Some Basic Concepts in Chemistry Mock Test – NEET Chemistry

1. A graph is constructed for complete dissociation of calcium chloride into its constituent ions. The horizontal axis gives the amount of formula units dissolved, in moles. Two different vertical-axis quantities are considered.

What are the slopes of P and Q, respectively?

2. 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.

3. A hypothetical element X has an atomic mass of , while oxygen has an atomic mass of . A pure oxide P has the formula XO. In a separate experiment, 12 g of elemental X reacts completely with oxygen to form 28 g of a second pure oxide Q containing only X and oxygen. What is the simplest formula of Q, and what is the ratio of oxygen masses combining with the same mass of X in P and Q?

4. A 50.0 g moist sample consists exclusively of elemental metal M and physically retained water. The sample initially contains 5.0 g of water. On heating in air, all the water escapes and the entire metal portion combines with oxygen to form a single pure oxide. The final dry oxide weighs 57.0 g. What are the percentage by mass of oxygen in the final oxide and the mass of atmospheric oxygen incorporated?

5. A non-reacting gaseous mixture contains only water vapour and methane. Exactly of gas molecules is present. The total amount of constituent atoms is measured as . What are the mole fraction of methane and the average molar mass of the gas mixture? (Atomic masses: C = 12, H = 1, O = 16)

6. A uniform gaseous mixture contains exactly 4 isolated helium atoms, 3 molecules of and 2 molecules of . No other particles are present. Which set correctly gives the total number of molecules, the total number of constituent atoms and the number of chemically distinct substances in the mixture?

7. A molecular compound contains only carbon, hydrogen and nitrogen. A sample contains carbon atoms, hydrogen atoms and nitrogen atoms.
An independent measurement gives the compound a molar mass of .
What is its molecular formula, and what percentage of its molecular mass is contributed by nitrogen? (Atomic masses: C = 12, H = 1, N = 14)

8. Two hypothetical gaseous elements X and Y occur as diatomic molecules and .
At the same temperature and pressure, 2.0 L of combines completely with 1.0 L of to produce exactly 2.0 L of one gaseous compound Z, with no other products.
An independent density measurement shows that Z has 2.50 times the density of at the same temperature and pressure.
What are the molecular formula of Z and the ratio of atomic masses ?

9. A gaseous reaction occurs according to

Three identical rigid vessels contain different initial mixtures, and all reactions proceed until the limiting reagent is consumed. Temperatures are the same initially and finally. The amounts are given below.

Which sequence correctly ranks the vessels by increasing ratio of final pressure to initial pressure?

10. Iron(II) carbonate undergoes decomposition:

The FeO produced is then completely oxidised in air:

Initially, 11.6 g of pure iron(II) carbonate is used, and both stages occur completely without loss of solid material.
What are the final mass of iron(III) oxide and the net decrease in mass of material retained in the solid phase relative to the original carbonate? (Atomic masses: Fe = 56, C = 12, O = 16)

11. An ideal gaseous mixture contains only and . The total amount of gas molecules is . The mixture contains of oxygen atoms. What are the nitrogen gas mole fraction and the average molar mass of the mixture? (Atomic masses: N = 14, O = 16)

12. Consider the ionic compounds ammonium sulphate, , and ammonium nitrate, . Two pure samples are selected so that they contain equal numbers of nitrogen atoms. What is the ratio of their masses, ammonium sulphate to ammonium nitrate? (Atomic masses: H = 1, N = 14, O = 16, S = 32)

13. Two gases P and Q consist of identical diatomic molecules of the same element X, but their isotopic compositions differ. Each gas sample contains exactly of molecules. In P, every X atom has mass . In Q, every X atom has mass .
The two samples are measured at the same temperature and pressure. Which statement is correct?

14. A sample of pure sodium carbonate decahydrate, , is heated until exactly half the original water of crystallisation has escaped, while the remaining solid contains all the original sodium carbonate and retained water. Assume no other decomposition or material loss. What is the formula of the remaining hydrate, expressed per sodium carbonate formula unit, and what percentage of the original sample mass remains as solid? (Atomic masses: Na = 23, C = 12, O = 16, H = 1)

15. Potassium chlorate undergoes complete decomposition according to

A pure sample decomposes to produce 48.0 g of oxygen gas. What mass of potassium chloride is formed, and what was the original potassium chlorate mass? (Atomic masses: K = 39, Cl = 35.5, O = 16)

16. A non-reacting gaseous mixture contains only CO and . Elemental analysis establishes that oxygen contributes exactly 64% of the mixture's total mass. What are the mole fraction of and the fraction of all constituent atoms that are oxygen atoms? (Atomic masses: C = 12, O = 16)

17. A 5.10 g alloy contains only magnesium and aluminium. One sample of this alloy reacts completely with excess dilute hydrochloric acid:


Exactly hydrogen is collected.
A separate, identical 5.10 g alloy sample is burnt completely in sufficient oxygen to form only MgO and , with all solid products retained.
What are the mass percentage of magnesium in the alloy and the total mass of oxides formed from the second sample? (Atomic masses: Mg = 24, Al = 27, O = 16)

18. A graphical representation is made for a pure sample of a hypothetical diatomic gas .

What are the atomic molar mass of X and the amount of molecules present in a 12 g sample?

