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FTCE Chemistry 6-12 study materials
FTCE Chemistry 6-12 study resources

FTCE Chemistry 6-12 practice questions

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Question 1Scientific Inquiry and Processes

A student records the volume of a liquid as 24.6 mL using a graduated cylinder marked in 1 mL increments. Which statement best describes the uncertainty of this measurement?

  1. No uncertainty exists because the value has one decimal place.
  2. The measurement has an estimated digit, so uncertainty is about ±0.1 mL. Correct answer.
  3. The measurement is exact because the cylinder has markings.
  4. The uncertainty equals the full marked increment of ±1 mL.

Explanation

When reading an analog scale, the last recorded digit is estimated to about one-tenth of the smallest marked division. With 1 mL markings, the estimate is reliable to roughly ±0.1 mL, so 24.6 mL reflects that precision.

Question 2Scientific Inquiry and Processes

A chemistry teacher wants to demonstrate that a reaction is exothermic. Which observation most directly supports that conclusion?

  1. A precipitate forms and settles at the bottom.
  2. The temperature of the surroundings increases during the reaction. Correct answer.
  3. The reaction produces a gas that bubbles from the mixture.
  4. The reaction mixture becomes colder than the surroundings.

Explanation

An exothermic reaction releases energy to the surroundings, raising their temperature. Gas production and precipitate formation indicate chemical change but say nothing about the sign of the enthalpy change.

Question 3Scientific Inquiry and Processes

Which piece of safety equipment should be used first when a small fire erupts in a beaker on a laboratory bench?

  1. The eyewash station
  2. The fume hood
  3. The fire extinguisher Correct answer.
  4. The fire blanket

Explanation

A fire extinguisher is the appropriate first response for a bench-top fire, directed at the base of the flames. Eyewash stations and blankets serve different emergencies, and a fume hood does not extinguish fire.

Question 4Scientific Inquiry and Processes

A student wants to determine the density of an irregularly shaped metal sample. Which procedure yields the most reliable density value?

  1. Measure the mass on a balance and estimate the volume from the sample's appearance.
  2. Measure the mass on a balance and the volume by water displacement in a graduated cylinder. Correct answer.
  3. Weigh the sample in air and again in water without recording the water temperature.
  4. Measure the length and width with a ruler and multiply by an assumed height.

Explanation

Density equals mass divided by volume, and water displacement gives the volume of an irregular solid accurately. Mass from a balance plus displaced volume combines two direct measurements with known precision.

Question 5Scientific Inquiry and Processes

In a controlled experiment testing how temperature affects the rate of a reaction, which variable must be deliberately held constant?

  1. The controlled variables Correct answer.
  2. The hypothesis
  3. The independent variable
  4. The dependent variable

Explanation

Controlled variables are factors other than the independent variable that are kept constant so they do not confound the result. The independent variable is deliberately varied, and the dependent variable is measured.

Question 6Scientific Inquiry and Processes

Which statement correctly describes the role of a control group in an experiment?

  1. It is selected after the data are collected.
  2. It provides a baseline for comparison without the treatment. Correct answer.
  3. It receives the experimental treatment at a higher dose.
  4. It is always the group with the largest sample size.

Explanation

A control group is not exposed to the independent variable and establishes the baseline against which treatment effects are judged. Without it, observed changes cannot be attributed to the treatment.

Question 7Scientific Inquiry and Processes

A student reports a measured value of 0.004560 g. How many significant figures does this value contain?

  1. Four Correct answer.
  2. Three
  3. Six
  4. Seven

Explanation

Leading zeros before the first nonzero digit are not significant, but trailing zeros after the decimal point are. The significant digits are 4, 5, 6, and 0, giving four significant figures.

Question 8Scientific Inquiry and Processes

Which type of graph is most appropriate for displaying the distribution of a single continuous variable such as the melting points of a set of compounds?

  1. A scatter plot of two variables
  2. A histogram Correct answer.
  3. A line graph with connected points
  4. A pie chart

Explanation

A histogram bins a continuous variable and shows how frequently values fall in each interval, revealing the distribution's shape. Pie charts and two-variable scatter plots serve different purposes.

Question 9Scientific Inquiry and Processes

A chemist obtains the following replicate measurements of a standard solution's concentration: 0.102, 0.103, and 0.102 mol/L. The accepted value is 0.118 mol/L. Which statement best characterizes the data?

  1. The data are both accurate and precise.
  2. The data are accurate but imprecise.
  3. The data are precise but inaccurate. Correct answer.
  4. The data are neither precise nor accurate.

