Some Basic Concepts in Chemistry Mock Test – NEET Chemistry

1. Two isotope samples of the same element X are prepared. Each contains only isotopes of masses and .
Sample P consists of 50% of each isotope by number.
Sample Q consists of 25% of the lighter isotope and 75% of the heavier isotope by number.
Exactly 11.0 g of P is mixed with exactly 11.5 g of Q. What is the average atomic mass of X in the combined sample?

2. Four pure molecular substances are reported to have the same empirical formula, . Their separately measured molar masses are shown below.

Which conclusion follows if the empirical formula and molar-mass measurements are exact? (Atomic masses: C = 12, H = 1, O = 16)

3. A pure gaseous hydrocarbon is completely combusted. At a common reference temperature and pressure sufficiently high to keep the product water in the vapour phase, 1 L of the hydrocarbon produces 5 L of gaseous and 6 L of water vapour. The density of the hydrocarbon at the reference conditions is times that of pure oxygen gas at those same conditions. Assuming ideal-gas behaviour, what is the molecular formula of the hydrocarbon, and how many litres of oxygen are required to combust 1 L of it completely?

4. A mixture contains of formula units and of formula units. The two solids are mixed physically without undergoing reaction.
Consider the following statements.
Statement I: The combined amount of iron atoms is .
Statement II: The combined amount of oxygen atoms is .
Statement III: The mixture must have one definite empirical formula because both components contain only iron and oxygen.
Statement IV: The amount of chemical formula units in the mixture is , while the total amount of constituent atoms is greater.
Which statements are correct?

5. A non-reacting gaseous mixture is prepared from 16 g of methane and 44 g of carbon dioxide. Assume ideal-gas behaviour. What are the mole fraction of carbon dioxide, its mass fraction, and the average molar mass of the gaseous mixture? (Atomic masses: C = 12, H = 1, O = 16)

6. Two pure gaseous substances, and , react according to

A rigid vessel initially contains of hydrogen and of chlorine. Assume complete consumption of the limiting reactant, no other reactions, constant temperature and ideal-gas behaviour. Which pair correctly describes the ratio of final to initial pressure and the mole fraction of hydrogen in the final mixture?

7. A 0.50 mol sample of a hypothetical molecular gas is compared with a 0.50 mol sample of another molecular gas . The atomic molar masses of X and Y are and , respectively. Which statement correctly compares the total amounts of constituent atoms and the sample masses?

8. A solid mixture contains only sodium carbonate and sodium hydrogen carbonate. Increasing amounts of hydrochloric acid are added in separate trials.
The experimental conditions are specified so that the following reactions occur sequentially:
Stage I:

Stage II:

All original sodium carbonate is converted into sodium hydrogen carbonate before any Stage II reaction occurs. After Stage I, further acid reacts with the available sodium hydrogen carbonate until it is exhausted. The carbon dioxide formed is collected quantitatively.

What were the initial amounts of sodium carbonate and sodium hydrogen carbonate, respectively, and the original mixture mass? (Atomic masses: Na = 23, H = 1, C = 12, O = 16)

9. Two samples of pure hydrogen chloride are prepared using different isotopic compositions of chlorine. Sample P contains only molecules, while Sample Q contains only molecules. All hydrogen atoms are protium.
Consider the following Assertion and Reason.
Assertion: The mass percentage of chlorine in Sample Q is different from that in Sample P, although both samples have the same elemental molecular formula, HCl.
Reason: Isotopic substitution changes the mass contributed by chlorine atoms without changing the number of hydrogen and chlorine atoms in each molecule.

10. Nitrogen monoxide, NO, and urea, , are different molecular compounds. Two pure samples are prepared so that they contain equal masses of nitrogen. What are the ratio of the sample masses, NO:urea, and the ratio of their numbers of molecules? (Atomic masses: C = 12, H = 1, N = 14, O = 16)

11. A sample of pure calcium carbide reacts with water according to

The acetylene produced is burnt completely:

In the first reaction, 6.4 g of calcium carbide is treated with of water, and reaction proceeds until the limiting reagent is consumed. All acetylene obtained is transferred without loss to excess oxygen.
What are the mass of calcium hydroxide formed in the first stage and the amount of carbon dioxide formed in the second? (Atomic masses: Ca = 40, C = 12, H = 1, O = 16)

12. In a pure sample of ammonium sulphate, , the nitrogen mass percentage is compared with the percentage of nitrogen atoms among all constituent atoms represented by its formula unit. Which pair is correct? (Atomic masses: N = 14, H = 1, S = 32, O = 16)