19. A student investigates the reaction

All gases behave ideally. Three observations are made:
Statement I: In a rigid closed vessel at constant temperature, formation of one mole of C reduces the total gaseous amount by .
Statement II: At constant temperature and pressure, complete reaction of 4.0 L A with 2.0 L B produces 4.0 L C.
Statement III: If the reaction produces a lower total gaseous amount, the total mass of a closed reacting system must decrease.
Statement IV: Adding an inert gas to a rigid vessel at fixed temperature can change the total pressure without changing the stoichiometric limiting reagent.
Which statements are correct?

20. A student prepares three separate samples: P contains of oxygen atoms, Q contains of molecules, and R contains of oxide ions, . Consider the following statements.
Statement I: P, Q and R contain equal numbers of the elementary entities explicitly specified for each sample.
Statement II: P, Q and R contain equal total numbers of oxygen atoms.
Statement III: Q contains twice as many oxygen atoms as either P or R.
Statement IV: The amount of substance represented by one mole depends on whether the specified entity is an atom, molecule or ion.
Which statements are correct?

21. Two hypothetical pure gaseous substances have molecular formulae and . Measurements of their amounts against their respective sample masses give the following graphs.

What are the ratio of their molar masses, , and the ratio of sample masses required to contain equal total numbers of constituent atoms?

22. Three separate containers contain helium gas, nitrogen gas and ammonia gas, respectively. The gases occupy equal volumes at the same temperature and pressure, and Avogadro's law is applicable. Which relationship correctly compares the total numbers of constituent atoms present in the three containers?

23. A pure hypothetical oxide has empirical formula , where X has atomic mass . Oxygen occurs as two isotopes of masses and . The isotope mixture in the oxide produces an average oxygen mass percentage of , rounded to two decimal places. Assume that these are the only oxygen isotopes present and that the elemental formula is unchanged. What percentage of oxygen atoms belong to the heavier isotope, and what is the average formula mass of the oxide?

24. 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?

25. Hydrogen and oxygen are mixed at 300 K and 1 atm. At these initial conditions, hydrogen occupies 4.0 L and oxygen occupies 3.0 L.
The gases react according to

The reaction proceeds until the limiting reagent is exhausted.
The final gases are maintained at 600 K and 1 atm, where all the product water remains as vapour. Assume ideal-gas behaviour, no gas loss and no other reaction.
What are the final total gas volume and the volume fraction of water vapour?

26. Two pure samples contain methane, , and ammonia, , respectively. Their masses are adjusted so that the total number of hydrogen atoms is identical in both samples. What is the ratio of the methane sample mass to the ammonia sample mass, and what is the ratio of their molecular counts? (Atomic masses: C = 12, N = 14, H = 1)

27. A 14.0 g solid mixture contains only copper(II) oxide, CuO, and copper(I) oxide, . The mixture is completely reduced to elemental copper using excess hydrogen:


The recovered copper weighs exactly 12.0 g.
What were the original mass of and the total amount of hydrogen consumed? (Atomic masses: Cu = 64, O = 16)

28. Elemental carbon is reacted with oxygen in two separate experiments. Carbon is present in excess in both experiments, and exactly of oxygen gas is completely consumed in each.
In Experiment P, the only product is carbon monoxide:

In Experiment Q, the only product is carbon dioxide:

What are the ratios of the gaseous product masses and the amounts of carbon consumed ? (Atomic masses: C = 12, O = 16)

29. 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?

30. A closed reaction vessel initially contains 50 g of a pure compound A and 30 g of a pure compound B. The reaction produces only three substances: solid P, liquid Q and gaseous R. After reaction, all the gas is transferred completely to a separate closed container without loss. The measured masses of P and Q are 24 g and 41 g, respectively. The transferred gas is then divided into two portions having masses in the ratio . What is the mass of the larger gaseous portion?

31. A closed container initially contains of pure water vapour. The container is cooled until exactly two-thirds of the water molecules become liquid, while the remaining one-third stay in the vapour phase. No water enters or leaves, and no chemical reaction occurs. Which pair correctly gives the total amount of water molecules in both phases combined and the amount of oxygen atoms remaining specifically in the vapour phase?

32. 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?

33. Ammonium phosphate reacts with calcium hydroxide according to the skeletal equation

Initially, of ammonium phosphate is supplied with of calcium hydroxide. The reaction proceeds until the limiting reagent is consumed, and no other reaction occurs.
What are the amount of ammonia produced and the amount of unreacted ammonium phosphate?