Explanation

Precision refers to how closely replicates agree, and these three values cluster tightly together. Accuracy refers to closeness to the accepted value, and all three are well below 0.118 mol/L, so the data are precise but inaccurate.

Question 10Scientific Inquiry and Processes

A student calculates a result of 0.03456 mol using measured values with three significant figures. How should the result be reported?

  1. 0.035 mol
  2. 0.0346 mol Correct answer.
  3. 0.03456 mol
  4. 0.03 mol

Explanation

A calculation result should be rounded to the same number of significant figures as the least precise measurement. Three significant figures in 0.03456 mol gives 0.0346 mol.

Question 11Scientific Inquiry and Processes

A student claims that adding more solute always increases the conductivity of a solution. Which experimental result would most directly test this claim?

  1. Measuring the mass of undissolved solid remaining after each addition.
  2. Measuring the solution's boiling point at a single concentration.
  3. Measuring the solution's conductivity at several solute concentrations. Correct answer.
  4. Measuring the pH of the solution at several solute concentrations.

Explanation

The claim concerns conductivity, so the dependent variable must be conductivity measured across a range of solute concentrations. Varying concentration while measuring conductivity directly tests the proposed relationship.

Question 12Scientific Inquiry and Processes

A chemistry class collects the following data for a reaction at increasing temperatures. To determine whether temperature significantly affects reaction rate, which analysis is most appropriate?

  1. Plot the temperatures on a pie chart.
  2. Report only the single highest rate observed.
  3. Calculate the mean rate at each temperature and compare the trends with error bars. Correct answer.
  4. Average all rates across all temperatures into one value.

Explanation

Comparing mean rates at each temperature with error bars shows both the trend and the variability, allowing a judgment about significance. Collapsing all data into one value or selecting the maximum destroys the relationship being tested.

Question 13Scientific Inquiry and Processes

A student uses a pH meter to measure a solution and records 7.2, then 7.4, then 7.3 on repeated trials. Which action would most improve the reliability of the reported value?

  1. Rounding each value to the nearest whole number.
  2. Reporting the first value because it was measured first.
  3. Recording more trials and reporting the mean with its uncertainty. Correct answer.
  4. Changing the meter's calibration between each trial.

Explanation

Reliability improves when more replicate measurements are averaged and the spread is reported as uncertainty. Rounding, using only one trial, or altering calibration mid-series reduces confidence rather than improving it.

Question 14Scientific Inquiry and Processes

A student dissolves a sample in water and the solution becomes warm. Which conclusion is best supported by this observation alone?

  1. The sample did not dissolve.
  2. The dissolution process is exothermic. Correct answer.
  3. The dissolution process is endothermic.
  4. The sample reacted to form a gas.

Explanation

A temperature rise of the solution indicates that the dissolution released energy to the surroundings, which defines an exothermic process. No gas or undissolved solid is implied by warmth alone.

Question 15Scientific Inquiry and Processes

Which statement best explains why repeated measurements reduce the effect of random error?

  1. Each repetition increases the significance of the final digit.
  2. Averaging removes the need for calibration.
  3. Random errors cancel in the average, so the mean approaches the true value. Correct answer.
  4. Repeated measurements eliminate systematic error from the instrument.

Explanation

Random errors scatter above and below the true value, so averaging many trials tends to cancel them and yield a mean closer to the true value. Systematic error, by contrast, is not reduced by repetition.

Question 16Scientific Inquiry and Processes

A student wants to separate a mixture of sand and dissolved salt. Which sequence of techniques is most appropriate?

  1. Distillation followed by filtration
  2. Chromatography followed by distillation
  3. Filtration followed by evaporation Correct answer.
  4. Evaporation followed by filtration

Explanation

Filtration removes the insoluble sand, and evaporation of the filtrate recovers the dissolved salt. Reversing the order would leave salt mixed with sand during evaporation.

Question 17Scientific Inquiry and Processes

A student plots concentration versus absorbance for a set of standard solutions and obtains a straight line through the origin. A sample's absorbance falls within the range of the standards. Which conclusion is justified?

  1. The sample contains no absorbing species.
  2. The sample is more concentrated than the most concentrated standard.
  3. The sample concentration can be found from the calibration line. Correct answer.
  4. The calibration line proves the sample is pure.

Explanation

A linear calibration through the origin within the standard range allows interpolation of an unknown concentration from its absorbance. Extrapolation beyond the standards or claims about purity are not supported.

