in competitive examination syllabi for Stoichiometry.

Antonic equation is the correct answer to “An equation for calculating vapour pressure is given by, log 10 P = A - B(t + c). This is called the”. This question is standard in competitive examination syllabi for Stoichiometry.

-109.5 is the correct answer to “The combustion equations of carbon and carbon monoxide are as follows: C + O 2 = CO 2 , ΔH = -394 kJ/kg.mole CO + $$\frac{1}{2}$$O 2 = CO 2 , ΔH = -284.5 kJ/kg.mole The heat of formation of CO is __________ kJ/kg.mole.”. This question is standard in competitive examination syllabi for Stoichiometry.

Both A & B is the correct answer to “In case of a ternery system involving two liquid components and a solute, the ratio of the concentration of the solute in the two phases at equilibrium is called the distribution co-efficient. The distribution co-efficient depends upon the”. This question is standard in competitive examination syllabi for Stoichiometry.

44/22.4 is the correct answer to “Density of carbon dioxide is __________ kg/Nm 3 .”. This question is standard in competitive examination syllabi for Stoichiometry.

Complete wetting is the correct answer to “Enthalpy change resulting, when unit mass of solid is wetted with sufficient liquid, so that further addition of liquid produces no additional thermal effect, is called the heat of”. This question is standard in competitive examination syllabi for Stoichiometry.

Kopp's rule is the correct answer to “The heat capacity of a solid compound is calculated from the atomic heat capacities of its constituent elements with the help of the”. This question is standard in competitive examination syllabi for Stoichiometry.

$$\frac{8}{9}$$ is the correct answer to “Equal masses of CH 4 and H 2 are mixed in an empty container. The partial pressure of hydrogen in this container expressed as the fraction of total pressure is”. This question is standard in competitive examination syllabi for Stoichiometry.

Is a function of the liquid phase composition is the correct answer to “The activity co-efficient of a solution, which accounts for the departure of liquid phase from ideal solution behaviour”. This question is standard in competitive examination syllabi for Stoichiometry.

Forces operative between its molecules are negligible is the correct answer to “An ideal gas can be liquified, because”. This question is standard in competitive examination syllabi for Stoichiometry.

Both B & C is the correct answer to “The value of the gas-law constant 'R' is 1.987”. This question is standard in competitive examination syllabi for Stoichiometry.

22.4 litres is the correct answer to “Volume occupied by one gm mole of a gas at S.T.P. is”. This question is standard in competitive examination syllabi for Stoichiometry.

6.023 x 107 is the correct answer to “The number of H + in 1 c.c solution of pH 13 is”. This question is standard in competitive examination syllabi for Stoichiometry.

1500 is the correct answer to “The density of a liquid is 1500 kg/m 3 . Its value in gin/litre will be equal to”. This question is standard in competitive examination syllabi for Stoichiometry.

0.19 is the correct answer to “One mole of methane undergoes complete combustion in a stoichiometric amount of air. The reaction proceeds as CH 4 + 2O 2 → CO 2 + 2H 2 O. Both the reactants and products are in gas phase. ΔH° 298 = -730 kJ/mole of methane. Mole fraction of water vapour in the product gases is about”. This question is standard in competitive examination syllabi for Stoichiometry.

0.5 < Xw < 1.0 is the correct answer to “The boiling points for pure water and pure toluene are 100°C and 110.6°C respectively. Toluene and water are completely immiscible in each other. A well agitated equimolar mixture of toluene and water are prepared. If, at a total pressure of one standard atm. exerted by the vapours of water and toluene, the mole fraction of water X w in the vapour phase satisfies”. This question is standard in competitive examination syllabi for Stoichiometry.

k.mole/m2.s is the correct answer to “Pure aniline is evaporating through a stagnant air film of 1 mm thickness at 300 K and a total pressure of 100 KPa. The vapor pressure of aniline at 300 K is 0.1 KPa. The total molar concentration under these conditions is 40.1 mole/m 3 . The diffusivity of aniline in air is 0.74 × 10 -5 m 2 /s.The numerical value of mass transfer co-efficient is 7.4 × 10 -3 . The rate of evaporation of aniline is 2.97 × 10 -4 . Its units are”. This question is standard in competitive examination syllabi for Stoichiometry.

Superheated is the correct answer to “A vapor whose partial pressure is less than its equilibrium vapor pressure is called a __________ vapor.”. This question is standard in competitive examination syllabi for Stoichiometry.

105 is the correct answer to “One Newton is equal to __________ dynes.”. This question is standard in competitive examination syllabi for Stoichiometry.

0.6 is the correct answer to “The vapor pressure of the solvent decreased by 10 mm Hg, when a non-volatile solute was added to the solvent. The mole fraction of the solute in the solution is 0.2. What should be the mole fraction of the solvent, if the decrease in vapor pressure of the solvent is required to be 20 mm Hg.”. This question is standard in competitive examination syllabi for Stoichiometry.

13360 is the correct answer to “The average value of heat of neutralisation of dilute solution of strong acids and strong bases is about __________ kcal/kg.mole of water formed.”. This question is standard in competitive examination syllabi for Stoichiometry.

Formation is the correct answer to “The heat change for the reaction, C(s) + 2S(s) → CS 2 ($$l$$), is 104.2 kJ. It represents the heat of”. This question is standard in competitive examination syllabi for Stoichiometry.

Hess is the correct answer to “Which of the following is not used for computing latent heat of vaporisation”. This question is standard in competitive examination syllabi for Stoichiometry.

Henry's is the correct answer to “The equilibrium value of the mole fraction of the gas dissolved in a liquid is directly proportional to the partial pressure of that gas above the liquid surface. This statement pertaining to the solubility of gases in liquid is the __________ law.”. This question is standard in competitive examination syllabi for Stoichiometry.

2.5 is the correct answer to “2 litres of nitrogen at N.T.P. weighs __________ gms.”. This question is standard in competitive examination syllabi for Stoichiometry.