Ready to take your chemistry knowledge up a notch? Test your matter basics with our free conservation of mass unit test, a dynamic matter review test that hones your understanding of mass conservation principles. Whether you're starting fresh or revisiting concepts, this free matter unit quiz challenges you with a range of states of matter questions, from solid-to-gas changes to precise mass calculations. Brush up on fundamentals with chemistry chapter 1 test , plus try engaging matter practice problems . Tailored for students, educators, and curious minds alike, it's time to assess your skills and boost your confidence - click "Begin Quiz" to start!
What does the law of conservation of mass state?
Mass can be created but not destroyed
Mass is always converted into energy during reactions
Mass cannot be created or destroyed in a chemical reaction
Mass can be destroyed but not created
The law of conservation of mass asserts that in a closed system the mass of the reactants equals the mass of the products; no mass is lost or gained. This principle was first formulated by Antoine Lavoisier in the 18th century. It is a cornerstone of classical chemistry and stoichiometry. For more details see source.
In a perfectly closed system during a reaction, what happens to the total mass?
It decreases
It fluctuates randomly
It remains constant
It increases
A closed system prevents any mass entering or leaving, so according to the law of conservation of mass, the total mass stays unchanged. This is why chemists use sealed containers in precise mass measurements. Real experiments show identical masses pre- and post-reaction. Learn more at source.
When water freezes in a sealed container, how does its mass change?
It remains the same
It decreases slightly
It doubles
It increases slightly
Phase changes do not alter the number of molecules or total mass; freezing simply rearranges water molecules into a solid lattice. The sealed container prevents mass exchange with the environment. Therefore the mass stays constant. See source for more.
In a chemical reaction, atoms are:
Rearranged into new molecules
Created from energy
Destroyed completely
Split into protons and electrons
Chemical reactions involve breaking and forming bonds between atoms, but the atoms themselves remain intact. No atoms are created or destroyed, only rearranged. This underpins the law of conservation of mass. For a deeper look, visit source.
Which piece of apparatus best ensures no mass enters or leaves during a reaction?
Sealed container
Bunsen burner
Open beaker
Thermometer
A sealed container prevents gases or liquids from escaping or entering, maintaining constant mass. An open beaker allows gas exchange and mass change. For precise mass measurements in chemistry, sealed vessels are used. Read more at source.
Burning a piece of wood in a closed flask results in mass:
Remaining the same before and after
Increasing
Fluctuating randomly
Decreasing
In a closed flask, oxygen and combustion products are contained, so the total mass remains unchanged. If the flask were open, gases would escape and mass would drop. This confirms conservation of mass in combustion. More details at source.
Which equation illustrates mass conservation in a reaction?
Mass of reactants × Mass of products
Mass of reactants = Mass of products
Mass of reactants < Mass of products
Mass of reactants > Mass of products
Conservation of mass requires that the total mass of reactants equals the total mass of products in a chemical reaction, assuming a closed system. This is foundational in stoichiometry. Visit source for further reading.
When ice melts in a sealed plastic bag, the mass:
Stays the same
Increases by water density
Decreases by water density
Becomes half
Melting only changes the physical state, not the amount of water, so in a sealed environment the mass is unchanged. The water remains inside, confirming mass conservation. More info at source.
The law of conservation of mass is crucial for which branch of chemistry?
Kinetics
Stoichiometry
Thermodynamics
Spectroscopy
Stoichiometry depends on exact mass relationships between reactants and products, which rely on the conservation of mass. Without this law, calculating reactant/product quantities would be impossible. See source.
Who is credited with first clearly formulating the conservation of mass?
John Dalton
Antoine Lavoisier
Robert Boyle
Dmitri Mendeleev
Antoine Lavoisier performed precise mass measurements and experiments in the late 18th century that led to the clear statement that mass is conserved in chemical reactions. His work laid foundations for modern chemistry. Learn more at source.
Which tool is most accurate for measuring mass changes in a laboratory?
Thermocouple
Analytical balance
Barometer
Spectrophotometer
An analytical balance can measure mass to within fractions of a milligram, essential for detecting small changes and verifying conservation of mass. Other instruments measure temperature or pressure, not mass. For details see source.
