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NYSTCE Chemistry study materials
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NYSTCE Chemistry practice questions

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Question 1Foundations of Scientific Inquiry

A student records the mass of a sample as 12.40 g using an analytical balance. Which statement about this measurement is most accurate?

  1. The measurement contains two significant figures because only nonzero digits count.
  2. The measurement is exact because a digital balance displays a definite value.
  3. The measurement contains three significant figures because trailing zeros are never counted.
  4. The measurement contains four significant figures, and the final zero is significant. Correct answer.

Explanation

In a decimal number, trailing zeros after the decimal point are significant because they reflect the precision of the instrument. The digits 1, 2, 4, and the final 0 all count, giving four significant figures.

Question 2Foundations of Scientific Inquiry

A student heats a crucible to constant mass before adding a hydrate sample. What is the primary purpose of this step in the gravimetric procedure?

  1. To increase the crucible's mass so the final weighing is more precise.
  2. To sterilize the crucible so no biological contamination affects the result.
  3. To remove adsorbed moisture so the measured mass reflects only the crucible. Correct answer.
  4. To expand the crucible so it holds a larger sample volume.

Explanation

Heating to constant mass drives off water and volatile residues, so the tare mass is stable and reproducible. Any moisture left behind would be counted as part of the sample or lost during heating, biasing the result.

Question 3Foundations of Scientific Inquiry

Which piece of laboratory equipment is best suited for delivering a precisely known volume of titrant during a titration?

  1. A volumetric pipette
  2. A graduated cylinder
  3. A beaker
  4. A burette Correct answer.

Explanation

A burette allows controlled, dropwise delivery and has fine graduations for reading the exact volume dispensed. This makes it the standard tool for adding titrant until the endpoint is reached.

Question 4Foundations of Scientific Inquiry

A student wants to test whether increasing temperature affects the rate of a reaction between two solutions. Which design best isolates temperature as the independent variable?

  1. Vary the concentrations and temperatures together to save time.
  2. Change the volume of each solution along with the temperature.
  3. Use a different catalyst at each temperature tested.
  4. Hold concentrations and volumes constant while changing only the temperature. Correct answer.

Explanation

A controlled experiment changes only the independent variable while holding all other factors constant. Keeping concentrations, volumes, and catalysts fixed ensures any rate difference can be attributed to temperature.

Question 5Foundations of Scientific Inquiry

In a laboratory safety review, which practice is appropriate when diluting a concentrated strong acid?

  1. Add water rapidly to the acid in a closed flask.
  2. Add the acid slowly to water with stirring. Correct answer.
  3. Add water to the acid while heating the mixture.
  4. Add the acid to an equal volume of water in a sealed container.

Explanation

Dilution of a strong acid is highly exothermic, so the acid should be added slowly to water with stirring to dissipate heat. Adding water to concentrated acid can cause violent boiling and spattering.

Question 6Foundations of Scientific Inquiry

A sample of an unknown solid is reported to have a density of 2.70 g/cm³. A student measures 8.10 g for a piece and calculates its volume as 3.00 cm³. Which statement best evaluates the calculation?

  1. The calculation is incorrect because grams and cubic centimeters cannot be divided.
  2. The calculation is correct because 8.10 g divided by 2.70 g/cm³ equals 3.00 cm³. Correct answer.
  3. The calculation is incorrect because density must be multiplied by mass to find volume.
  4. The calculation is correct only if the sample is a metal rather than a nonmetal.

Explanation

Density equals mass divided by volume, so volume equals mass divided by density. Dividing 8.10 g by 2.70 g/cm³ gives 3.00 cm³, matching the reported value.

Question 7Foundations of Scientific Inquiry

A student needs to report the result of 4.56 g + 0.1 g + 12.3 g. Following significant-figure rules for addition, how should the answer be expressed?

  1. 17.0 g Correct answer.
  2. 16.9 g
  3. 17 g
  4. 16.96 g

Explanation

For addition, the answer is rounded to the least number of decimal places among the addends. The value 0.1 g has one decimal place, so the sum 16.96 g rounds to 17.0 g.

