IB Chemistry Quiz: Concluding And Evaluating Investigations
20 questions · exam conditions
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Concluding And Evaluating InvestigationsQuestion 1 of 20

A student measures the enthalpy of combustion of ethanol using a simple calorimeter made of a metal can. Their experimental value is significantly less exothermic than the data booklet value. The student concludes that the experiment was a complete failure due to poor execution.

Which statement provides the most valid evaluation of the student's conclusion?

The conclusion is justified, as any percentage error over 20% indicates a failed experiment.
The conclusion is flawed; the difference is likely due to random errors in reading the thermometer, which could be reduced by repeating the experiment.
The conclusion is too strong; a large percentage error is expected due to systematic heat loss to the surroundings, which is an inherent limitation of this experimental setup.
The conclusion is flawed; data booklet values are theoretical and are not expected to match practical results, so no comparison should be made.
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IB Chemistry Quiz

IB Chemistry Quiz: Concluding And Evaluating Investigations

Practice Concluding And Evaluating Investigations in IB Chemistry with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

What this quiz covers

This quiz focuses on Concluding And Evaluating Investigations, giving you a quick way to practice the rules, question types, and explanations that matter most for IB Chemistry.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

All questions

Question 1

A student measures the enthalpy of combustion of ethanol using a simple calorimeter made of a metal can. Their experimental value is significantly less exothermic than the data booklet value. The student concludes that the experiment was a complete failure due to poor execution.

Which statement provides the most valid evaluation of the student's conclusion?

  1. The conclusion is justified, as any percentage error over 20% indicates a failed experiment.
  2. The conclusion is flawed; the difference is likely due to random errors in reading the thermometer, which could be reduced by repeating the experiment.
  3. The conclusion is too strong; a large percentage error is expected due to systematic heat loss to the surroundings, which is an inherent limitation of this experimental setup. (correct answer)
  4. The conclusion is flawed; data booklet values are theoretical and are not expected to match practical results, so no comparison should be made.
Explanation: Simple calorimetry experiments are known to have poor accuracy due to significant, unavoidable heat loss to the surroundings. This is a systematic error inherent in the design, not necessarily a reflection of poor technique. The measured temperature change will be smaller than the true value, leading to a calculated enthalpy change that is less exothermic. Acknowledging this limitation is a key part of evaluating the experiment.

Question 2

A student investigates the effect of concentration on the rate of reaction between sodium thiosulfate and hydrochloric acid. The student mixes different volumes of a stock sodium thiosulfate solution with a fixed volume of HCl and measures the time taken for the solution to become opaque.

The student did not add water to keep the total volume of the reaction mixture constant for each trial. Why does this omission invalidate the conclusion about the relationship between thiosulfate concentration and rate?

  1. It makes the timing of the reaction less precise, which is a source of random error.
  2. It causes the temperature of the mixture to change unpredictably between trials.
  3. It simultaneously changes the concentration of both sodium thiosulfate and hydrochloric acid. (correct answer)
  4. It changes the amount of thiosulfate ions available, but does not affect the validity of the rate measurement.
Explanation: To investigate the effect of one reactant's concentration on the reaction rate, all other variables that can affect the rate must be kept constant. By changing the volume of the thiosulfate solution without keeping the total volume constant, the student is also changing the concentration of the HCl and any other species in the solution, as they are being diluted to different extents in each trial. This means two variables are changing at once, making it impossible to attribute the change in rate solely to the change in thiosulfate concentration.

Question 3

A student reacts a known mass of magnesium with an excess of hydrochloric acid and collects the hydrogen gas produced. The student obtains an actual yield that is 85% of the theoretical yield and concludes that the magnesium sample was only 85% pure.

Which statement provides the best evaluation of the student's conclusion?

  1. The conclusion is valid, as impurity is the only possible reason for a yield less than 100%.
  2. The conclusion is invalid because the reaction is reversible and did not reach completion.
  3. The conclusion is plausible, but the low yield could also be due to experimental loss of product, such as gas escaping before collection. (correct answer)
  4. The conclusion is invalid, as having an excess of acid ensures the yield will always be 100%.
Explanation: A percentage yield less than 100% can be caused by several factors. While an impure reactant is one possibility, it is not the only one. In gas collection experiments, it is common to lose some product due to leaks in the apparatus or during the initial moments of the reaction before the collection system is sealed. Therefore, one cannot definitively conclude the reactant was impure without ruling out other sources of product loss. The student's conclusion is a possible explanation, but it is not a certainty.

Question 4

A student's investigation into the behaviour of a real gas shows significant deviation from the ideal gas law (PV=nRT) when conducted under conditions of very high pressure.