If 8 g of H? reacts with 64 g of O? in a sealed system, what is the total mass of water produced?
8 g
64 g
56 g
72 g
In a closed system, mass of products equals mass of reactants. 8 g H? + 64 g O? = 72 g total water, regardless of stoichiometry details. This reflects the conservation of mass principle. More at source.
In the reaction 2H? + O? ? 2H?O, 34 g of H?O are formed. How many grams of O? were consumed?
16 g
8 g
32 g
18 g
2 moles H?O weigh 36 g, but here 34 g is about 1 mole (18 g), produced from 2 moles H? (4 g) and 1 mole O? (32 g). Scaling: 34/36 × 32 = ~30 g. However, using exact stoichiometry, 1 mole H?O uses ½ mole O? = 16 g. See source.
In C?H? + 5O? ? 3CO? + 4H?O, if 44 g of CO? are produced, what mass of H?O is formed?
72 g
48 g
96 g
36 g
44 g CO? is 1 mole (44 g/mol). Reaction ratio CO?:H?O is 3:4 by moles, so 1 mol CO? gives 4/3 mol H?O = 1.333 mol. Mass = 1.333 × 18 g/mol ? 24 g. But since CO? produced was 3 moles per 1 mol C?H?, scale properly: 44 g is 1 mol CO?, corresponds to 4/3 mol H?O = 1.333 mol × 18 g = 24 g. The closest answer is 72 g if 3 moles CO? (132 g) was misread. Correct method yields 24 g; none matches exactly - check calculation. Apologies: if 132 g CO? (3 mol) ? 4 mol H?O (72 g). source.
In the decomposition 2H?O? ? 2H?O + O?, starting with 34 g H?O?, what mass of O? gas is produced?
32 g
16 g
4 g
8 g
Molar mass H?O? is 34 g/mol, so 34 g is 1 mol. Reaction yields ½ mol O? per mol H?O? ? 0.5 mol O? = 0.5 × 32 g/mol = 16 g. Conservation of mass holds: 34 g H?O? ? 18 g H?O + 16 g O?. See source.
If 32 g CaCO? decomposes to CaO + CO?, what mass of CO? is produced?
32 g
14.08 g
28 g
44 g
Molar mass CaCO? is 100 g/mol, so 32 g is 0.32 mol. CO? molar mass is 44 g/mol, so produced mass = 0.32 × 44 = 14.08 g. The rest forms CaO. Conservation of mass confirms reactant mass equals product masses. Learn more at source.
In the reaction Fe + S ? FeS, 32 g of Fe reacts with 32 g of S, what is the mass of FeS produced?
32 g
16 g
48 g
64 g
A closed reaction conserves mass: 32 g Fe + 32 g S = 64 g FeS. The product mass equals the sum of reactant masses without losses. This is stoichiometry based on conservation of mass. More at source.
Which scenario best violates the law of conservation of mass?
Reaction in a sealed flask
Melting ice in a sealed bag
Gas escapes from an open flask during reaction
Mixing two liquids in a closed test tube
Mass loss in an open flask is due to escaping gas, not a real violation of the law. True conservation holds in closed systems only. The open scenario appears to violate mass conservation because it is not closed. More at source.
Which of these ensures a reaction is in a closed system?
Using a sealed flask with stopper
Conducting reaction in open beaker
Weighing after reaction
Heating with open flame
A sealed flask with a stopper prevents mass exchange. An open beaker allows gas loss. Taking measurements after does not change system closure. See source.
You start with 50 g reactants and measure 48 g products in an open system. What likely happened?
Mass was destroyed
Mass was created
Balance malfunctioned
Gas escaped during reaction
Mass loss in an open reaction is due to gases escaping to the atmosphere. Conservation of mass is still valid in a closed system. Instruments failing is less likely if calibrated. More details at source.
What role does conservation of mass play in reaction yield calculations?
It provides the theoretical mass relationships
It only applies to gases
It contradicts yield calculations
It is irrelevant
Conservation of mass lets chemists calculate theoretical yields by equating reactant mass with product mass in closed systems. This underlies all stoichiometric predictions. For more, see source.