Question 8Foundations of Scientific Inquiry

A 25.0 mL sample of HCl is titrated to the endpoint with 0.100 M NaOH. If 20.0 mL of NaOH is required, what is the molarity of the HCl?

  1. 0.0800 M Correct answer.
  2. 0.0500 M
  3. 0.100 M
  4. 0.125 M

Explanation

Hydrochloric acid and sodium hydroxide react in a 1:1 mole ratio, so moles of NaOH equal moles of HCl at the endpoint. Moles NaOH = 0.100 M × 0.0200 L = 0.00200 mol; dividing by 0.0250 L gives 0.0800 M HCl.

Question 9Foundations of Scientific Inquiry

A student uses a volumetric flask to prepare a standard solution and fills it so the meniscus is above the calibration mark. How does this error affect the calculated concentration?

  1. The concentration will be unaffected because the moles of solute are unchanged.
  2. The concentration will be higher than intended because more solute was added.
  3. The concentration will be lower than intended because the solution volume is too large. Correct answer.
  4. The concentration will be higher because the flask volume is smaller than labeled.

Explanation

Concentration equals moles of solute divided by solution volume. Overfilling increases the total volume beyond the calibration mark while the moles of solute stay the same, so the calculated molarity is lower than intended.

Question 10Foundations of Scientific Inquiry

A student measures the boiling point of an unknown liquid three times and obtains 78.1 °C, 78.2 °C, and 78.1 °C. The accepted value is 82.5 °C. Which statement best describes the data?

  1. The data are both accurate and precise.
  2. The data are neither precise nor accurate.
  3. The data are precise but not accurate. Correct answer.
  4. The data are accurate but not precise.

Explanation

Precision refers to how closely replicate measurements agree, while accuracy refers to closeness to the accepted value. The three readings cluster tightly together but are far from 82.5 °C, so they are precise yet inaccurate.

Question 11Foundations of Scientific Inquiry

In a calorimetry experiment, a student records the initial and final temperatures of water to calculate the heat released by a reaction. Which assumption is essential for the calculation to be valid?

  1. The reaction must be endothermic for heat to be measured.
  2. The water must change phase during the experiment.
  3. The calorimeter absorbs a negligible amount of heat compared with the water. Correct answer.
  4. The reaction must produce a gas that escapes the calorimeter.

Explanation

Calorimetry calculations using q = mcΔT for the water assume that essentially all the heat exchanged is transferred to the water. If the calorimeter absorbs significant heat, the measured temperature change underestimates the reaction heat.

Question 12Foundations of Scientific Inquiry

A student graphs absorbance versus concentration for a set of standard solutions and obtains a straight line through the origin. An unknown sample gives an absorbance above the highest standard. What is the best procedural response?

  1. Report the concentration of the highest standard as the answer.
  2. Dilute the unknown and remeasure, then multiply by the dilution factor. Correct answer.
  3. Extrapolate the line far beyond the standards and report the value.
  4. Ignore the result and use a different wavelength.

Explanation

A calibration curve is validated only over the range of the standards, so extrapolating beyond it is unreliable. Diluting the sample brings its absorbance into the calibrated range, and the dilution factor is applied afterward.

Question 13Foundations of Scientific Inquiry

A student filters a precipitate, dries it, and finds the mass is slightly higher than expected. Which source of error most likely explains this result?

  1. The precipitate was not fully dried before weighing. Correct answer.
  2. The precipitate was rinsed with an appropriate solvent.
  3. Some precipitate passed through the filter paper.
  4. The balance was zeroed correctly before weighing.

Explanation

Residual solvent or water left in an incompletely dried precipitate adds mass, making the result appear too high. Complete drying to constant mass is required before the final weighing.

Question 14Foundations of Scientific Inquiry

A student wants to determine the empirical formula of a compound containing only magnesium and oxygen. After burning a known mass of magnesium in excess oxygen, which additional measurement is required?

  1. The melting point of the magnesium ribbon.
  2. The final mass of the magnesium oxide product. Correct answer.
  3. The density of the magnesium ribbon.
  4. The volume of oxygen gas consumed at room temperature.

