75 free MCQs on Some Basic Concepts of Chemistry, each with its own worked answer and explanation. The mole is chemistry's counting unit. Learn to relate mass, volume, and number of particles using Avogadro's number and molar mass, the foundation of all stoichiometry and reaction calculations.
Take the timed Some Basic Concepts of Chemistry chapterwise test →75 practice questions on Some Basic Concepts of Chemistry, sorted Easy → Hard. Try each one first, then open its answer page for the worked explanation. Want the full theory first? Read the Some Basic Concepts of Chemistry notes.
Mass connects to moles via molar mass, and moles connect to particle count via Avogadro's number or to gas volume via the 22.4 L/mol rule at STP.
Q1.
The law of conservation of mass, which states that mass can neither be created nor destroyed in a chemical reaction, was proposed by:
Q2.
According to the law of definite proportions, a given chemical compound always contains its constituent elements combined in a fixed proportion by:
Q3.
Which of the following is an intensive property that does not depend on the amount of substance present?
Q4.
Avogadro's law states that equal volumes of all gases under the same temperature and pressure contain an equal number of:
Q5.
The sum of the mole fractions of all the components present in a solution is always equal to:
Q6.
What is one mole of any substance equal to?
Q7.
What is Avogadro's number?
Q9.
How many molecules are present in 1 mole of water?
Q10.
What is the molar mass of water, H<sub>2</sub>O?
Q11.
How many moles are present in 18 g of water?
Q12.
What formula is used to calculate number of moles from mass?
Q13.
What is the molar mass of carbon dioxide, CO<sub>2</sub>?
Q14.
How many moles are present in 44 g of CO<sub>2</sub>?
Q16.
How many litres are occupied by 2 moles of a gas at STP?
Q17.
The molar mass of oxygen gas, O<sub>2</sub>, is:
Q18.
How many moles are present in 32 g of oxygen gas, O<sub>2</sub>?
Q19.
What is the molar mass of NaCl?
Q20.
How many moles are present in 58.5 g of NaCl?
Q21.
Which quantity connects mass and number of particles?
Q22.
How many atoms are present in 1 mole of helium?
Q23.
What is the molar mass of methane, CH<sub>4</sub>?
Q24.
How many moles are present in 16 g of methane, CH<sub>4</sub>?
Q25.
In a balanced chemical equation, coefficients represent the ratio of:
Q26.
Chlorine occurs as two isotopes, <sup>35</sup>Cl (75%) and <sup>37</sup>Cl (25%). Its average atomic mass is:
Q27.
Carbon forms two oxides, CO and CO<sub>2</sub>. For a fixed mass of carbon, the masses of oxygen that combine are in the simple whole-number ratio:
Q28.
What is the molality of a solution prepared by dissolving 8 g of NaOH (molar mass 40 g mol<sup>-1</sup>) in 500 g of water?
Q29.
A solution contains 1 mole of water and 4 moles of ethanol. The mole fraction of ethanol in the solution is:
Q30.
What volume of water must be added to 100 mL of 0.5 M HCl to dilute it to 0.1 M?
Q31.
How many moles are present in 90 g of water?
Q32.
How many molecules are present in 2 moles of CO<sub>2</sub>?
Q33.
How many moles are present in 11.2 L of a gas at STP?
Q34.
What is the mass of 0.5 mole of CO<sub>2</sub>?
Q35.
How many atoms are present in 2 moles of helium?
Q36.
What is the molar mass of calcium carbonate, CaCO<sub>3</sub>?
Q37.
How many moles are present in 100 g of CaCO<sub>3</sub>?
Q38.
What is the mass of 3 moles of oxygen gas, O<sub>2</sub>?
Q39.
How many moles are present in 3.01 x 10<sup>23</sup> molecules?
Q40.
How many molecules are present in 9 g of water?
Q41.
What volume will 0.25 mole of a gas occupy at STP?
Q42.
In the reaction 2H<sub>2</sub> + O<sub>2</sub> -> 2H<sub>2</sub>O, the mole ratio of H<sub>2</sub> to O<sub>2</sub> is:
Q43.
How many moles of H<sub>2</sub>O are formed from 2 moles of H<sub>2</sub> in 2H<sub>2</sub> + O<sub>2</sub> -> 2H<sub>2</sub>O?
