Quick recall · 69 cards
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Number of atoms in the following samples of substances is the largest in:
(a) 16 g of O₃
(b) 28 g of CO
(c) 32 g of O₂
(d) 36 g of H₂O
D · 36 g of H₂O
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The ratio of mass percent of C and H of an organic compound (CₓHᵧO₂) is 6:1. If the compound contains 40% oxygen by mass then the empirical formula of the compound is:
(a) CH₂O
(b) CH₂O₂
(c) C₆H₆O₂
(d) C₃H₅O
D · C₃H₅O
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Given vapour density = 94.8 and 74.75% chlorine by mass, identify the formula from: (1) MCl₄ (2) MCl₂ (3) MCl₅ (4) MCl₃
A · MCl₄
PYQ · 2019
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Which law states that mass can neither be created nor destroyed in a chemical reaction?
A. Law of Definite Proportions
B. Law of Multiple Proportions
C. Law of Conservation of Mass
D. Avogadro’s Law
C · Law of Conservation of Mass
PYQ · 2019
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Which of the following sets of compounds illustrates the **law of multiple proportions**?
A. N₂O₃, N₂O₄, N₂O₅
B. NaCl, NaBr, NaI
C. CS₂, CO₂, SO₂
D. PH₃, P₂O₃, P₂O₅
A · N₂O₃, N₂O₄, N₂O₅
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Mole fraction of solvent in 0.2 m binary aqueous solution of camphor (m = molality)
(A) 0.996
(B) 0.004
(C) 0.96
(D) 0.976
A · 0.996
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Which of the following best states the law of conservation of mass?
A · Mass is neither created nor destroyed in a chemical reaction
The law of conservation of mass states that mass remains constant during a chemical reaction; it is neither created nor destroyed.
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In a closed system, during a chemical reaction, the total mass of reactants and products is:
A · Equal
According to the law of conservation of mass, the total mass of reactants equals the total mass of products in a closed system.
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Refer to the diagram below showing a chemical reaction in a closed container.
If the mass of reactants is 50 g, what will be the mass of products after the reaction?
A · 50 g
The law of conservation of mass ensures that mass remains constant; hence, the mass of products equals the mass of reactants (50 g).
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If 12 g of carbon reacts completely with 32 g of oxygen to form carbon dioxide, the total mass of carbon dioxide formed is:
A · 44 g
According to the law of conservation of mass, total mass of products = total mass of reactants = 12 g + 32 g = 44 g.
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Which statement correctly describes the law of definite proportions?
A · A chemical compound always contains the same elements in the same proportion by mass
The law of definite proportions states that a chemical compound contains the same elements in a fixed proportion by mass regardless of the source or amount.
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An unknown compound contains 40% carbon and 6.7% hydrogen by mass. The remaining mass is oxygen. According to the law of definite proportions, which of the following is true?
A · The ratio of elements by mass in the compound is fixed
The law of definite proportions states that a pure compound always contains elements in a fixed mass ratio.
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Refer to the table below showing mass percentages of elements in three samples of a compound.
Which law is demonstrated by the constant mass ratios in the samples?
A · Law of definite proportions
The constant mass ratios of elements in different samples of the same compound illustrate the law of definite proportions.
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If a compound contains 24 g of carbon and 32 g of oxygen, what is the mass ratio of carbon to oxygen according to the law of definite proportions?
A · 3:4
Mass ratio of carbon to oxygen = 24 g : 32 g = 3 : 4, consistent with the law of definite proportions.
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A compound contains 54.5% silver and 45.5% chlorine by mass. Another compound contains 75.8% silver and 24.2% chlorine. Which law explains the relationship between these compounds?
A · Law of multiple proportions
The law of multiple proportions explains that when two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in simple whole number ratios.
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Which of the following is an example of the law of multiple proportions?
A · CO and CO₂
CO and CO₂ are two compounds of carbon and oxygen where the masses of oxygen that combine with a fixed mass of carbon are in simple whole number ratios, illustrating the law of multiple proportions.
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Two compounds contain elements A and B. In compound 1, 10 g of A combines with 15 g of B. In compound 2, 10 g of A combines with 30 g of B. What is the ratio of masses of B that combine with a fixed mass of A?
A · 1:2
Mass ratio of B = 15 g : 30 g = 1 : 2, which is a simple whole number ratio illustrating the law of multiple proportions.
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Refer to the graph below showing masses of element B combining with a fixed mass of element A in two compounds.
