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Understanding IB Chemistry command terms is crucial for success in the course, as these terms determine the type of responses required on your exams. In this post, we will break down these command terms, giving you the knowledge needed to meet IB Chemistry expectations and achieve top marks on your exams!
IB Chemistry Command Terms
Classify – Arrange or order by class or category. For example, if you were asked to classify elements, you would group them according to their properties, such as metals, non-metals, and metalloids, ensuring that each element is placed in the correct category based on its defining features.
Define – Give the precise meaning of a word, phrase, concept or physical quantity. For instance, if you were asked to define "mole," you would state that it is the amount of substance containing as many elementary entities (such as atoms, molecules, electrons, photons, or ions) as there are atoms in 12 grams of carbon-12, which is approximately entities.
Draw – Represent by means of a labelled, accurate diagram or graph, using a pencil. A ruler (straight edge) should be used for straight lines. Diagrams should be drawn to scale. Graphs should have points correctly plotted (if appropriate) and joined in a straight line or smooth curve. For example, if you were asked to draw a Lewis structure of a water molecule, you would illustrate the oxygen atom bonded to two hydrogen atoms, accurately depicting the lone pairs of electrons on the oxygen atom and labeling each element, bond, and lone pair accordingly.
Label – Add labels to a diagram. For example, if you were asked to label a diagram of an electrochemical cell, you would identify and mark key components such as the anode, cathode, salt bridge, electrolyte solutions, and the direction of electron flow.
List – Give a sequence of brief answers with no explanation. For example, if you were asked to list the first three noble gases, you would simply write: helium, neon, argon.
Measure – Obtain a value for a quantity. For instance, if you were asked to measure the concentration of a solution in a given problem, you would calculate the concentration based on provided data and equations, such as using the formula where is concentration, is the amount of substance, and is the volume of the solution.
State – Give a specific name, value or other brief answer without explanation or calculation. For example, if you were asked to state the atomic number of carbon, you would simply write ''6''.
Annotate – Add brief notes to a diagram or graph. For instance, if you were given a diagram of a galvanic cell, you would identify the anode, cathode, salt bridge, direction of electron flow, and the type of electrode reactions occurring at each electrode, along with brief explanations.
Apply – Use an idea, equation, principle, theory or law in relation to a given problem or issue. For example, if you are asked to determine the molar mass of a gas using the ideal gas law, you would apply the equation to solve for and then calculate the molar mass from the given mass and volume of the gas.
Calculate – Obtain a numerical answer showing the relevant stages in the working. For instance, if you are asked to calculate the total heat energy released when 5 grams of a substance with a heat of combustion of 30 kJ/g is burned, you would use the formula how each step: , and then provide the final answer of 150 kJ.
Describe – Give a detailed account. For example, if you are asked to describe the process of fractional distillation, you would explain that it involves heating a mixture to separate its components based on their different boiling points. You would detail how the mixture is heated in a distillation column, how the vapor rises through the column and condenses at different levels, and how the separated components are collected as distinct fractions.
Distinguish – Make clear the differences between two or more concepts or items. For example, if you are asked to distinguish between ionic and covalent bonds, you would explain that ionic bonds involve the transfer of electrons from one atom to another, leading to the formation of positive and negative ions, while covalent bonds involve the sharing of electrons between atoms to achieve stable electron configurations. You would highlight differences such as the types of elements involved, bond strength, and physical properties.
Estimate – Obtain an approximate value. For example, if you are asked to estimate the volume of a gas in a container given the approximate temperature and pressure using the ideal gas law, you would make a rough calculation by substituting approximate values into the equation , and then provide an approximate answer without precise measurements, such as estimating the volume to be around 2 liters.
Formulate – Express precisely and systematically the relevant concept(s) or argument(s). For instance, if you are asked to formulate the general equation for a neutralization reaction between an acid and a base, you would write it as: "An acid reacts with a base to produce a salt and water.".
Identify – Provide an answer from a number of possibilities. For example, if you are asked to identify the type of intermolecular force present in a given substance, such as water, you would select and provide the answer "hydrogen bonding".