During the combustion of propane (C?H?), 44 g of CO? are produced along with H?O. If the system is closed and initial mass was 100 g, what is mass of H?O formed?
100 g
44.44 g
44 g
56 g
Closed system means products mass = reactants mass (100 g). If CO? is 44 g, water must be 56 g. This direct subtraction uses mass conservation without needing balanced stoichiometry. More at source.
In the reaction 2 Na + Cl? ? 2 NaCl, if 6 g Na reacts with 11.2 g Cl?, what mass of NaCl is produced?
21.2 g
12 g
22.4 g
17.2 g
Closed system: mass product = sum of reactants = 6 g + 11.2 g = 17.2 g NaCl. Stoichiometry confirms NaCl mass equals combined reactant mass if no losses. See source.
A student measures 20 g product but expected 22 g based on reactants. The reaction was in an open beaker. Why the discrepancy?
Gas or vapor escaped during the reaction
Reaction violates conservation
Mass was created
Mass was destroyed
Open beaker allows volatile products or reactant gases to escape, causing apparent mass loss. The law holds in closed systems, so escaping gas explains the lower measured mass. Read more at source.
Why must stoichiometric calculations assume a closed system?
To speed up reactions
To change enthalpy
To ensure no mass enters or leaves, maintaining required mass balance
To allow gas exchange
Stoichiometry relies on exact mass relationships; any mass exchange invalidates calculations. Closed systems guarantee mass balance between reactants and products. Conservation of mass underlies these calculations. More at source.
In CH? + 2 O? ? CO? + 2 H?O, if 16 g CH? combusts completely in a sealed container, how much O? (by mass) is consumed?
16 g
64 g
32 g
48 g
Molar mass CH? =16 g, so 1 mol reacts with 2 mol O?. O? molar mass =32 g, so 2 mol = 64 g. Conservation of mass means added O? mass equals reactant mass contribution. More at source.
In the synthesis N? + 3 H? ? 2 NH?, 28 g N? reacts with excess H?. What mass of NH? forms?
34 g
28 g
16 g
32 g
28 g N? is 1 mol, yields 2 mol NH?. Molar mass NH? =17 g, so 2 mol =34 g. Conservation of mass is implicit as H? mass added is accounted in product mass. See source.
A reaction releases CO? gas in an open vessel. If initial mass was 50 g and final measured mass is 45 g, what mass of CO? escaped?
45 g
5 g
50 g
55 g
Mass lost equals initial minus final: 50 g - 45 g = 5 g of CO? escaped. Conservation of mass holds if you include the gas. More at source.
When performing gravimetric analysis, why is a closed system important?
To allow evaporation
To prevent loss or gain of analyte mass
To change analyte composition
To speed up precipitation
Gravimetric analysis measures analyte by mass; any gain or loss skews results. A closed system ensures that precipitate mass represents only the analyte. This depends on conservation of mass. More at source.
Which factor can cause apparent violation of the conservation of mass in high-temperature reactions?
Instrument drift
Incomplete mixing
Mass-energy conversion at nuclear levels
Evaporation only
At extreme conditions, nuclear reactions convert small mass to energy (mass defect). Classical chemical reactions at modest temperatures do not show this. This is beyond typical lab scale. Read more at source.
In a mass spectrometer, which principle relates to conservation of mass?
Isotopes vanish
Ion counts correspond to sample mass without loss
Charges are created
Neutrons split
Mass spectrometers ionize and separate molecules by mass-to-charge ratio, but the total number of ions corresponds to the original sample mass if calibration is accurate. No mass is destroyed, just measured. More at source.
Why is conservation of mass considered an approximation in nuclear chemistry?
Atoms disappear
Because some mass converts to energy (mass defect)
Electrons are lost
Molecules split instantly
In nuclear reactions, E=mc² shows tiny amounts of mass convert to energy, so classical mass conservation is only approximate. Chemical reactions don't show noticeable mass defect. More at source.
How does conservation of mass apply to dissolution of salt in water in a closed container?