What does this graph illustrate?
A · Law of multiple proportions
The graph shows that the masses of element B combining with a fixed mass of A are in simple whole number ratios, illustrating the law of multiple proportions.
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Given that 12 g of carbon combines with 16 g of oxygen to form CO, and 12 g of carbon combines with 32 g of oxygen to form CO₂, what is the ratio of masses of oxygen that combine with a fixed mass of carbon?
A · 1:2
The masses of oxygen combining with 12 g carbon are 16 g and 32 g, ratio 16:32 = 1:2, illustrating the law of multiple proportions.
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Two compounds X and Y contain elements P and Q. Compound X has 5 g of P combined with 10 g of Q. Compound Y has 5 g of P combined with 15 g of Q. Which law is demonstrated by these compounds?
A · Law of multiple proportions
The masses of Q combining with fixed mass of P are in simple whole number ratios (10:15 = 2:3), illustrating the law of multiple proportions.
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Which law is illustrated by the statement: "When two elements combine to form more than one compound, the masses of one element that combine with a fixed mass of the other are in ratios of small whole numbers"?
A · Law of multiple proportions
This statement is the definition of the law of multiple proportions.
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Which of the following best states the law of conservation of mass?
A · Mass of reactants equals mass of products in a chemical reaction
The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction, so the total mass of reactants equals the total mass of products.
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According to the law of definite proportions, a chemical compound always contains:
A · Elements in the same mass ratio regardless of source
The law of definite proportions states that a chemical compound contains the same elements in exactly the same proportion by mass regardless of the amount or source of the compound.
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In a chemical reaction, 10 g of reactant A combines with 15 g of reactant B to form a product. According to the law of conservation of mass, the mass of the product formed is:
A · 25 g
According to the law of conservation of mass, total mass of reactants equals total mass of products, so product mass = 10 g + 15 g = 25 g.
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Refer to the diagram below showing a reaction where mass is measured before and after reaction.
What does the graph indicate about the total mass during the reaction?
A · Mass remains constant throughout the reaction
The graph shows a horizontal line indicating mass remains constant during the reaction, illustrating the law of conservation of mass.
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If 24 g of carbon combines with 32 g of oxygen to form carbon dioxide, what is the mass ratio of carbon to oxygen in the compound?
A · 3:4
Mass ratio of C to O = 24 g : 32 g = 3 : 4, consistent with the law of definite proportions.
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Which of the following compounds violates the law of definite proportions?
A · A compound with varying mass ratios of elements in different samples
A compound with varying mass ratios of elements in different samples violates the law of definite proportions, which requires fixed mass ratios.
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Two compounds are formed by elements A and B. In compound 1, 10 g of A combines with 20 g of B. In compound 2, 10 g of A combines with 30 g of B. What is the ratio of masses of B that combine with fixed mass of A?
A · 2:3
Ratio of masses of B = 20 g : 30 g = 2 : 3, a simple whole number ratio illustrating the law of multiple proportions.
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Refer to the reaction scheme below showing two compounds formed by elements X and Y.
Compound 1: X₂Y
Compound 2: XY
What is the ratio of masses of element Y that combine with a fixed mass of element X?
A · 1:0.5
In X₂Y, mass of Y per X atom is half that in XY, so ratio is 1:0.5, consistent with law of multiple proportions.
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Which of the following examples illustrates the law of conservation of mass during a chemical reaction?
A · Burning of magnesium ribbon in air where mass of magnesium oxide formed equals mass of magnesium plus oxygen consumed
In burning magnesium, the total mass of magnesium and oxygen equals the mass of magnesium oxide formed, illustrating conservation of mass.
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If 5 g of hydrogen combines with 40 g of oxygen to form water, what is the mass percent of hydrogen in water?
A · 11.11%
Mass percent of H = (5 / (5+40)) \times 100 = 11.11%.
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Two compounds contain the same elements P and Q. In compound 1, 4 g of P combines with 6 g of Q. In compound 2, 4 g of P combines with 9 g of Q. What is the ratio of masses of Q that combine with fixed mass of P?
A · 2:3
Ratio of Q masses = 6 g : 9 g = 2 : 3, a simple whole number ratio illustrating law of multiple proportions.
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Which of the following is an example of the law of definite proportions?
A · Water always contains hydrogen and oxygen in 2:16 mass ratio
Water always contains hydrogen and oxygen in a fixed mass ratio (2:16), illustrating the law of definite proportions.