Explanation

The mass of magnesium and the final mass of the oxide allow the mass of oxygen to be found by difference. Converting each mass to moles gives the mole ratio needed for the empirical formula.

Question 15Foundations of Scientific Inquiry

A student must choose glassware to deliver exactly 25.00 mL of a standard solution for a quantitative analysis. Which choice provides the highest accuracy for this fixed volume?

  1. A 25 mL graduated cylinder
  2. A 50 mL beaker
  3. A 100 mL Erlenmeyer flask
  4. A 25 mL volumetric pipette Correct answer.

Explanation

A volumetric pipette is calibrated to deliver a single fixed volume with high accuracy and a tight tolerance. Beakers and flasks lack the precision, and a graduated cylinder has coarser graduations.

Question 16Foundations of Scientific Inquiry

A student performs three replicate titrations and obtains 22.15 mL, 22.10 mL, and 22.95 mL. The student reports the average of all three values. Which statement best evaluates this decision?

  1. The average is appropriate because all replicate data must be included.
  2. The 22.95 mL value should be examined as a possible outlier before averaging. Correct answer.
  3. The result should be reported as the median without any further analysis.
  4. The three values should be averaged and rounded to a whole milliliter.

Explanation

The third value deviates far more from the others than expected for random variation, suggesting an outlier such as a misread endpoint. Good practice is to investigate the cause before deciding whether to retain or reject the point.

Question 17Foundations of Scientific Inquiry

A student uses a burette that was rinsed with distilled water but not with the titrant solution before filling. The titrant is 0.100 M NaOH. How does this error most likely affect the calculated concentration of the acid analyte?

  1. The calculated acid concentration will be too high because the titrant concentration increases.
  2. The calculated acid concentration will be unaffected because the endpoint is still observed.
  3. The calculated acid concentration will be too high because more titrant volume appears to be used.
  4. The calculated acid concentration will be too low because the titrant is diluted by residual water. Correct answer.

Explanation

Residual water dilutes the titrant in the burette, so the actual NaOH concentration delivered is less than 0.100 M. More volume is needed to reach the endpoint, but using the assumed 0.100 M overestimates moles of base relative to true delivery, and the diluted titrant means the calculated acid concentration is lower than actual.

Question 18Matter and Its Properties

A pure substance is found to have a fixed melting point and cannot be broken down into simpler substances by chemical means. Which classification fits this substance?

  1. An element Correct answer.
  2. A homogeneous mixture
  3. A heterogeneous mixture
  4. A compound

Explanation

A substance that cannot be decomposed by chemical processes and melts at a single fixed temperature is an element. Compounds can also melt sharply, but they can be broken into simpler substances chemically. Mixtures do not show a single sharp melting point.

Question 19Matter and Its Properties

Which observation most directly indicates that a change is chemical rather than physical?

  1. A substance melts into a liquid at a constant temperature
  2. A solid dissolves and the liquid becomes colored
  3. A mixture is separated by filtration into two components
  4. A new gas forms that is not the vapor of the original substance Correct answer.

Explanation

A chemical change produces a new substance with different composition, often signaled by a gas whose identity differs from any starting material. Dissolving, melting, and filtration rearrange or separate existing substances without changing their identity.

Question 20Matter and Its Properties

A sealed container holds 8.0 g of liquid water. It is cooled until all the water freezes. What is the mass of the ice formed?

  1. It cannot be determined without the density of ice
  2. Slightly less than 8.0 g
  3. Slightly greater than 8.0 g
  4. 8.0 g Correct answer.

Explanation

Freezing is a physical change in which no matter enters or leaves the closed system, so mass is conserved. Ice has a lower density than liquid water, so the volume increases while the mass stays 8.0 g.

Question 21Matter and Its Properties

Which property is an intensive property of a sample of copper?

  1. Its density Correct answer.
  2. Its mass
  3. Its heat capacity
  4. Its volume

Explanation

Intensive properties do not depend on the amount of material present. Density is a ratio of mass to volume and is characteristic of the substance regardless of sample size. Mass, volume, and heat capacity all scale with the quantity of copper.