34. The total mass of a pure iron oxide is plotted against the mass of oxygen chemically combined in it.

What is the empirical formula of the oxide? (Atomic masses: Fe = 56, O = 16)

35. Calcium phosphate reacts with sulphuric acid according to

Assume that these are the only products and that the reaction proceeds until the limiting reagent is consumed. Initially, of calcium phosphate and of sulphuric acid are supplied. What are the amount of phosphoric acid produced and the amount of calcium phosphate remaining?

36. Nitrogen and hydrogen react to form ammonia according to

All gaseous volumes are compared at the same temperature and pressure. Using atomic masses and , which pair correctly gives the ratio of reacting gas volumes and the ratio of their reacting masses ?

37. 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)

38. A researcher investigates the reaction

An experiment starts with known amounts of A and B, but it is not established whether the reaction reached completion. A measured amount of C is available. Which additional information is sufficient to distinguish the actual amount of A consumed from its original amount and determine the fraction of initial A that reacted?

39. A 50 g sample of limestone contains only calcium carbonate and an inert, non-volatile impurity. On heating, part of the calcium carbonate decomposes according to

The sample loses 8.8 g in mass due entirely to escaping carbon dioxide. The unreacted calcium carbonate is subsequently separated and found to weigh 10 g. What was the percentage purity of calcium carbonate in the original limestone? (Atomic masses: Ca = 40, C = 12, O = 16)

40. A reaction is described by

where X and Y are hypothetical elements. The reaction takes place in a closed vessel and proceeds completely according to the equation. Consider the following statements.
Statement I: The equation conserves both X atoms and Y atoms.
Statement II: For every five reactant molecules consumed, two product molecules are formed.
Statement III: The number of gaseous molecules decreases, so the total gas mass must also decrease.
Statement IV: At a common temperature and pressure, the total volume of the reacting gaseous reactants is five times the volume corresponding to one gaseous molecular quantity, whereas the product volume corresponds to two such quantities.
Which statements are correct?

41. A gaseous sample contains only molecules of two hypothetical compounds, and . Both molecular species are stable under the stated conditions. The sample contains exactly 12 X atoms, 24 Y atoms and 9 molecules in total. What is the number of molecules of each compound?

42. A sample is prepared by dissolving sugar completely in water. The resulting liquid has the same composition throughout. How should this sample be classified?

43. Excess zinc is reacted with hydrochloric acid inside a vessel that initially contains of chemically inert nitrogen gas:

The reaction proceeds until all supplied HCl has reacted. After the reaction, the dry gas mixture contains only nitrogen and hydrogen, and hydrogen has a mole fraction of . What amount of HCl was initially supplied, and what mass of zinc reacted? (Atomic mass: Zn = 65)

44. A rigid vessel initially contains of CO, of oxygen and of inert nitrogen. Carbon monoxide reacts completely to form carbon dioxide:

The temperature and volume remain constant, all gases behave ideally, and no other reaction occurs. What are the ratio of final to initial pressure and the fraction of all final constituent atoms that are oxygen atoms?

45. An oxide mixture contains only pure MgO and pure . Its mass is 9.10 g. The oxides are completely consumed by hydrochloric acid:


Exactly HCl is consumed. No other reaction occurs.
What was the original mass percentage of MgO, and what mass of water is formed? (Atomic masses: Mg = 24, Al = 27, O = 16, H = 1)

46. Four claims are made about experimental evidence for the laws of chemical combination.
Statement I: A closed reaction system may conserve its total mass even when the total number of gaseous molecules changes.
Statement II: A simple whole-number ratio between two measured masses is sufficient by itself to establish the law of multiple proportions.
Statement III: Equal volumes of different gases at the same temperature and pressure contain equal numbers of molecules, but their total constituent-atom counts need not be equal.
Statement IV: The law of definite proportions requires different samples of the same pure compound to contain equal absolute masses of each constituent element.
Which combination contains only the correct statements?

47. 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)

48. A pure gaseous mixture contains hydrogen and carbon monoxide. At a given temperature and pressure, 10.0 L of the mixture weighs 6.0 g. At the same temperature and pressure, 10.0 L of pure nitrogen gas weighs 10.0 g.
Assume ideal-gas behaviour and no reaction during measurement. What are the mole fraction of hydrogen and the average molar mass of the original gas mixture? (Atomic masses: H = 1, C = 12, N = 14, O = 16)

49. Four experiments are performed to prepare the same pure binary compound Z from elements X and Y. In every experiment, the stated mass of X is consumed completely, and only Z and possibly some unreacted Y remain.

Which conclusion follows from conservation of mass and definite proportions?

50. At the same temperature and pressure, two gaseous elements X and Y react completely to form a single gaseous compound Z.
An experiment establishes that 2.0 L of X reacts with 3.0 L of Y to produce 2.0 L of Z.
Independent information shows that the reacting elemental molecules are and .
Which molecular formula for Z is consistent with both the gaseous volume observations and atom conservation?