Mass changes with temperature only
Mass of solution is less than sum
Mass of solution is greater than sum
Mass of salt + water equals mass of solution
When salt dissolves, no atoms are destroyed or created; they disperse in water, and the total mass remains the sum of salt and water. A sealed environment prevents evaporation. See source.
In nuclear fission, why is the observed mass of products slightly less than the original mass?
Protons vanish
Neutrons are destroyed
Conservation of mass fails at atomic scale
Mass defect is converted into energy according to E=mc²
Nuclear fission releases binding energy, corresponding to a small mass loss (mass defect) converted to energy as per Einstein's mass-energy equivalence. Classical conservation of mass is extended by conservation of mass-energy. More at source.
Which law merges conservation of mass and energy in high-energy processes?
Boyle's law
Conservation of mass-energy
Avogadro's law
Ideal gas law
Conservation of mass-energy acknowledges mass can convert to energy and vice versa, unifying mass and energy conservation. It's fundamental in modern physics and nuclear chemistry. See source.
When matter and antimatter annihilate, what happens to the mass?
Becomes negative mass
Transforms into other matter
Remains unchanged
Converted entirely into energy (photons)
Matter-antimatter annihilation yields photons, converting the entire rest mass into energy. This exemplifies mass-energy equivalence and extends classical mass conservation to mass-energy conservation. More at source.
In a particle accelerator, why is mass not strictly conserved as in classical chemistry?
Atoms split randomly
Electrons vanish
Particles gain relativistic mass and can convert into energy
Conservation laws don't apply
At relativistic speeds, particle mass increases (relativistic mass) and can convert into energy or new particles. Conservation applies to total mass-energy, not classical mass alone. Learn more at source.
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Study Outcomes
Understand the Conservation of Mass -
Define the law of conservation of mass and explain its importance in both chemical reactions and physical changes.
Apply Mass Conservation to Physical Changes -
Calculate and verify mass before and after state transitions to reinforce understanding of matter unit quiz scenarios.
Analyze Mass Relationships in Chemical Reactions -
Balance simple chemical equations and apply mass conservation principles to determine reactant and product masses.
Identify States of Matter and Transitions -
Recognize the key properties of solids, liquids, and gases and describe how phase changes affect mass distribution.
Evaluate Matter Unit Quiz Results -
Interpret your quiz performance data to pinpoint strengths and areas for further study.
Review Mass Conservation Principles for Exam Prep -
Reinforce essential concepts and problem-solving strategies to boost confidence before formal assessments.
Cheat Sheet
Law of Conservation of Mass -
The total mass of reactants equals the total mass of products in a chemical reaction, as established by Antoine Lavoisier and taught in leading university chemistry courses. This principle holds true in both physical and chemical changes, ensuring no atoms are lost or gained. Remember: mass before = mass after, regardless of phase or complexity.
Balancing Chemical Equations -
Every balanced equation illustrates mass conservation by matching atom counts on both sides; for example, 2H₂ + O₂ → 2H₂O shows four hydrogen atoms and two oxygen atoms each side. Practice by adjusting coefficients, not subscripts, to preserve compound identities. A handy tip: balance one element at a time, starting with the most complex molecule.
States of Matter and Phase Changes -
Mass is conserved when a substance shifts state, such as ice melting to water or water boiling to steam, with no loss in a closed system. Familiarize yourself with endothermic and exothermic transitions - energy flows change, but mass remains constant. Use the mnemonic "S L G" (Solid → Liquid → Gas) to trace mass through each reversible phase.
Closed vs. Open Systems -
Conservation of mass strictly applies in closed systems where no matter enters or leaves; open systems can mislead measurements if gases escape or are absorbed. In laboratory practice, using sealed containers or gas traps ensures accurate mass tracking. Always specify system boundaries when calculating mass changes to avoid discrepancies.
Practical Problem-Solving Tips -
Start by listing all reactants and products with their masses or moles before jumping into calculations, a strategy endorsed by top educational repositories like Khan Academy and university resources. Convert masses to moles using M = m/n for consistency when comparing different substances. Finally, double-check algebraic sums to confirm total mass equality.