What is the primary reason for this deviation from ideal behaviour?

  1. At high pressure, the speed of the gas particles increases, leading to non-elastic collisions.
  2. At high pressure, the intermolecular forces between gas particles become negligible.
  3. At high pressure, the volume occupied by the gas particles themselves becomes significant compared to the volume of the container. (correct answer)
  4. At high pressure, the gas particles begin to lose kinetic energy, causing the temperature to drop.
Explanation: The ideal gas law is based on a model that makes two key assumptions: (1) there are no intermolecular forces between particles, and (2) the volume of the particles themselves is negligible compared to the container volume. At very high pressures, the particles are forced close together. The volume of the particles is no longer negligible, and the 'free volume' available for them to move in is less than the container volume. This is the main reason for deviation from the ideal gas law under high pressure.

Question 5

A student measures the initial mass of a crucible as 15.21±0.0115.21 \pm 0.01 g and the final mass of the crucible with a sample as 17.73±0.0117.73 \pm 0.01 g.

What is the mass of the sample, including its absolute uncertainty?

  1. 2.520±0.0052.520 \pm 0.005 g
  2. 2.52±0.012.52 \pm 0.01 g
  3. 2.52±0.002.52 \pm 0.00 g
  4. 2.52±0.022.52 \pm 0.02 g (correct answer)
Explanation: The mass of the sample is found by subtracting the initial mass from the final mass: 17.73−15.21=2.5217.73 - 15.21 = 2.52 g. When quantities are added or subtracted, their absolute uncertainties are added. Therefore, the uncertainty in the sample's mass is the sum of the uncertainties of the two measurements: 0.010.01 g + 0.010.01 g = 0.020.02 g. The final result is reported as 2.52±0.022.52 \pm 0.02 g.

Question 6

A student is separating a mixture of ethanol (boiling point: 78 °C) and water (boiling point: 100 °C) via simple distillation. The student collects the first fraction of distillate while the thermometer in the distillation head reads a steady 82 °C. The student concludes that this fraction is pure ethanol.

Which statement best explains why the student's conclusion is incorrect?

  1. The vapor being distilled is a mixture of ethanol and water, so the boiling point is between the boiling points of the two pure substances. (correct answer)
  2. The distillate is an azeotrope, a mixture with a constant boiling point that is different from its components.
  3. The thermometer must be faulty, as the temperature should have been exactly 78 °C.
  4. Some water must have boiled first because its molecules are lighter than ethanol molecules.
Explanation: When a mixture of two miscible liquids is boiled, the vapor produced contains both components. The boiling point of the mixture will be at a temperature between the boiling points of the pure substances. A temperature of 82 °C indicates that a mixture is boiling. Therefore, the vapor being condensed to form the distillate is also a mixture, although it will be enriched in the more volatile component (ethanol). Pure ethanol would only be collected if the distillation temperature was constant at 78 °C, which requires a more efficient separation method like fractional distillation.

Question 7

A chemical synthesis has a percentage yield of 90% but an atom economy of only 30%. A student concludes that the process is highly efficient because the yield is high.

Why is the student's conclusion about the efficiency of the process misleading?

  1. The conclusion is correct; percentage yield is the sole metric for chemical process efficiency.
  2. The low atom economy indicates that 70% of the reactant atoms are converted into unwanted by-products, making the process inherently wasteful. (correct answer)
  3. The efficiency should be calculated as the average of the yield and atom economy, which is (90+30)/2 = 60%.
  4. A 90% yield is not high enough to be considered efficient for an industrial process.
Explanation: The efficiency of a chemical process is evaluated by multiple metrics, including percentage yield and atom economy. Percentage yield describes how effectively reactants are converted to products, accounting for losses. Atom economy describes how many of the atoms from the reactants end up in the desired product versus in waste by-products. A low atom economy of 30% means that 70% of the mass of the reactants is converted into waste. Even with a high yield, such a process is not considered efficient from a green chemistry perspective because it generates a large amount of waste.

Question 8

A student performs a flame test on a sample of potassium chloride (KCl) and observes a lilac flame. They then test a mixture of KCl and sodium chloride (NaCl) and observe only an intense yellow-orange flame. They conclude the mixture contains no potassium.

What is the primary flaw in the student's conclusion?