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Refer to the reaction scheme below for two compounds formed by elements M and N:
Compound 1: MNO
Compound 2: MNO₂
What does this illustrate about the masses of N combining with fixed mass of M?
A · Mass of N in compound 2 is twice that in compound 1
Compound 2 has twice the number of oxygen atoms as compound 1, so mass of N combining with fixed M doubles, illustrating law of multiple proportions.
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In a reaction, 14 g of nitrogen reacts with 48 g of oxygen to form nitrogen dioxide. What is the mass ratio of nitrogen to oxygen in nitrogen dioxide?
A · 7:24
Mass ratio N:O = 14 g : 48 g = 7 : 24, consistent with law of definite proportions.
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What is the correct definition of molarity?
A · Number of moles of solute per litre of solution
Molarity is defined as the number of moles of solute dissolved in one litre of solution.
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Molarity of a solution is expressed in which units?
A · mol/L
Molarity is expressed as moles of solute per litre of solution, so its unit is mol/L.
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Which of the following best defines molality?
A · Moles of solute per kilogram of solvent
Molality is defined as the number of moles of solute dissolved in one kilogram of solvent.
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The unit of molality is:
A · mol/kg
Molality is expressed as moles of solute per kilogram of solvent, so its unit is mol/kg.
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Which statement correctly distinguishes molarity from molality?
A · Molarity depends on volume of solution; molality depends on mass of solvent
Molarity is based on volume of solution, which can change with temperature, while molality is based on mass of solvent, which is temperature independent.
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Which of the following is NOT a difference between molarity and molality?
C · Molarity is used for solids; molality is used for gases
Both molarity and molality can be used for solutions of solids, liquids, or gases; the statement that molarity is used for solids and molality for gases is incorrect.
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Why does molarity change with temperature while molality remains constant?
A · Because volume changes with temperature but mass does not
Volume expands or contracts with temperature changes affecting molarity, but mass remains constant, so molality is unaffected.
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Which of the following formulas correctly calculates molarity (M)?
A · \( M = \frac{\text{moles of solute}}{\text{volume of solution in litres}} \)
Molarity is defined as moles of solute divided by volume of solution in litres.
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Calculate the molarity of a solution prepared by dissolving 0.5 moles of NaCl in 2 litres of solution.
A · 0.25 mol/L
Molarity \( M = \frac{0.5}{2} = 0.25 \) mol/L.
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A solution contains 40 g of glucose (molar mass = 180 g/mol) dissolved in 500 mL of solution. What is its molarity?
A · 0.44 mol/L
Moles of glucose = \( \frac{40}{180} = 0.222 \) molVolume = 0.5 LMolarity = \( \frac{0.222}{0.5} = 0.444 \) mol/L (closest option is 0.44 mol/L).
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Which of the following is the correct formula for molality (m)?
A · \( m = \frac{\text{moles of solute}}{\text{mass of solvent in kg}} \)
Molality is defined as moles of solute per kilogram of solvent.
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Calculate the molality of a solution prepared by dissolving 1 mole of KCl in 2 kg of water.
A · 0.5 mol/kg
Molality \( m = \frac{1}{2} = 0.5 \) mol/kg.
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A solution contains 58.5 g of NaCl (molar mass = 58.5 g/mol) dissolved in 1 kg of water. What is its molality?
A · 1 mol/kg
Moles of NaCl = \( \frac{58.5}{58.5} = 1 \) molMass of solvent = 1 kgMolality = 1 mol/kg.
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Which concentration term remains unaffected by temperature changes?
A · Molality
Molality depends on mass of solvent which does not change with temperature, so it remains constant.
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Refer to the diagram below showing how molarity changes with temperature while molality remains constant. Which curve represents molality?
A · The horizontal line
Molality remains constant with temperature, so it is represented by the horizontal line; molarity changes due to volume expansion/contraction.
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Which of the following best defines the concept of solution concentration?
A · Amount of solute present per unit amount of solution
Solution concentration refers to the amount of solute present in a given quantity of solution.
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Which of the following concentration terms is independent of the total volume of solution?
A · Molality
Molality depends on mass of solvent, not on solution volume, so it is independent of volume changes.
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Refer to the schematic diagram below of a solution concentration setup. Which component represents the solvent?
A · The larger container holding the liquid
The solvent is the major component, usually the liquid in the larger container where solute is dissolved.
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Given density of solution is 1.2 g/mL, molality is 2 mol/kg, and molar mass of solute is 60 g/mol, calculate the molarity of the solution.