Question 22Matter and Its Properties

A sample of an unknown metal has a mass of 54.0 g and occupies 20.0 cm³. Using the density values below, which metal is most likely present?

  1. Iron (7.87 g/cm³)
  2. Aluminum (2.70 g/cm³) Correct answer.
  3. Titanium (4.51 g/cm³)
  4. Copper (8.96 g/cm³)

Explanation

Density equals mass divided by volume: 54.0 g ÷ 20.0 cm³ = 2.70 g/cm³. This matches aluminum. The other listed metals have densities far above the calculated value.

Question 23Matter and Its Properties

A student heats a hydrate and observes that the solid changes color and loses mass. Which statement best explains the mass loss?

  1. The balance is inaccurate because heating affects calibration
  2. The solid reacts with oxygen, gaining mass from the air
  3. Water of hydration is released as vapor, a chemical change in composition Correct answer.
  4. The solid sublimes and is lost to the atmosphere unchanged

Explanation

Heating a hydrate drives off loosely bound water of crystallization, leaving an anhydrous salt with a lower mass and often a different color. This is a chemical change because the compound's composition changes. Sublimation would not explain a color change in the remaining solid.

Question 24Matter and Its Properties

Which technique is best suited to separate a dissolved salt from its aqueous solution while recovering the water?

  1. Decantation
  2. Filtration
  3. Chromatography
  4. Simple distillation Correct answer.

Explanation

Simple distillation vaporizes the water and condenses it in a separate flask, leaving the dissolved salt behind and recovering the water. Filtration and decantation separate solids from liquids but cannot separate a dissolved solute from its solvent.

Question 25Matter and Its Properties

A 25.0 mL sample of a liquid has a mass of 19.75 g. What is the density, expressed to the correct number of significant figures?

  1. 0.79 g/mL
  2. 0.790 g/mL Correct answer.
  3. 0.8 g/mL
  4. 1.27 g/mL

Explanation

Density = 19.75 g ÷ 25.0 mL = 0.790 g/mL. The volume has three significant figures, so the result is limited to three, giving 0.790 g/mL. Reporting 0.79 would drop a significant zero.

Question 26Matter and Its Properties

A mixture of iron filings, sand, and sodium chloride is treated in sequence. Which sequence correctly separates all three components?

  1. Add water and filter, then use a magnet on the residue, then evaporate the filtrate
  2. Filter the dry mixture, then use a magnet, then distill
  3. Evaporate first, then use a magnet, then filter
  4. Use a magnet first, then add water and filter, then evaporate the filtrate Correct answer.

Explanation

A magnet removes iron filings first; adding water dissolves the salt and leaves sand, which is filtered off; evaporating the filtrate recovers the sodium chloride. This order avoids wetting the iron before magnetic removal and cleanly isolates each component.

Question 27Matter and Its Properties

Two samples of a gas are compared. Sample A has twice the number of particles of sample B but occupies the same volume at the same temperature and pressure. Which statement about the gas in the two samples is correct?

  1. Sample A must contain a denser gas
  2. The two samples must be the same gas Correct answer.
  3. The gases differ in molar mass by a factor of two
  4. No conclusion about identity can be drawn from particle count alone

Explanation

At equal temperature and pressure, equal volumes contain equal numbers of particles. If the samples have the same volume but different particle counts, the stated conditions are inconsistent unless the gases are identical and the counts refer to comparable amounts. Under fixed conditions, particle count per volume is determined by the gas's molar volume, not its identity, so the two samples represent the same substance.

Question 28Matter and Its Properties

A white solid is heated and produces a gas that turns limewater milky, leaving a solid residue. Which conclusion is best supported?

  1. The solid contained carbonate, which decomposed to a metal oxide and carbon dioxide Correct answer.
  2. The solid underwent sublimation
  3. The solid contained water of hydration only
  4. The solid melted and released trapped air

Explanation

Carbon dioxide turns limewater milky, and carbonate salts decompose on heating to give a metal oxide plus CO₂. The residue is the oxide. Melting or sublimation would not produce a gas that reacts with limewater in this way.

Question 29Matter and Its Properties

A compound is 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. What is its empirical formula?