  1. The conclusion is invalid because chloride ions also produce a distinct color in the flame.
  2. The conclusion is not supported because the bright yellow-orange emission from sodium is known to mask the much fainter lilac color from potassium. (correct answer)
  3. The conclusion is correct; in a mixture, only the element with the lower first ionization energy will show a flame color.
  4. The conclusion is invalid because the two salts react in the flame to produce a new substance with a different flame color.
Explanation: This is a known limitation of qualitative flame tests. The atomic emission from sodium is exceptionally intense and falls in a region of the visible spectrum to which the human eye is very sensitive. The emission from potassium is much less intense. When both are present, the bright sodium color can completely overwhelm or 'mask' the potassium color, leading to a false negative conclusion for potassium. To overcome this, one can view the flame through a cobalt blue glass, which absorbs yellow light and allows the lilac potassium flame to be seen.

Question 9

In a paper chromatography experiment, a student calculates the R_f values for two separated substances. The student concludes that the substance with the higher R_f value has a stronger adsorption to the stationary phase.

Why is the student's conclusion incorrect?

  1. A higher R_f value indicates a greater distance travelled up the paper, which means the substance is more soluble in the mobile phase and has weaker adsorption to the stationary phase. (correct answer)
  2. A higher R_f value indicates a lower solubility in the mobile phase, which means it must have stronger adsorption to the stationary phase.
  3. The R_f value is only related to the molar mass of the substance, not its adsorption properties.
  4. The R_f value is determined by the distance the solvent travels, and is independent of the properties of the separated substances.
Explanation: The R_f value is the ratio of the distance travelled by the substance to the distance travelled by the solvent front. A higher R_f value means the substance travelled further up the paper. This occurs when the substance has a higher affinity for (is more soluble in) the mobile phase and a lower affinity for (is more weakly adsorbed to) the stationary phase. Therefore, the student's conclusion has inverted the relationship.

Question 10

A student is performing a gravimetric analysis to determine the sulfate content of a fertilizer. They precipitate the sulfate as BaSO₄, filter it, and weigh the dry precipitate. The student's final calculated percentage of sulfate is higher than the expected value.

Which procedural error would most likely lead to a systematically high result?

  1. Some of the precipitate was lost during transfer from the beaker to the filter funnel.
  2. The precipitate was not dried to a constant mass and was still slightly wet when weighed. (correct answer)
  3. The initial mass of the fertilizer sample was accidentally recorded as being higher than it actually was.
  4. Not enough BaCl₂ solution was added to precipitate all of the sulfate ions.
Explanation: A high result for the percentage of sulfate means the measured mass of the BaSO₄ precipitate was artificially high. If the precipitate was not dried completely, the residual water would add to its mass. This would lead to a larger calculated mass of sulfate, and consequently a higher percentage of sulfate in the original sample. All other options would lead to a systematically low result: losing precipitate (A) decreases the final mass, overestimating the initial sample mass (C) increases the denominator in the percentage calculation, and incomplete precipitation (D) results in less precipitate being formed.

Question 11

A student determines the concentration of an HCl solution by titrating it against a standard NaOH solution. For every trial, the student consistently reads the volume from the top of the burette meniscus instead of the bottom. The student observes that their repeated titration values are very close to one another.

How would this procedural error affect the calculated concentration of HCl and the precision of the results?

  1. The calculated concentration will be systematically lower than the true value, and the precision will be low.
  2. The calculated concentration will be systematically higher than the true value, but the precision may remain high.
  3. The calculated concentration will be systematically lower than the true value, but the precision may remain high. (correct answer)
  4. The calculated concentration will be randomly affected, and the precision will be low.
Explanation: Reading from the top of the meniscus consistently makes the recorded volume of NaOH smaller than the actual volume delivered. A smaller volume of NaOH used in the calculation (n = CV) leads to a smaller calculated number of moles of HCl, resulting in a systematically lower concentration. Since the error is consistent across all trials, the results can still be precise (values are close to each other), even though they are inaccurate.

Question 12

In an experiment to determine the molar mass of a gas using the ideal gas equation, PV=nRTPV=nRT, a student obtains an experimental value of 32.5 g mol⁻¹. The gas is known to be carbon dioxide (CO₂). The relative atomic masses are C=12.01, O=16.00.

The theoretical molar mass of CO₂ is 44.01 g mol⁻¹. Which experimental error most likely accounts for the student's result being systematically low?

  1. The measured mass of the gas was higher than the actual mass.
  2. The measured temperature of the gas was higher than its actual temperature.
  3. Some air leaked into the gas syringe, mixing with the carbon dioxide. (correct answer)
  4. The measured volume of the gas was lower than the actual volume.
Explanation: Molar Mass = mRT/PV. A low calculated molar mass means the value of mRT/PV is too low. Air is a mixture of mostly N₂ (M≈28 g mol⁻¹) and O₂ (M≈32 g mol⁻¹), with an average molar mass of approximately 29 g mol⁻¹. If air leaked into the syringe, the total number of moles of gas (n) would increase, but the measured mass (m) would be only that of the CO₂ (or the mass change of the generating flask). A more direct way to think is that the collected gas is a mixture with a lower average molar mass than pure CO₂, which would lead to a low result. Let's analyze other options. B: If T measured is too high, M would be too high. C: If air leaks in, the volume V will be larger than the volume of just CO₂. n = PV/RT. If V is too high, n is calculated to be too high. M = m/n. If n is too high, M will be too low. This is the correct answer. A: Higher mass would lead to a higher M. D: Lower volume would lead to a lower n, and a higher M.