Outline – Give a brief account or summary. For example, if you are asked to outline the process of titration, you would provide a summary such as: "1. Add a known volume of the solution with unknown concentration to a flask. 2. Add a few drops of an appropriate indicator. 3. Slowly add a titrant of known concentration from a burette until the indicator changes color, signifying the endpoint. 4. Calculate the concentration of the unknown solution using the volume of titrant used and its concentration.''.
Analyse – Break down in order to bring out the essential elements or structure. For instance, if you are asked to analyze the reaction mechanism of a specific organic reaction, such as the nucleophilic substitution of an alkyl halide, you would break it down by identifying the reactants, detailing the steps of the mechanism (including the nucleophile attack, formation of an intermediate, and the departure of the leaving group), and explaining how each step contributes to the overall reaction.
Comment – Give a judgment based on a given statement or result of a calculation. For example, if you are provided with the result of a pH calculation indicating a value of 3, you would comment that the solution is acidic, with a high concentration of hydrogen ions, and you might also note the implications for the solution’s reactivity or suitability for certain applications.
Compare – Give an account of the similarities between two (or more) items or situations, referring to both (all) of them throughout. For example, if you are asked to compare ionic and covalent bonds, you would describe how both types of bonds involve the interaction between atoms to achieve a stable electron configuration, how both ionic and covalent bonds result in the formation of compounds with specific properties and contribute to the creation of molecules or ionic structures that exhibit distinct chemical behaviors, etc.
Compare and contrast – Give an account of similarities and differences between two (or more) items or situations, referring to both (all) of them throughout. In this type of question you would also focus on the differences. You would for instance state how ionic bonds result from the transfer of electrons from one atom to another, while covalent bonds involve the sharing of electrons between atoms to achieve a stable electron configuration, how ionic bonds generally occur between metals and nonmetals, whereas covalent bonds usually form between nonmetals, etc.
Construct – Display information in a diagrammatic or logical form. For example, if you are asked to construct a Lewis dot structure for a molecule, such as carbon dioxide (CO₂), you would draw the molecule, showing the carbon atom in the center with double bonds connecting to each of the two oxygen atoms, and include the lone pairs of electrons around the oxygen atoms.
Deduce – Reach a conclusion from the information given. For example, if you are provided with data showing that a solution turns blue litmus paper red and has a pH value of 2, you would deduce that the solution is strongly acidic.
Demonstrate – Make clear by reasoning or evidence, illustrating with examples or practical application. For example, if you are asked to demonstrate how a catalyst affects a chemical reaction, you would explain that a catalyst lowers the activation energy needed for the reaction to proceed. You could illustrate this by providing a specific example.
Derive – Manipulate a mathematical relationship to give a new equation or relationship. For instance, if you are asked to derive the formula for calculating the final concentration of a solution after dilution, you start with the concept that the amount of solute before and after dilution remains constant. Given the initial concentration and the initial volume , and the final volume , you would derive the formula where is the final concentration.
Design – Produce a plan, simulation or model. For example, if you are asked to design an experiment to determine the rate of a chemical reaction, you would produce a plan that includes the selection of appropriate reactants, the measurement of their concentrations, the setup of reaction conditions (such as temperature and pressure), and the method for recording the rate of reaction (such as measuring the volume of gas produced or the change in concentration over time).
Determine – Obtain the only possible answer. For example, if you are given the atomic mass of carbon as 12 atomic mass units (amu) and asked to determine the mass of one mole of carbon atoms, you would calculate that the mass of one mole of carbon atoms is 12 grams.
Discuss – Offer a considered and balanced review that includes a range of arguments, factors or hypotheses. Opinions or conclusions should be presented clearly and supported by appropriate evidence. For instance, if you are asked to discuss the effects of catalysts on the rate of chemical reactions, you would review how catalysts lower the activation energy, thereby increasing the reaction rate. You would explore different types of catalysts, such as heterogeneous (solid catalysts in liquid reactions) and homogeneous (catalysts in the same phase as the reactants), and their applications in industrial processes. Additionally, you would consider the limitations and potential deactivation of catalysts, such as poisoning or fouling.