Question 18Scientific Inquiry and Processes

Which experimental design best tests whether a catalyst increases the rate of decomposition of hydrogen peroxide?

  1. Run the reaction only with the catalyst and record the time.
  2. Run the reaction at several temperatures without a catalyst.
  3. Run the reaction with two different catalysts at different concentrations.
  4. Run the reaction with and without the catalyst while holding temperature and concentration constant. Correct answer.

Explanation

To isolate the catalyst's effect, the only difference between trials must be the presence of the catalyst while other factors are held constant. Varying temperature or concentration introduces confounding variables.

Question 19Scientific Inquiry and Processes

A student heats a hydrate and observes a constant mass after several minutes of heating. What does the constant mass indicate about the experiment?

  1. The hydrate has decomposed into a new compound.
  2. The sample has melted.
  3. The balance is malfunctioning.
  4. All water of hydration has been driven off. Correct answer.

Explanation

A constant mass signals that no further volatile component is being lost, which for a hydrate means the water of hydration has been fully removed. Continued heating without mass change indicates completion.

Question 20Scientific Inquiry and Processes

A student measures the boiling point of a liquid at a high-altitude location and finds it lower than at sea level. Which explanation is correct?

  1. The liquid's molar mass decreases at altitude.
  2. The liquid has a higher vapor pressure at altitude.
  3. The atmospheric pressure is lower, so the liquid boils at a lower temperature. Correct answer.
  4. The thermometer reads incorrectly at altitude.

Explanation

Boiling occurs when the vapor pressure equals the external pressure. At high altitude the external pressure is lower, so the liquid reaches that pressure at a lower temperature.

Question 21Scientific Inquiry and Processes

A researcher reports a result with a stated uncertainty of ±0.05 g. Which interpretation of this uncertainty is most appropriate?

  1. The uncertainty equals the significant-figure count.
  2. The measurement is likely within 0.05 g of the true value. Correct answer.
  3. The true value lies exactly 0.05 g from the measured value.
  4. The measurement has no error.

Explanation

A stated uncertainty expresses the range within which the true value is expected to lie, typically at a stated confidence level. It is an estimate of error magnitude, not a guarantee of the exact deviation.

Question 22Scientific Inquiry and Processes

A student analyzes a reaction and finds the rate doubles when the concentration of one reactant doubles while the other reactant's concentration is held constant. What is the reaction order with respect to that reactant?

  1. Second order
  2. Third order
  3. Zero order
  4. First order Correct answer.

Explanation

When doubling a reactant's concentration doubles the rate, the rate is directly proportional to that concentration, which defines first order. Zero order would show no change, and second order would quadruple the rate.

Question 23Scientific Inquiry and Processes

A student titrates a weak acid with a strong base and observes that the equivalence point occurs at pH greater than 7. Which explanation is correct?

  1. The indicator changes color before neutralization.
  2. The conjugate base produced hydrolyzes water to generate hydroxide ion. Correct answer.
  3. The weak acid does not react with the base.
  4. The strong base is in excess at the equivalence point.

Explanation

At the equivalence point of a weak acid–strong base titration, the conjugate base remains and reacts with water to produce hydroxide ion, raising the pH above 7. This is a hydrolysis effect, not excess base.

Question 24Scientific Inquiry and Processes

A chemist needs to determine the enthalpy change of a reaction using a coffee-cup calorimeter. Which assumption is essential to the calculation?

  1. The reaction goes to completion instantly.
  2. The pressure changes significantly during the reaction.
  3. The calorimeter absorbs a negligible amount of heat. Correct answer.
  4. The solution's specific heat is zero.

Explanation

A coffee-cup calorimeter is treated as an isolated system in which heat exchanged with the calorimeter itself is negligible, so the measured heat change of the solution equals the reaction's enthalpy change. A nonzero specific heat is required, not zero.

Question 25Scientific Inquiry and Processes

A student compares two data sets with identical means but different standard deviations. Which conclusion is best supported?

  1. The set with the smaller standard deviation has values clustered more tightly about the mean. Correct answer.
  2. The set with the larger standard deviation is more accurate.
  3. The means prove the two sets are identical.
  4. Both sets must have identical ranges.

Explanation

Standard deviation measures the spread of values about the mean, so a smaller value indicates tighter clustering. Identical means say nothing about spread, accuracy, or range.

Question 26Scientific Inquiry and Processes

A laboratory instructor asks students to determine the density of an unknown metal. Which practice best supports the reliability of the reported value?