Question 13

A student aims to measure the enthalpy of neutralization by mixing 50.0 cm³ of 1.00 mol dm⁻³ HCl and 50.0 cm³ of 1.00 mol dm⁻³ NaOH in a thin-walled glass beaker. They record the initial and final temperatures to calculate the enthalpy change.

Which modification would lead to the most significant improvement in the accuracy of the experimental result?

  1. Using 100.0 cm³ of each solution to generate more heat.
  2. Replacing the glass beaker with a polystyrene foam cup. (correct answer)
  3. Using a digital thermometer with a precision of ±0.01 °C instead of ±0.1 °C.
  4. Measuring the solution volumes with a 50.00 cm³ pipette instead of a 50 cm³ measuring cylinder.
Explanation: The largest source of systematic error in simple calorimetry experiments is heat loss to the surroundings. A thin-walled glass beaker is a poor insulator. Replacing it with a polystyrene foam cup, which is a much better insulator, would significantly reduce heat loss and therefore make the measured temperature change closer to the true value, improving accuracy. While the other options would improve precision (D, C) or increase the magnitude of the temperature change (A), minimizing the primary systematic error (heat loss) is the most critical improvement.

Question 14

A student calculates the enthalpy of combustion of methane using average bond enthalpies from the data booklet and gets a value of –808 kJ mol⁻¹. The accepted literature value for the standard enthalpy of combustion is –890 kJ mol⁻¹.

What is the most significant and specific reason for the discrepancy between the calculated value and the literature value?

  1. Average bond enthalpies are derived from a wide range of compounds and do not represent the exact bond energies in methane and its products.
  2. The standard enthalpy of combustion refers to products in their standard states (e.g., H₂O(l)), while bond enthalpy calculations are for species in the gaseous state (e.g., H₂O(g)). (correct answer)
  3. Experimental determination of the standard enthalpy of combustion is prone to systematic errors, making the literature value unreliable.
  4. The calculation using bond enthalpies does not account for the activation energy of the reaction.
Explanation: Both A and B are valid reasons for a discrepancy, but B identifies a more specific and quantifiable source of error. Standard enthalpy of combustion (ΔH⦵c) is defined with all substances in their standard states. For the combustion of methane, the product water is in the liquid state, H₂O(l). Bond enthalpies are defined as the energy to break one mole of bonds in the gaseous state. Therefore, a calculation using bond enthalpies determines the enthalpy change for the reaction forming gaseous water, H₂O(g). The difference between the two values is largely due to the enthalpy of vaporization of water, which is not accounted for in the bond enthalpy calculation.

Question 15

An experiment is designed to measure how the rate of CO₂ production changes when the temperature is varied in the reaction between CaCO₃ and excess HCl.

To ensure that temperature is the only variable affecting the rate, which condition is most critical to keep constant across all trials?

  1. The concentration and volume of the HCl solution. (correct answer)
  2. The duration of each experimental trial.
  3. The total volume of CO₂ collected.
  4. The time taken for the reaction to go to completion.
Explanation: To conduct a fair test on the effect of temperature, all other factors that could influence the reaction rate must be controlled. The rate of this reaction also depends on the concentration of the acid and the surface area of the solid. Since the acid is specified as being in excess, its concentration will not be the limiting factor, but it must be the same at the start of each trial to allow for a valid comparison. Similarly, the volume of acid and mass/surface area of CaCO₃ must be kept constant. Of the choices given, keeping the concentration and volume of HCl constant is a critical control variable.

Question 16

A student performs four titrations to find the concentration of an unknown acid and obtains the following titres: 21.55 cm³, 21.60 cm³, 21.50 cm³, and 21.55 cm³. The actual, certified concentration of the acid corresponds to a theoretical titre of 22.50 cm³.

Which statement best describes the student's results?