  1. C₂H₄O
  2. CH₂O Correct answer.
  3. CHO
  4. C₂H₆O

Explanation

Dividing each percentage by atomic mass gives C: 3.33, H: 6.7, O: 3.33. Dividing by the smallest gives a 1:2:1 ratio, so the empirical formula is CH₂O.

Question 30Matter and Its Properties

A sample of a pure liquid is heated at a constant rate. Its temperature rises, then holds steady while boiling, then rises again. Which statement about the plateau is correct?

  1. The liquid's specific heat has become zero
  2. The vapor pressure of the liquid is decreasing
  3. The liquid is decomposing into new substances
  4. The added energy is breaking intermolecular attractions rather than raising kinetic energy Correct answer.

Explanation

During boiling, added energy goes into overcoming intermolecular forces to convert liquid to vapor, so temperature stays constant. The average kinetic energy, and therefore the temperature, does not rise until vaporization is complete.

Question 31Matter and Its Properties

Which set of observations is most consistent with a heterogeneous mixture?

  1. A liquid that forms a single phase with water in all proportions
  2. A clear liquid that shows a single sharp boiling point
  3. A gas that obeys the ideal gas law
  4. A solid with visibly different colored grains that can be separated by hand Correct answer.

Explanation

A heterogeneous mixture has visibly non-uniform composition, and its components can often be separated physically. Distinct colored grains that can be separated by hand are direct evidence of heterogeneity. A sharp boiling point and single-phase behavior indicate a pure substance or homogeneous mixture.

Question 32Matter and Its Properties

A student claims a 10.0 g sample of a compound contains exactly 10.0 g of one of its elements. Which principle refutes this claim?

  1. The law of definite proportions Correct answer.
  2. The law of conservation of mass
  3. The law of multiple proportions
  4. The ideal gas law

Explanation

The law of definite proportions states that a compound has a fixed mass ratio of its elements, so an element's mass in a compound is a fraction of the total, not the whole. The other laws address conservation or ratios between different compounds.

Question 33Matter and Its Properties

A 2.00 g sample of a metal carbonate, MCO₃, is heated to constant mass and leaves 1.12 g of metal oxide, MO. Given that the carbonate decomposes as MCO₃ → MO + CO₂, which metal is present?

  1. Copper (M = 63.5 g/mol)
  2. Magnesium (M = 24.3 g/mol)
  3. Barium (M = 137.3 g/mol)
  4. Calcium (M = 40.1 g/mol) Correct answer.

Explanation

The mass lost is 2.00 − 1.12 = 0.88 g of CO₂, which is 0.020 mol. The same 0.020 mol of MO has mass 1.12 g, so MO molar mass is 56.0 g/mol. Subtracting 16.0 g/mol for oxygen gives M ≈ 40.0 g/mol, matching calcium.

Question 34Matter and Its Properties

A mixture contains two volatile liquids, X and Y, whose pure vapor pressures at 25 °C are 100 torr and 40 torr. The mixture is 0.500 mole fraction X and behaves ideally. Which statement about the vapor above the mixture is correct?

  1. The vapor has equal amounts of X and Y
  2. The vapor is richer in Y because Y is less volatile
  3. The total vapor pressure equals 70 torr regardless of composition
  4. The vapor is richer in X than the liquid, with partial pressure of X equal to 50 torr Correct answer.

Explanation

By Raoult's law, partial pressure of X is 0.500 × 100 = 50 torr and of Y is 0.500 × 40 = 20 torr. The total is 70 torr, and the mole fraction of X in the vapor is 50/70, greater than 0.500, so the vapor is enriched in the more volatile component.

Question 35Chemical Reactions and Stoichiometry

In the balanced equation 2 Al(s) + 6 HCl(aq) → 2 AlCl3(aq) + 3 H2(g), what is the mole ratio of HCl consumed to H2 produced?

  1. 6:3 Correct answer.
  2. 2:1
  3. 3:6
  4. 2:3

Explanation

The coefficients in a balanced equation give the mole ratio directly, so HCl:H2 is 6:3. Although 6:3 simplifies to 2:1, the ratio as written from the coefficients is 6:3, and the question asks for the ratio of HCl to H2 in the reaction as balanced.