13. A mixture contains only sodium carbonate and sodium hydrogen carbonate. The total amount of their formula units is . Exactly of HCl is supplied, and both carbonates react completely according to


No HCl remains, and no other reaction occurs. What was the mole fraction of sodium carbonate in the initial solid mixture, and what mass of sodium chloride formed? (Atomic masses: Na = 23, Cl = 35.5)

14. A pure crystalline sample has the formula . What are the percentage by mass of all oxygen present in the hydrated compound and the percentage by mass contributed specifically by oxygen atoms belonging to its water of crystallisation? (Atomic masses: Mg = 24, S = 32, O = 16, H = 1)

15. A pure sample of an element Y consists of isotopes with masses and . Its average atomic mass is . The element forms an oxide with formula . If a second sample of Y contains 75% of the isotope by number, which statement correctly compares the molar masses of prepared from the two samples? (Atomic mass of O = )

16. A mixture of carbon monoxide and carbon dioxide is passed through an apparatus in two stages.
In Stage I, the mixture is passed through excess aqueous potassium hydroxide, which completely absorbs carbon dioxide without absorbing carbon monoxide.
In Stage II, the remaining CO is burnt completely in sufficient oxygen:

The newly formed carbon dioxide is collected quantitatively.
Initially, the gas mixture weighs 14.4 g. The Stage II carbon dioxide weighs 8.8 g.
What were the initial mole fraction of CO and the mass of carbon dioxide removed in Stage I? (Atomic masses: C = 12, O = 16)

17. Two separate gaseous samples contain only molecules and molecules, respectively. The samples are chosen so that the total number of hydrogen atoms is identical in both. What is the ratio of the number of molecules in the first sample to that in the second sample, and how do their total carbon-atom counts compare?

18. Hydrogen burns in oxygen according to

Two experiments use 4.0 L hydrogen and 2.0 L oxygen at the same initial temperature and pressure, and both reactions proceed completely. In Experiment P, the product water is measured as vapour at a specified reference temperature and pressure. In Experiment Q, the product water is cooled until it becomes liquid. Which conclusion is valid?

19. A student is determining the empirical formula of a pure compound containing carbon, hydrogen and oxygen. Elemental analysis gives 40.00% carbon, 6.67% hydrogen and 53.33% oxygen by mass. The student proposes the following sequence of operations.
P. Convert the normalised atomic amounts into their simplest whole-number ratio.
Q. Treat the elemental percentages as masses in a hypothetical 100 g sample.
R. Divide each elemental mass by the corresponding atomic molar mass.
S. Divide the resulting atomic amounts by the smallest suitable nonzero amount.
Which sequence is chemically correct, and what empirical formula should it produce? (Atomic masses: C = 12, H = 1, O = 16; percentages are rounded)

20. Calcium oxide containing only oxygen-16 atoms is converted completely into calcium hydroxide using water in which 60% of the oxygen atoms are oxygen-18 and the remaining 40% are oxygen-16:

Assume that no oxygen-isotope exchange occurs other than incorporation according to the displayed reaction, and that all calcium oxide reacts. What percentage of the oxygen atoms in the resulting calcium hydroxide are oxygen-18?

21. Consider the following Assertion and Reason.
Assertion (A): Two different pure molecular compounds can have the same oxygen mass percentage and the same molar mass without having the same molecular formula.
Reason (R): The oxygen mass percentage of a compound depends on the total mass contributed by its oxygen atoms relative to its molecular mass, and different combinations of other constituent atoms may supply the same remaining mass.
Choose the correct option.

22. A pure ionic compound is formed exclusively from monatomic cations and monatomic anions . A sample of this compound contains exactly 250 constituent ions. What are the number of formula units and the number of ions in the sample?

23. A rigid, sealed vessel initially contains solid potassium chlorate and a small amount of inert argon. The potassium chlorate decomposes completely according to

The vessel is finally brought back to its original temperature. All oxygen produced remains gaseous, and no material enters or leaves the vessel.
Consider the following Assertion and Reason.
Assertion: The final total gas pressure is greater than the initial pressure, although the total mass of the sealed vessel and its contents remains unchanged.
Reason: The reaction converts oxygen atoms originally present in a solid into gaseous oxygen molecules, increasing the amount of gas without violating atom conservation.