  1. Repeating the mass and volume measurements several times and reporting the mean with its spread Correct answer.
  2. Rounding each calculated density to the nearest whole number before averaging
  3. Recording only the trials whose results agree with the accepted density of aluminum
  4. Measuring the mass and volume once with the most precise instruments available

Explanation

Reliability reflects how reproducible a measurement is, so multiple independent trials with an estimate of variability are required. Reporting the mean together with the spread conveys both the central value and the precision of the procedure.

Question 27Scientific Inquiry and Processes

A student must transfer exactly 25.00 mL of a standard solution for a titration. Which piece of glassware is designed to deliver that volume with the highest accuracy?

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

Explanation

A volumetric (transfer) pipet is calibrated to deliver one fixed volume with very small tolerance, making it the standard choice for aliquot transfer in titrations. Graduated cylinders and general containers have much larger tolerances.

Question 28Scientific Inquiry and Processes

During a flame test, a student holds a platinum wire in the oxidizing (outer) region of a Bunsen flame rather than the reducing inner cone. What is the main analytical reason for this choice?

  1. The outer flame is hotter and oxidizing, minimizing interference from reduced species and soot Correct answer.
  2. The outer flame is cooler, so the sample volatilizes more slowly and evenly
  3. The outer flame emits no visible light that could mask the metal's color
  4. The inner cone contains more oxygen and therefore gives a brighter emission

Explanation

The oxidizing outer region is hotter and supports complete combustion, so contaminants burn away and the metal's characteristic emission is not masked by reduced species or glowing soot. The inner cone is cooler and reducing, which can interfere with the observed color.

Question 29Scientific Inquiry and Processes

A student is asked to prepare 250.0 mL of a 0.100 M solution from a concentrated stock. Which sequence of steps is most appropriate?

  1. Add water to the flask first, then the stock, then more water to the mark
  2. Add the calculated stock volume to a 250 mL volumetric flask, then add water to the mark and mix Correct answer.
  3. Measure the stock in a graduated cylinder, pour into a beaker, add 250 mL water, and stir
  4. Dilute the stock in a beaker, then transfer to a flask and fill to the mark without mixing

Explanation

Accurate dilution requires delivering the stock into a volumetric flask, then adding solvent to the calibration mark and inverting to mix, so the final volume is exactly 250.0 mL. Adding water first or measuring final volume in a beaker changes the total volume and the concentration.

Question 30Scientific Inquiry and Processes

A student uses a buret that was rinsed with distilled water but not with the titrant before filling. How does this affect the calculated concentration of the unknown?

  1. The delivered titrant is diluted, so less volume is needed and the calculated concentration is too low
  2. The calculated concentration is unaffected because the titrant concentration is known
  3. The unknown solution is diluted, so the calculated concentration is too low
  4. The delivered titrant is diluted, so more volume is needed and the calculated concentration is too high Correct answer.

Explanation

Residual water dilutes the titrant, so a larger buret volume is required to reach the endpoint. Because the calculation uses the nominal titrant molarity with an inflated volume, the computed amount of analyte and its concentration come out too high.

Question 31Scientific Inquiry and Processes

A student records the volume of a gas as 42.5 mL using a graduated cylinder whose smallest divisions are 1 mL. Which statement best describes the uncertainty of this reading?

  1. The reading is exact because the cylinder has printed graduations
  2. The uncertainty cannot be estimated without a digital display
  3. The last digit is estimated, so the uncertainty is roughly ±0.5 mL Correct answer.
  4. The uncertainty is ±1 mL because that is the smallest division

Explanation

On an analog scale, the final recorded digit is an estimate between the smallest markings, conventionally about one-tenth of a division or half a division. With 1 mL divisions, the reading is reasonably reported to ±0.5 mL.

Question 32Scientific Inquiry and Processes

A student obtains a percent yield of 112% for a synthesis. Which explanation is most consistent with good laboratory practice?

  1. The limiting reactant was fully consumed
  2. Some product was lost during filtration
  3. The reaction did not go to completion
  4. The product was weighed while still wet with solvent Correct answer.

Explanation

A yield above 100% indicates more mass than theoretically possible, typically because the product retains solvent or other impurities. Drying to constant mass before weighing is the standard remedy.

Question 33Scientific Inquiry and Processes

A chemist needs to monitor how the absorbance of a reaction mixture changes continuously over 30 minutes. Which instrument and setup is most appropriate?