Q44.
What is the molar mass of sulfuric acid, H<sub>2</sub>SO<sub>4</sub>?
Q45.
How many moles are present in 49 g of H<sub>2</sub>SO<sub>4</sub>?
Q46.
The number of significant figures in the measurement 0.00206 is:
Q47.
How many moles are present in 22 g of carbon dioxide (CO₂)?
Q48.
The molarity of a solution containing 0.5 mol of solute in 250 mL of solution is:
Q49.
Which 1 g sample contains the greatest number of molecules?
Q50.
The percentage by mass of nitrogen in ammonia (NH₃) is:
Q51.
A compound contains 40% C, 6.7% H and 53.3% O by mass and has a molar mass of 180 g mol<sup>-1</sup>. Its molecular formula is:
Q52.
For the reaction N<sub>2</sub> + 3H<sub>2</sub> -> 2NH<sub>3</sub>, if 1 mole of N<sub>2</sub> is mixed with 2 moles of H<sub>2</sub>, the limiting reagent is:
Q53.
In a reaction the theoretical yield of a product is 25 g, but only 20 g is actually obtained. The percentage yield is:
Q54.
The molarity of pure water, taking its density as 1 g mL<sup>-1</sup>, is approximately:
Q55.
What volume of O<sub>2</sub> at STP is required for the complete combustion of 2.2 g of propane? (C<sub>3</sub>H<sub>8</sub> + 5O<sub>2</sub> -> 3CO<sub>2</sub> + 4H<sub>2</sub>O)
Q56.
How many grams of CO<sub>2</sub> contain 3.011 x 10<sup>23</sup> molecules?
Q57.
How many oxygen atoms are present in 1 mole of CO<sub>2</sub> molecules?
Q58.
How many moles of oxygen atoms are present in 2 moles of H<sub>2</sub>SO<sub>4</sub>?
Q59.
In N<sub>2</sub> + 3H<sub>2</sub> -> 2NH<sub>3</sub>, how many moles of NH<sub>3</sub> form from 1 mole of N<sub>2</sub>?
Q60.
In N<sub>2</sub> + 3H<sub>2</sub> -> 2NH<sub>3</sub>, how many moles of H<sub>2</sub> are needed for 2 moles of N<sub>2</sub>?
Q61.
What mass of CaCO<sub>3</sub> is needed to produce 44 g of CO<sub>2</sub> in CaCO<sub>3</sub> -> CaO + CO<sub>2</sub>?
Q62.
How many moles of O<sub>2</sub> are needed to burn 2 moles of CH<sub>4</sub> in CH<sub>4</sub> + 2O<sub>2</sub> -> CO<sub>2</sub> + 2H<sub>2</sub>O?
Q63.
What mass of water is formed when 4 g of hydrogen reacts completely with oxygen? Use 2H<sub>2</sub> + O<sub>2</sub> -> 2H<sub>2</sub>O.
Q64.
How many moles of atoms are present in 1 mole of H<sub>2</sub>O molecules?
Q65.
Which sample contains the greatest number of molecules?
Q66.
How many moles of ions are produced when 1 mole of NaCl dissolves completely in water?
Q67.
What volume of CO<sub>2</sub> at STP is produced from 0.5 mole of CaCO<sub>3</sub> in CaCO<sub>3</sub> -> CaO + CO<sub>2</sub>?
Q68.
What is the mass of 0.25 mole of H<sub>2</sub>SO<sub>4</sub>?
Q69.
How many hydrogen atoms are present in 2 moles of CH<sub>4</sub> molecules?
Q70.
A compound has molar mass 60 g/mol. How many molecules are in 30 g of it?
Q71.
A compound contains 80% carbon and 20% hydrogen by mass. Its empirical formula is:
Q72.
How many grams of NaOH are required to prepare 500 mL of a 0.1 M solution? (NaOH = 40)
Q73.
When 4 g of H₂ reacts with 16 g of O₂ (2H₂ + O₂ → 2H₂O), the limiting reagent is:
Q74.
The vapour density of a gas is 32. Its molar mass is:
Q75.
If 0.25 mol of an element weighs 16 g, its atomic mass is:
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