24. A 12.4 g sample of a pure molecular compound contains only carbon, hydrogen, sulphur and oxygen. During complete combustion, all its carbon is collected as 8.8 g of , all its hydrogen as 3.6 g of , and all its sulphur as 6.4 g of . No carbon-, hydrogen- or sulphur-containing product is lost. An independent determination gives a molar mass of for the original compound. What is its molecular formula? (Atomic masses: C = 12, H = 1, S = 32, O = 16)

25. Equal amounts of hydrochloric acid are separately reacted with excess magnesium and excess aluminium:


In each experiment, exactly of HCl reacts completely. What are the ratio of metal masses consumed, magnesium:aluminium, and the ratio of hydrogen molecule counts produced in the two experiments?

26. Two pure ionic compounds, and , are taken in quantities containing equal numbers of sulphate ions. What are the respective ratios of aluminium atoms to sodium atoms and oxygen atoms in the first sample to oxygen atoms in the second sample?

27. A closed reaction system contains two different pure binary compounds of elements X and Y. Compound P contains 40% X by mass, while compound Q contains 25% X by mass. A 30 g sample of P is mixed with a 20 g sample of Q without any chemical reaction. What is the overall mass percentage of X in the resulting mixture, and does that percentage establish the formation of a new pure compound?

28. Consider the following statements about atomic mass, molecular mass, formula mass and molar mass.
Statement I: The relative atomic mass of an element is a dimensionless quantity.
Statement II: The molar mass of a substance can be expressed in or , with appropriate conversion.
Statement III: The molecular mass of a substance expressed in u and its molar mass expressed in have the same numerical value to the usual precision of chemical calculations.
Statement IV: The formula mass of sodium chloride expressed in u must equal the mass in grams of one individual NaCl formula unit.
Which statements are correct?

29. Consider the following Assertion and Reason.
Assertion (A): The law of definite proportions remains useful for identifying the composition of a pure chemical compound even though Dalton's original claim that all atoms of a given element have identical masses is not strictly correct.
Reason (R): Isotopes of an element have the same elemental identity but different masses; the ordinary fixed-composition statement must therefore be interpreted with suitable attention to isotopic composition when extremely precise mass comparisons are made.
Choose the correct option.

30. Two samples of sodium chloride have different chlorine-isotope compositions.
Sample P contains NaCl formula units. Its chlorine atoms consist of 75% chlorine-35 and 25% chlorine-37 by number.
Sample Q contains NaCl formula units, all containing chlorine-37.
The samples are combined without any chemical reaction or loss of material.
What are the average atomic mass of chlorine in the combined sample and the mass percentage of chlorine in the combined sodium chloride? (Atomic masses: Na = 23 u; chlorine isotopes = 35 u and 37 u)

31. A gaseous hydrocarbon has the general formula . At a common temperature and pressure sufficiently high to keep the product water gaseous, 20.0 mL of the hydrocarbon undergoes complete combustion with exactly 100.0 mL oxygen. The gaseous products, measured at the same reference conditions before condensation, contain 60.0 mL carbon dioxide and 80.0 mL water vapour. All oxygen is consumed. The water is subsequently condensed and removed completely, and the remaining dry gas is measured at the original reference temperature and pressure. What is the molecular formula of the hydrocarbon, and what is the final dry-gas volume?

32. A chemist prepares a gaseous mixture containing , and . At the same temperature and pressure, its molecular amount is .
Analysis gives the following:
- The combined amount of nitrogen and oxygen molecules is .
- The total amount of oxygen atoms in the mixture is .
What are the amounts of nitrogen and oxygen molecules, respectively?

33. A gaseous fuel contains only methane, , and ethane, . The total fuel amount is .
The fuel is burnt completely in sufficient oxygen:


Exactly carbon dioxide is obtained. No carbon-containing product other than carbon dioxide forms.
What are the original methane mole fraction and the total oxygen amount consumed?

34. Consider the following Assertion and Reason.
Assertion (A): Dissolving of pure sodium sulphate in water, with complete dissociation, produces of independently dispersed solute ions without changing the total number of constituent atoms originally present in the salt.
Reason (R): Every formula unit yields two sodium ions and one sulphate ion, while its constituent atoms are conserved during dissociation.
Choose the correct option.