  1. The results are accurate but not precise.
  2. The results are both accurate and precise.
  3. The results are neither accurate nor precise.
  4. The results are precise but not accurate. (correct answer)
Explanation: Precision refers to how close a series of measurements are to one another. The student's titres range from 21.50 cm³ to 21.60 cm³, a very small range of 0.10 cm³. This indicates high precision. Accuracy refers to how close the measurements are to the true or accepted value. The average titre is approximately 21.55 cm³, which is almost 1.00 cm³ away from the true value of 22.50 cm³. This is a large discrepancy, indicating low accuracy. The combination of high precision and low accuracy suggests a systematic error in the experiment.

Question 17

In an experiment investigating reaction kinetics, a student collects data at only two different concentrations. They observe that doubling the concentration of reactant A leads to a four-fold increase in the initial rate. The student concludes that the reaction is second order with respect to A.

Which statement represents the most critical evaluation of this conclusion?

  1. The conclusion is fully justified because the data perfectly matches the mathematical relationship for a second-order reaction.
  2. The conclusion is invalid because experimental error could never produce such a perfect relationship.
  3. The conclusion is invalid because the order of reaction can only be determined from the stoichiometry of the balanced chemical equation.
  4. The conclusion is reasonable based on the data, but it lacks reliability as it is based on only two data points, which is insufficient to establish a scientific trend confidently. (correct answer)
Explanation: While the data from the two points suggests a second-order relationship (rate ∝ [A]²), drawing a firm conclusion from only two data points is scientifically weak. A reliable determination of reaction order requires multiple data points (ideally, a graph of rate vs. concentration or log(rate) vs. log[concentration]) to establish a clear trend and to ensure the observation is not a result of coincidence or experimental error. The conclusion is plausible but not robustly supported.

Question 18

An investigation shows that adding a catalyst to a reversible reaction at equilibrium increases the rate of both the forward and reverse reactions. A student concludes that adding a catalyst must therefore increase the final yield of the products.

Why is the student's conclusion incorrect?

  1. A catalyst increases the rates of the forward and reverse reactions equally, so the position of equilibrium and the yield are unchanged. (correct answer)
  2. A catalyst is consumed during the reaction, so its effect on yield is temporary.
  3. A catalyst only increases the rate of the forward reaction, not the reverse reaction.
  4. A catalyst lowers the activation energy, which favours the endothermic direction and may increase or decrease the yield.
Explanation: A catalyst provides an alternative reaction pathway with a lower activation energy. This lower energy barrier applies to both the forward and the reverse reactions. As a result, the rates of both reactions increase by the same factor. The system reaches equilibrium much faster, but the ratio of the rate constants (the equilibrium constant, K) remains unchanged. Therefore, the composition of the mixture at equilibrium, and thus the equilibrium yield, is not affected by the presence of a catalyst.

Question 19

A student performs titrations to determine the concentration of ethanoic acid in vinegar. They obtain the following concentration values from four trials: 0.85 mol dm⁻³, 0.84 mol dm⁻³, 0.68 mol dm⁻³, 0.86 mol dm⁻³.

What is the most appropriate action to take when processing these results to find the average concentration?

  1. Average all four values to ensure that all data collected is used in the final result.
  2. Discard the 0.68 mol dm⁻³ result as an outlier and average the other three concordant values.
  3. Use the median value (0.845 mol dm⁻³) as it is less affected by outliers than the mean.
  4. Perform more trials to determine if the 0.68 mol dm⁻³ result is anomalous before deciding to exclude it. (correct answer)
Explanation: Good scientific practice requires a justification for excluding data. The value 0.68 mol dm⁻³ appears to be an outlier compared to the other three values, which are closely clustered (concordant). However, discarding a data point without further evidence is not rigorous. The best course of action is to perform additional trials. If subsequent results are consistent with the 0.84-0.86 range, this provides strong evidence that the 0.68 value was anomalous (due to a one-off error) and can be excluded. If further low values appear, it might indicate an issue with the procedure.

Question 20

A student's experiment to determine the enthalpy of neutralization gave a result of -52.8 kJ/mol, while the literature value is -57.3 kJ/mol. The student calculated a percentage error of 7.9%. Which evaluation of the experimental reliability is most appropriate?

  1. The result demonstrates good accuracy since the percentage error is less than 10%, indicating the experimental method was reliable
  2. The result shows acceptable precision but questionable accuracy, requiring analysis of systematic errors in the experimental procedure
  3. The percentage error calculation confirms the result is within acceptable limits, validating both the experimental design and execution
  4. The negative deviation from the literature value indicates heat loss to surroundings, confirming expected systematic error direction (correct answer)
Explanation: Option D correctly evaluates both the magnitude and direction of error, recognizing that the less negative result indicates heat loss (a predictable systematic error in calorimetry). Option A focuses only on magnitude. Option B incorrectly discusses precision without precision data. Option C overstates what percentage error alone can validate.