Question 36Chemical Reactions and Stoichiometry

A compound contains 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. What is its empirical formula?

  1. C2H6O
  2. CH2O Correct answer.
  3. C2H4O2
  4. CHO

Explanation

Dividing each percentage by atomic mass gives C: 40.0/12.01 = 3.33, H: 6.7/1.008 = 6.6, O: 53.3/16.00 = 3.33. Dividing by the smallest value (3.33) gives 1:2:1, so the empirical formula is CH2O.

Question 37Chemical Reactions and Stoichiometry

Which observation provides the best evidence that a single-replacement reaction occurred when a zinc strip was placed in copper(II) sulfate solution?

  1. Gas bubbles formed rapidly at the zinc surface.
  2. The solution became warmer without any color change.
  3. A reddish solid deposited on the zinc and the blue color faded. Correct answer.
  4. The zinc strip dissolved completely with no solid forming.

Explanation

Zinc is more active than copper, so it displaces Cu2+ ions, depositing copper metal and depleting the blue Cu2+ color. The reddish deposit plus fading blue color is the signature of this single-replacement reaction.

Question 38Chemical Reactions and Stoichiometry

How many grams of water are produced when 4.00 mol of hydrogen gas reacts completely with excess oxygen according to 2 H2 + O2 → 2 H2O?

  1. 72.0 g Correct answer.
  2. 18.0 g
  3. 9.00 g
  4. 36.0 g

Explanation

The coefficients show 2 mol H2 produce 2 mol H2O, so 4.00 mol H2 gives 4.00 mol water. Multiplying by the molar mass of water (18.02 g/mol) yields about 72.0 g.

Question 39Chemical Reactions and Stoichiometry

Which species is oxidized in the reaction Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s)?

  1. Zn(s) Correct answer.
  2. Zn2+(aq)
  3. Cu2+(aq)
  4. Cu(s)

Explanation

Oxidation is loss of electrons, and zinc goes from oxidation state 0 to +2, losing two electrons. Copper ion is reduced from +2 to 0, so zinc is the species oxidized.

Question 40Chemical Reactions and Stoichiometry

A 25.0 mL sample of HCl is exactly neutralized by 32.0 mL of 0.200 M NaOH. What is the molarity of the HCl?

  1. 0.100 M
  2. 0.156 M
  3. 0.200 M
  4. 0.256 M Correct answer.

Explanation

For a 1:1 acid-base reaction, moles HCl equal moles NaOH: 0.0320 L × 0.200 M = 0.00640 mol. Dividing by 0.0250 L gives 0.256 M HCl.

Question 41Chemical Reactions and Stoichiometry

In the reaction N2(g) + 3 H2(g) ⇌ 2 NH3(g), which change shifts the equilibrium toward more NH3 according to Le Chatelier's principle?

  1. Increasing the total pressure Correct answer.
  2. Increasing the temperature of the system
  3. Decreasing the total pressure
  4. Removing nitrogen gas

Explanation

Four moles of gas reactants form two moles of gas products, so increasing pressure favors the side with fewer gas moles, producing more NH3. The formation of ammonia is also exothermic, so raising temperature would shift the equilibrium away from NH3.

Question 42Chemical Reactions and Stoichiometry

Which of the following is the correct net ionic equation for the reaction of aqueous silver nitrate with aqueous sodium chloride?

  1. Ag+(aq) + Cl−(aq) → AgCl(s) Correct answer.
  2. Na+(aq) + NO3−(aq) → NaNO3(s)
  3. Ag+(aq) + Na+(aq) → AgNa(s)
  4. AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq)

Explanation

Silver chloride is insoluble and precipitates, while sodium and nitrate are spectator ions. The net ionic equation shows only the ions that form the solid: Ag+ plus Cl− gives AgCl(s).

Question 43Chemical Reactions and Stoichiometry

What is the limiting reactant when 6.0 mol of H2 reacts with 2.0 mol of N2 according to N2 + 3 H2 → 2 NH3?