35. A metal carbonate reacts with hydrochloric acid:

A pure sample of weighs 12.0 g and reacts completely with exactly of HCl. The resulting carbon dioxide is collected quantitatively.
Which pair gives the atomic mass of M and the volume of carbon dioxide at STP? Take . (Atomic masses: C = 12, O = 16)

36. A sample contains of pure and of pure .
Both oxides react completely with excess hydrochloric acid:


What are the total amount of HCl consumed and the total amount of dissolved chloride ions supplied by the resulting metal chlorides?

37. A sealed vessel contains two pure gases, and , in equal molecular amounts. They react completely to form HCl:

Assume constant temperature and volume, ideal-gas behaviour and no other reaction. Which statement is correct?

38. Consider the following Assertion and Reason.
Assertion (A): A molecule of water has a molecular mass of approximately , while the molar mass of water is approximately .
Reason (R): One mole contains specified entities, and the numerical conversion between atomic mass units and molar mass units makes the molecular mass in u numerically equal to the molar mass in .
Choose the correct option.

39. A hypothetical element E has an atomic molar mass of and forms two distinct gaseous molecular species, and . A uniform mixture containing only these species has an average molar mass of . What is the mole fraction of , and how many moles of E atoms are contained in 1 mol of the molecular mixture?

40. In an experiment, two different elements X and Y react according to the particle-level description below.

Which conclusion correctly evaluates this record?

41. A pure hypothetical binary compound contains only elements X and Y. Element X has atomic mass . Elemental analysis establishes that 60% of all constituent atoms are Y atoms, while Y contributes 75% of the compound's total mass. What is its empirical formula, and what is the atomic mass of Y?

42. A solution of calcium chloride is mixed with of sodium carbonate solution:

The calcium chloride solution has an unknown molarity. After complete consumption of the limiting reagent, of pure calcium carbonate precipitates, and carbonate ions remain dissolved. Assume no other reactions occur. What is the original calcium chloride molarity? (Atomic masses: Ca = 40, C = 12, O = 16)

43. Two hypothetical gaseous reactants, A and B, form gaseous C according to

In each trial, the combined initial amount of A and B is fixed at , but their individual amounts are varied. Each reaction proceeds until its limiting reagent is exhausted.

For a trial containing initially A and another trial containing initially A, which pair gives the maximum amounts of C formed, respectively?

44. A rigid vessel initially contains of nitrogen and of hydrogen. The gases react according to

At a particular stage, the total pressure is 75% of its initial value. The vessel temperature and volume remain constant, all gases behave ideally, and no other reaction occurs. What fraction of the initial nitrogen has reacted, and what is the mole fraction of ammonia in the observed mixture?

45. A 12.5 g sample of pure copper(II) sulphate pentahydrate, , is heated until all water of crystallisation has been released, without decomposition of the anhydrous sulphate. The water vapour is collected and then passed over 2.8 g of pure calcium oxide:

Assume that the calcium oxide reacts completely if sufficient water is available, and that unreacted water vapour is collected separately.
What are the mass of calcium hydroxide formed and the mass of water that remains after the calcium oxide reaction? (Atomic masses: Cu = 63.5, S = 32, O = 16, H = 1, Ca = 40)

46. A laboratory receives three colourless liquid samples P, Q and R. Each is reported to contain only hydrogen and oxygen.

P and Q are independently confirmed to be pure samples of the same compound. R is a homogeneous liquid, but its purity has not been established. Which conclusion is justified by the data?

47. Four chemical transformations are given.

For each reaction, consider the change in the total amount of gaseous molecules when the reaction proceeds by one stoichiometric reaction unit. All states are exactly as shown.
Which matching is correct?

48. Calcium carbonate reacts with hydrochloric acid according to

An experiment begins with exactly 10.0 g of pure calcium carbonate. Different amounts of HCl are supplied in separate trials, and the limiting reactant is completely consumed in each trial.

What does the graph's change in slope represent, and what mass of calcium carbonate remains when of HCl is supplied? (Atomic masses: Ca = 40, C = 12, O = 16)

49. A homogeneous gaseous mixture initially contains of and of . Exactly half the mixture is withdrawn in such a way that each component loses half its original molecular amount. Subsequently, of helium atoms is added to the remaining gas without chemical reaction. What is the total amount of constituent atoms in the final gas mixture, and what fraction of those atoms are hydrogen atoms?

50. A pure gaseous compound X has a measured molar mass of . Four candidate molecular formulae are proposed: , , and . Additional elemental analysis establishes that exactly two oxygen atoms occur in every molecule of X. Which molecular formula is consistent with all the information? (Atomic masses: C = 12, H = 1, N = 14, O = 16)