  1. A balance recording mass every 5 minutes
  2. A pH meter with a data logger
  3. A spectrophotometer set to the analyte's absorption maximum Correct answer.
  4. A thermometer placed in the cuvette

Explanation

Absorbance is measured with a spectrophotometer, and using the wavelength of maximum absorption maximizes sensitivity and minimizes relative error. Continuous readings track concentration through Beer's law.

Question 34Scientific Inquiry and Processes

A student wants to determine whether a new fertilizer increases plant growth while controlling for confounding variables. Which design is strongest?

  1. Apply fertilizer to the largest plants and compare with the smallest
  2. Treat ten plants with fertilizer and compare them with ten untreated plants grown in the same conditions Correct answer.
  3. Treat all plants with fertilizer and record growth over time
  4. Compare plants grown outdoors in summer with plants grown indoors in winter

Explanation

A controlled comparison requires treated and untreated groups kept under identical conditions except for the independent variable, so any growth difference can be attributed to the fertilizer. Matching all other conditions isolates the treatment effect.

Question 35Scientific Inquiry and Processes

A student heats a crucible containing a metal carbonate to constant mass, then calculates the mass of CO2 released. Which precaution most directly improves the accuracy of that calculated mass?

  1. Heating for a shorter total time
  2. Cooling the crucible in a desiccator before each weighing Correct answer.
  3. Using a larger sample mass than required
  4. Weighing the crucible while still hot from the flame

Explanation

A hot crucible can absorb moisture and its buoyancy changes, so cooling in a desiccator before weighing prevents mass drift. Weighing to constant mass ensures complete decomposition and a reliable CO2 mass by difference.

Question 36Scientific Inquiry and Processes

A student compares the precision of two analytical balances by weighing the same object ten times on each. Which statistic best quantifies precision for this comparison?

  1. The difference between the two means
  2. The standard deviation of the ten readings on each balance Correct answer.
  3. The range of the object's accepted mass
  4. The mean of the ten readings on each balance

Explanation

Precision describes the closeness of replicate measurements to one another, which the standard deviation quantifies directly. A smaller standard deviation indicates a more precise instrument.

Question 37Scientific Inquiry and Processes

A student's calibration curve for copper(II) ion has a correlation coefficient of 0.999 but the y-intercept is far from zero. What is the most appropriate interpretation?

  1. The data are invalid because R is below 1.000
  2. The correlation coefficient proves the method is accurate
  3. The curve should be forced through the origin regardless of the data
  4. The standards are precise but there is a systematic offset that should be investigated Correct answer.

Explanation

A high correlation coefficient indicates strong linearity but says nothing about accuracy, and a large nonzero intercept suggests a blank or reagent contribution. The offset should be identified and corrected before using the curve quantitatively.

Question 38Scientific Inquiry and Processes

A student must safely heat a flammable organic liquid in the laboratory. Which approach is most appropriate?

  1. Using a hot plate set to maximum in a fume hood
  2. Using a heating mantle or water bath with no open flame Correct answer.
  3. Heating in a sealed flask with a stopper
  4. Heating over an open Bunsen burner flame

Explanation

Flammable liquids must be heated with spark-free sources such as a heating mantle or water bath, away from open flames. This prevents ignition of vapors that accumulate above the liquid.

Question 39Scientific Inquiry and Processes

A student finds that a titration endpoint fades after 20 seconds of swirling. Which action is most appropriate?

  1. Add more titrant dropwise until the color persists, then record the volume Correct answer.
  2. Record the volume as the endpoint and stop
  3. Discard the trial and begin again with a fresh sample
  4. Add titrant rapidly to reach a darker color

Explanation

A fading color indicates the endpoint has not been reached; the indicator is returning to its original form. Continuing dropwise until the color persists for about 30 seconds ensures a true endpoint.

Question 40Scientific Inquiry and Processes

A researcher reports a mean of 12.4 g with a standard deviation of 0.3 g for five trials. Which statement best interprets this result?

  1. The individual measurements are typically about 0.3 g from the mean, and the standard error is smaller Correct answer.
  2. The five trials are insufficient to compute a standard deviation
  3. The true value must lie between 12.1 g and 12.7 g
  4. The measurement is accurate because the standard deviation is small

Explanation

The standard deviation describes the typical scatter of individual measurements about the mean, while the standard error of the mean, s divided by the square root of n, is smaller. A small standard deviation indicates precision, not accuracy.

Question 41Matter and Its Changes

Which statement correctly describes a chemical change rather than a physical change in a sample of matter?

  1. The sample changes shape but its molecular composition stays the same.
  2. The sample forms a new substance with different composition and properties. Correct answer.
  3. The sample changes state from liquid to gas upon heating.
  4. The sample is dissolved in water and later recovered by evaporation.