Evaluate – Make an appraisal by weighing up the strengths and limitations. For example, if you are asked to evaluate the use of paper chromatography for separating mixtures of dyes, you would discuss its strengths, such as its simplicity and effectiveness in separating compounds based on their affinity for the stationary and mobile phases. You would also mention its limitations, like its lower resolution compared to other methods and the need for a reference sample for comparison.
Examine – Consider an argument or concept in a way that uncovers the assumptions an interrelationships of the issue. For example, if you are asked to examine the concept of equilibrium in a chemical reaction, you would explore the assumptions that the forward and reverse reactions occur at the same rate and that the concentrations of reactants and products remain constant over time. You would also investigate how changes in conditions, such as temperature or pressure, affect the position of equilibrium, and how these changes interrelate with the reaction dynamics according to Le Chatelier's Principle.
Explain – Give a detailed account including reasons or causes. For example, if you are asked to explain why the boiling point of water is higher than that of ethanol, you would provide a detailed account by discussing the intermolecular forces involved. You would explain that water has strong hydrogen bonding between its molecules, which requires more energy to overcome, resulting in a higher boiling point. In contrast, ethanol, while also capable of hydrogen bonding, has weaker overall intermolecular forces and thus boils at a lower temperature.
Explore – Undertake a systematic process of discovery. For example, if you are asked to explore the factors affecting the equilibrium position of a chemical reaction, you would systematically investigate how changes in concentration, temperature, and pressure impact the equilibrium position. This involves discussing how each factor shifts the equilibrium according to Le Chatelier's Principle and using theoretical principles to predict and explain the changes observed.
Interpret – Use knowledge and understanding to recognise trends and draw conclusions from given information. For instance, if you are given a graph showing the effect of temperature on the rate of a chemical reaction, you would interpret the data by noting that as temperature increases, the reaction rate generally increases. You would draw the conclusion that higher temperatures lead to more frequent and energetic collisions between reactant molecules, thus accelerating the reaction rate.
Justify – Give valid reasons or evidence to support an answer or conclusion. For example, if you are asked to justify why increasing the temperature speeds up the rate of a chemical reaction, you would provide evidence such as the increase in kinetic energy of the reactant molecules, which leads to more frequent and energetic collisions. Additionally, you could reference the Arrhenius equation, which shows that higher temperatures result in a greater proportion of molecules having sufficient energy to overcome the activation energy barrier, thus increasing the reaction rate.
Predict – Give an expected result. For example, if you are asked to predict what will happen when a strong acid is added to a solution of a weak base, you would predict that the weak base will react with the strong acid to form a salt and water, leading to a decrease in the pH of the solution.
Show – Give the steps in a calculation or derivation. For example, if you are asked to show how to calculate the number of moles of gas using the ideal gas law, you would start by identifying the values for pressure, volume, and temperature given in the problem. Next, substitute these values into the ideal gas law equation, , where is pressure, is volume, is the number of moles, is the gas constant, and is temperature. Finally, solve for to determine the number of moles of gas.
Sketch – Represent by means of a diagram or graph (labelled as appropriate). The sketch should give a general idea of the required shape or relationship, and should include relevant features. For instance, if you are asked to sketch the reaction coordinate diagram for an exothermic reaction, you would draw a simple graph with the reaction progress on the x-axis and potential energy on the y-axis. Draw two general curves: one for the reactants and one for the products, showing that the products are at a lower energy level than the reactants. The activation energy barrier should be included. It is important to mention that ''sketch'' questions do not need to be precise or to scale, and a ruler does not have to be used.
Solve – Obtain the answer(s) using algebraic and/or numerical and/or graphical methods. For example, if you are asked to solve for the concentration of a solution after dilution, you would use the formula . Substitute the known values into this equation and solve for the unknown concentration
Suggest – Propose a solution, hypothesis or other possible answer. For example, if you are asked to suggest a method to increase the rate of a chemical reaction, you might propose options such as increasing the temperature, using a catalyst, or raising the concentration of the reactants. Be sure to provide clear justifications for each suggestion, explaining how each method impacts the reaction rate.
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