Chemistry Quiz: Stoichiometry MCQs

Explanation
Sulphur is a correct option as it is a more non-polar compound. We can eliminate glucose as it is polar compound due to  presence of OH group in it and more soluble in polar solvent. lithium fluoride is also more polar due to ionic nature. Graphite, despite of having strong covalent bonds among carbon atoms, has free electrons that create attraction with polar solvent molecules.

Explanation
Although, both K2Cr2O7 and KMnO4 are commonly used in redox titration. But correct option is KMnO4 is most appropriate option as it changes its color at its end point

Explanation
Spectroscopy is a technique that involves the interaction of electromagnetic radiation with matter. It can be used to determine the equilibrium constant for a reaction by measuring the absorbance or emission of light by the reactants or products. In the case of the reaction between Fe2+ and SCN-1, spectroscopy can be used to measure the absorbance or emission of light by the Fe(SCN)2+ complex, which is formed in the reaction. By measuring the intensity of the light at different wavelengths, the concentration of the complex can be determined, and from that, the equilibrium constant can be calculated.

Explanation
NaHCO3, also known as sodium bicarbonate, is the compound that produces a gas at 25oC that is more dense than air. When NaHCO3 reacts with dilute HCl, it produces carbon dioxide gas (CO2), which is denser than air.

Explanation
The molarity of a solution can be calculated using the formula:

Molarity (M) = moles of solute / volume of solution in liters

In this question, we are given the volume of the Ba(OH)2 solution (20.00 mL) and the volume of HCl used (27.15 mL). Since the reaction between Ba(OH)2 and HCl is 1:2, we can conclude that the moles of HCl used is twice the moles of Ba(OH)2.

To find the moles of HCl used, we can use the formula:

moles = molarity x volume (in liters)

moles of HCl = 0.245 M x 0.02715 L = 0.00664875 moles

moles of Ba(OH)2 = 0.00664875 moles / 2 = 0.003324375 moles

Now, we can calculate the molarity of the Ba(OH)2 solution using the formula:

Molarity (Ba(OH)2) = moles of Ba(OH)2 / volume of solution in liters

Molarity (Ba(OH)2) = 0.003324375 moles / 0.02000 L = 0.166 M

Therefore, the molarity of the Ba(OH)2 solution is 0.166 M.

Explanation
Ionic hydride is a compound that contains a hydrogen ion (H+) and a negatively charged ion. When it reacts with water, the hydrogen ion from the ionic hydride combines with a hydroxide ion (OH-) from water to form water (H2O) and a basic solution. At the same time, the negatively charged ion from the ionic hydride combines with a positively charged ion from water to form a salt. Therefore, the reaction results in the formation of a basic solution and hydrogen gas.

Explanation
In a solution of Na3PO4, each molecule of Na3PO4 dissociates into 3 Na+ ions. Therefore, to calculate the number of moles of Na+ ions, we need to multiply the concentration of Na3PO4 by the number of Na+ ions per molecule. In this case, the concentration of Na3PO4 is 0.40 M, and since there are 3 Na+ ions per molecule, the number of moles of Na+ ions is 0.40 M * 3 * 0.020 L = 0.024 moles.

Explanation
The correct answer is 72.0 because in Al2SO4.18H2O, there are a total of 18 water molecules (H2O), each containing 2 hydrogen atoms and 1 oxygen atom. Therefore, there are a total of 18 * 1 = 18 oxygen atoms in the compound. The molar mass of Al2SO4.18H2O is 666.43 g/mol. The molar mass of the 18 oxygen atoms is 18 * 16 = 288 g/mol. Therefore, the percentage of oxygen (by mass) in Al2SO4.18H2O is (288 g/mol / 666.43 g/mol) * 100% = 72.0%.

Explanation
The molar mass of O2 is approximately 32 g/mol. To find the number of O2 molecules in 2.5 g, we can use the formula: number of moles = mass / molar mass. Plugging in the values, we get: number of moles = 2.5 g / 32 g/mol = 0.078125 mol. Since 1 mole of any substance contains 6.022 × 10^23 molecules (Avogadro's number), we can multiply the number of moles by Avogadro's number to find the number of molecules: 0.078125 mol × 6.022 × 10^23 molecules/mol ≈ 4.7 × 10^22 molecules. Therefore, the correct answer is 4.7 × 10^22.