A · 2.4 mol/L
Using the relation \( M = \frac{m \times d}{1 + m \times M_w} = \frac{2 \times 1.2}{1 + 2 \times 0.06} = \frac{2.4}{1.12} \approx 2.14 \) mol/L (closest option 2.4 mol/L).
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Which of the following formulas correctly relates molarity (M) and molality (m) given density \( d \) of solution and molar mass \( M_w \) of solute?
A · \( M = \frac{m \times d}{1 + m \times M_w} \)
The correct interconversion formula is \( M = \frac{m \times d}{1 + m \times M_w} \), where \( d \) is density of solution and \( M_w \) is molar mass of solute.
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Calculate the molality of a solution if its molarity is 3 mol/L, density is 1.2 g/mL, and molar mass of solute is 60 g/mol.
A · 2.8 mol/kg
Using \( m = \frac{M}{d - M \times M_w} = \frac{3}{1.2 - 3 \times 0.06} = \frac{3}{1.2 - 0.18} = \frac{3}{1.02} \approx 2.94 \) mol/kg (closest option 2.8 mol/kg).
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Which practical application uses molarity as the preferred concentration term?
A · Preparing standard solutions in volumetric analysis
Molarity is commonly used in volumetric analysis because volume measurement is easier and more practical in titrations.
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Molality is preferred over molarity in which of the following applications?
A · Studying temperature-dependent colligative properties
Molality is temperature independent and preferred for colligative property studies where temperature varies.
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A solution is prepared by dissolving 10 g of solute (molar mass 50 g/mol) in 500 g of solvent. Its molality is 0.4 mol/kg. Calculate the molarity if the solution density is 1.2 g/mL.
B · 0.48 mol/L
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A solution is made by mixing 300 mL of 2.5 M HCl with 200 g of water. The density of the final solution is 1.1 g/mL. What is the molality of HCl in the final solution?
C · Approximately 1.5 m
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A solution is prepared by dissolving 0.2 mol of a solute in 100 g of solvent. The density of the solution is 1.1 g/mL, and the total volume is 190 mL. Which of the following statements is correct?
A · Molarity is approximately 1.05 M, molality is 2.0 m, molality > molarity
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A solution contains 0.1 mol of solute dissolved in 50 g of solvent. The density of the solution is 1.2 g/mL and the total volume is 80 mL. Calculate molarity and molality and identify the correct statement.
A · Molarity ≈ 1.25 M, Molality ≈ 2.0 m, Molarity < Molality
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A solution is prepared by dissolving 10 g of NaOH (molar mass = 40 g/mol) in 250 g of water. The density of the solution is 1.05 g/mL. Calculate molarity and molality and determine which is true.
C · Molarity ≈ 0.95 M, Molality ≈ 1.0 m, Molarity < Molality
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A solution is prepared by mixing 100 mL of 3 M NaCl solution with 100 g of water. The density of the final solution is 1.1 g/mL. Calculate the molality of NaCl in the final solution.
C · Approximately 1.5 m
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A solution contains 0.4 mol of solute dissolved in 400 g of solvent. The density of the solution is 1.08 g/mL and total volume is 420 mL. Which statement is correct?
A · Molarity ≈ 0.95 M, Molality ≈ 1.0 m, Molarity < Molality
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A solution is prepared by dissolving 15 g of a solute (molar mass = 75 g/mol) in 350 g of water. The density of the solution is 1.03 g/mL. Calculate molarity and molality and identify the correct relationship.
B · Molarity ≈ 0.57 M, Molality ≈ 0.6 m, Molality > Molarity
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A solution is prepared by dissolving 0.3 mol of solute in 400 g of solvent. The density of the solution is 1.1 g/mL and the total volume is 350 mL. Which of the following is true?
A · Molarity ≈ 0.86 M, Molality ≈ 0.75 m, Molarity > Molality
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A solution is prepared by dissolving 0.25 mol of solute in 300 g of solvent. The density of the solution is 1.15 g/mL and the volume is 260 mL. Which statement is correct?
A · Molarity ≈ 0.96 M, Molality ≈ 0.83 m, Molarity > Molality
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A solution is prepared by dissolving 0.1 mol of solute in 150 g of solvent. The density of the solution is 1.12 g/mL and the total volume is 120 mL. Which of the following is true?
A · Molarity ≈ 0.83 M, Molality ≈ 0.67 m, Molarity > Molality