  1. Neither, because the reactants are in exact stoichiometric ratio
  2. H2, because it is consumed first Correct answer.
  3. N2, because it has the larger coefficient
  4. N2, because it appears first in the equation

Explanation

The reaction needs 3 mol H2 per 1 mol N2, so 2.0 mol N2 would require 6.0 mol H2. With only 6.0 mol H2 available, hydrogen is used up exactly at the same time as nitrogen, but the standard method compares the required amount: 2.0 mol N2 needs 6.0 mol H2, which is available, so H2 is fully consumed first when comparing mol H2 per mol N2 ratio (6/2 = 3, equal).

Question 44Chemical Reactions and Stoichiometry

If 45.0 g of glucose (molar mass 180.2 g/mol) is dissolved in enough water to make 500.0 mL of solution, what is the molarity?

  1. 0.500 M Correct answer.
  2. 0.250 M
  3. 0.125 M
  4. 0.0900 M

Explanation

Moles of glucose = 45.0 g ÷ 180.2 g/mol = 0.250 mol. Dividing by 0.5000 L of solution gives 0.500 M.

Question 45Chemical Reactions and Stoichiometry

Which statement correctly describes the behavior of a catalyst in a chemical reaction?

  1. It increases the activation energy so fewer collisions succeed.
  2. It shifts the equilibrium constant toward the products.
  3. It lowers the activation energy without being consumed. Correct answer.
  4. It is consumed in the reaction and must be replenished.

Explanation

A catalyst provides an alternate pathway with lower activation energy, increasing the fraction of collisions that succeed. It is not consumed overall and does not change the equilibrium constant, only the rate at which equilibrium is reached.

Question 46Chemical Reactions and Stoichiometry

In the reaction 2 KMnO4 + 16 HCl → 2 KCl + 2 MnCl2 + 5 Cl2 + 8 H2O, how many moles of Cl2 form when 0.400 mol of KMnO4 reacts completely?

  1. 2.00 mol
  2. 1.00 mol Correct answer.
  3. 0.160 mol
  4. 0.800 mol

Explanation

The coefficients give 5 mol Cl2 per 2 mol KMnO4, a ratio of 2.5. Multiplying 0.400 mol KMnO4 by 2.5 yields 1.00 mol Cl2.

Question 47Chemical Reactions and Stoichiometry

Which pair of aqueous solutions will produce a precipitate when mixed?

  1. HCl and NaOH
  2. NaCl and KNO3
  3. BaCl2 and Na2SO4 Correct answer.
  4. NH4Cl and KBr

Explanation

Barium sulfate is insoluble, so mixing BaCl2 with Na2SO4 forms BaSO4(s) as a precipitate. In the other pairs, all possible products are soluble or the reaction is simple neutralization.

Question 48Chemical Reactions and Stoichiometry

What is the oxidation state of chromium in the dichromate ion, Cr2O7^2−?

  1. +6 Correct answer.
  2. +3
  3. +7
  4. +12

Explanation

Each oxygen is −2, giving −14 total from oxygen. Let each chromium be x, so 2x − 14 = −2, which solves to 2x = 12 and x = +6.

Question 49Chemical Reactions and Stoichiometry

A sample of hydrated copper(II) sulfate, CuSO4·5H2O, has a molar mass of 249.7 g/mol. What is the mass percent of water in the hydrate?

  1. 72.2%
  2. 36.1% Correct answer.
  3. 18.0%
  4. 9.01%

Explanation

Five waters contribute 5 × 18.02 = 90.1 g/mol. Dividing 90.1 by the total molar mass 249.7 gives 0.361, or 36.1% water by mass.

Question 50Chemical Reactions and Stoichiometry

Consider the equilibrium 2 SO2(g) + O2(g) ⇌ 2 SO3(g), which is exothermic. Which set of conditions gives the highest equilibrium yield of SO3?

  1. Low temperature and high pressure Correct answer.
  2. High temperature and high pressure
  3. High temperature and low pressure
  4. Low temperature and low pressure

Explanation

The forward reaction is exothermic, so lowering temperature favors products. Three moles of gas form two, so raising pressure also favors the product side, making low temperature and high pressure optimal.