Explanation

A chemical change produces one or more new substances whose composition and properties differ from the original material. Changes of shape, state, or temporary dissolution leave molecular identity intact and are physical.

Question 42Matter and Its Changes

A sealed rigid container holds a gas at constant temperature. According to the kinetic molecular theory, what happens to the average kinetic energy of the gas particles when the volume is halved?

  1. It doubles because the particles collide more often.
  2. It increases because the pressure increases.
  3. It remains the same because temperature is unchanged. Correct answer.
  4. It decreases by half because the particles have less space.

Explanation

For an ideal gas, average kinetic energy depends only on absolute temperature, not on volume or pressure. Halving the volume raises collision frequency and pressure, but the average kinetic energy stays constant at fixed temperature.

Question 43Matter and Its Changes

Which of the following is a homogeneous mixture?

  1. A mixture of iron filings and sulfur powder
  2. A suspension of sand in water
  3. A glass of salt water with no visible particles Correct answer.
  4. A piece of granite showing distinct mineral grains

Explanation

A homogeneous mixture has a uniform composition throughout a single phase, as in dissolved salt in water. The other samples show distinguishable phases or separable components.

Question 44Matter and Its Changes

A 25.0 mL sample of an unknown metal has a mass of 67.5 g. What is the density of the metal?

  1. 1.69 g/mL
  2. 2.70 g/mL Correct answer.
  3. 0.370 g/mL
  4. 42.5 g/mL

Explanation

Density equals mass divided by volume, so 67.5 g divided by 25.0 mL gives 2.70 g/mL. The result carries three significant figures, matching the given data.

Question 45Matter and Its Changes

A sample of matter is found to contain only one type of atom. How should this sample be classified?

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

Explanation

An element consists of only one kind of atom and cannot be decomposed into simpler substances by chemical means. Compounds contain two or more elements chemically combined, and mixtures contain multiple substances.

Question 46Matter and Its Changes

Which observation most directly indicates that a chemical reaction has occurred?

  1. A liquid becomes more viscous as it cools.
  2. A solid dissolves and the solution becomes clear.
  3. Bubbles form when a solution is heated to its boiling point.
  4. A new odor appears and a precipitate forms when two clear solutions are mixed. Correct answer.

Explanation

Formation of a precipitate together with a new odor indicates new products with different properties, which is evidence of a chemical reaction. Dissolving, boiling, and viscosity changes are physical processes.

Question 47Matter and Its Changes

Which set of coefficients correctly balances the equation __C3H8 + __O2 → __CO2 + __H2O?

  1. 1, 5, 3, 4 Correct answer.
  2. 1, 4, 3, 4
  3. 1, 3, 3, 4
  4. 2, 5, 6, 4

Explanation

Balancing requires 3 carbons, 8 hydrogens, and 10 oxygens on each side, giving C3H8 + 5O2 → 3CO2 + 4H2O. Checking each element confirms 3 C, 8 H, and 10 O on both sides.

Question 48Matter and Its Changes

Which particle-level description best represents a solid ionic compound such as sodium chloride?

  1. A random arrangement of neutral atoms sharing electrons
  2. Discrete molecules held together by weak dispersion forces
  3. Mobile ions that move freely throughout the sample
  4. A lattice of alternating cations and anions held by electrostatic attraction Correct answer.

Explanation

Ionic solids consist of a repeating three-dimensional lattice of cations and anions held together by strong electrostatic attractions. This structure explains their high melting points and their conductivity only when molten or dissolved.

Question 49Matter and Its Changes

A fixed mass of gas occupies 300 mL at 300 K. If the pressure is held constant and the temperature is raised to 600 K, what volume does the gas occupy?

  1. 450 mL
  2. 300 mL
  3. 600 mL Correct answer.
  4. 150 mL

Explanation

Charles's law states that volume is directly proportional to absolute temperature at constant pressure, so V2 = V1(T2/T1). Substituting gives 300 mL × (600 K / 300 K) = 600 mL.

Question 50Matter and Its Changes

Which change in conditions would increase the solubility of a gas such as carbon dioxide in water?

  1. Decreasing the pressure of the gas above the liquid
  2. Stirring the solution vigorously
  3. Increasing the partial pressure of the gas above the liquid Correct answer.
  4. Raising the temperature of the water

Explanation

Henry's law states that gas solubility is directly proportional to the partial pressure of that gas above the liquid. Increasing pressure pushes more gas molecules into solution.