International A Level (IAL)ChemistryEdexcelFlashcards3. Practical Skills in Chemistry IPhysical Chemistry Core Practicals

Physical Chemistry Core Practicals (Edexcel International A Level (IAL) Chemistry): Flashcards

Exam code: YCH11

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  • What is a gas syringe?

    A gas syringe is a piece of laboratory apparatus used to collect and measure the volume of gas produced in a reaction.

  • Define: molar volume

    Molar volume is the volume occupied by one mole of a gas. At room temperature and pressure, the molar volume of any gas is approximately 24 dm3 mol-1.

  • What are the two methods for collecting a gas produced in a reaction?

    1. Using a gas syringe

    2. Displacement of water

  • What are the key steps in the method to measure the molar volume of CO2 produced from sodium carbonate and hydrochloric acid?

    1. Measure 25.0 cm3 of hydrochloric acid into a conical flask

    2. Add a known mass of sodium carbonate

    3. Immediately connect the gas syringe delivery tube

    4. Allow the reaction to go to completion

    5. Record the volume of carbon dioxide produced

    6. Repeat with different masses of sodium carbonate

  • To convert a volume from cm3 to dm3, divide by ..........

    To convert a volume from cm3 to dm3, divide by 1000.

  • State three assumptions made in the molar volume experiment.

    1. Gas lost before connecting the delivery tube is negligible

    2. The apparatus is airtight so no gas escapes

    3. The reaction goes to completion

  • What is plotted on each axis of the mass-volume graph?

    Mass of sodium carbonate is plotted on the x-axis and volume of carbon dioxide produced is plotted on the y-axis.

  • True or False?

    In the molar volume experiment, gas loss before the syringe is connected is assumed to be negligible.

    True.

    The experiment assumes the amount of gas lost between adding sodium carbonate and connecting the delivery tube is negligible.

  • What is the formula used to calculate the molar volume of a gas from experimental data?

    Molar volume = volume (dm3) ÷ moles. Read the volume from the graph, convert cm3 to dm3 (divide by 1000), then calculate moles from mass ÷ molar mass.

  • What safety precautions should be taken when handling moderately concentrated acids?

    Eye protection and gloves should be worn, as moderately concentrated acids are corrosive.

  • State three assumptions made in a calorimetry experiment.

    1. The specific heat capacity of the solution equals that of water (4.18 J g-1 K-1)

    2. The density of the solution is 1 g cm-3

    3. Heat losses to the surroundings are negligible

  • What is calorimetry?

    Calorimetry is a technique used to measure changes in enthalpy of chemical reactions.

  • What are the steps in the calorimetry method for a displacement reaction in solution?

    1. Place 25 cm3 of copper(II) sulfate solution into a polystyrene cup

    2. Weigh approximately 6 g of zinc powder (excess)

    3. Record temperature every 30 seconds for 2.5 minutes

    4. At 3 minutes, add the zinc powder (do not record temperature at this point)

    5. Continue stirring and record temperature for a further 6 minutes

  • What is a calorimeter?

    A calorimeter is a device used to measure heat transfer in a chemical reaction. It can be made from a polystyrene cup, vacuum flask or metal can.

  • What equation is used to calculate the enthalpy change (ΔH) per mole of limiting reagent?

    ΔH = q ÷ n, where q is the energy transferred (in kJ) and n is the moles of the limiting reagent. A temperature increase indicates an exothermic reaction, giving a negative ΔH.

  • Define specific heat capacity

    Specific heat capacity is the energy required to raise the temperature of 1 g of a substance by 1 K. The specific heat capacity of water is 4.18 J g-1 K-1.

  • Why is a temperature correction graph used in calorimetry?

    A temperature correction graph is used because some reactions are not instantaneous, causing heat loss to the surroundings before the maximum temperature is reached. Extrapolation gives the true maximum temperature change.

  • The equation for calculating energy transferred in a calorimeter is q = ..........ΔT

    The equation for calculating energy transferred in a calorimeter is q = mcΔT.

  • State the three steps to construct a temperature correction graph.

    1. Record temperature before adding reactants for a few minutes to get a steady value

    2. Add the second reactant and continue recording temperature and time

    3. Extrapolate the cooling section of the graph back to the time of addition to find the true maximum temperature

  • True or False?

    In calorimetry calculations, the density of the solution is assumed to be 1 g cm-3.

    True.

    This assumption means the mass of the solution in grams equals its volume in cm3, simplifying the q = mcΔT calculation.

  • State the key steps in performing a titration.

    1. Measure a known volume (20 or 25 cm3) of one solution using a volumetric pipette and place in a conical flask

    2. Place the other solution in the burette (usually filled to 0.00 cm3)

    3. Add a few drops of indicator to the conical flask

    4. Open the burette tap gradually, adding solution portion by portion

    5. Near the end point, add solution dropwise until one drop causes a colour change

    6. Repeat until concordant results are obtained

  • What is a burette?

    A burette is a piece of graduated glassware used to deliver precise, variable volumes of solution in a titration. It is usually marked to a precision of 0.10 cm3.

  • What is the precision and uncertainty of a burette reading?

    A burette is marked to a precision of ±0.10 cm3. The uncertainty of a single reading is ±0.05 cm3, and the uncertainty of a titre (two readings) is ±0.10 cm3.

  • True or False?

    Concordant titration results must be within 0.10 cm3 of each other.

    True.

    Results are considered concordant if they are within 0.10 cm3 of each other. Non-concordant results are discarded before averaging.

  • What is the equivalence point in a titration?

    The equivalence point (also called the end point) is the point in a titration when the two solutions have reacted completely. It is shown by a colour change in the indicator.

  • Why is a white tile placed under the conical flask during a titration?

    A white tile is placed under the conical flask to make the colour change of the indicator easier to see against a pale background.

  • The uncertainty of a titre is .......... cm3, because two burette readings are made.

    The uncertainty of a titre is ±0.10 cm3, because two burette readings are made.

  • What are concordant results?

    Concordant results are titration results that are within 0.10 cm3 of each other. Non-concordant results are discarded, and concordant results are averaged.

  • True or False?

    A burette is always filled to 0.00 cm3 at the start of a titration.

    False.

    The burette is usually filled to 0.00 cm3 at the start of a titration, but this is not a strict requirement. Any starting volume can be used, provided both initial and final readings are recorded.

  • In a titration, 22.80 cm3 of 0.200 mol dm-3 NaHCO3 reacts with HCl in a 1:1 ratio. What is the concentration of the HCl?

    Moles of NaHCO3 = (22.80/1000) × 0.200 = 4.56 × 10-3 mol. Moles of HCl = 4.56 × 10-3 mol (1:1 ratio). Concentration of HCl = 4.56 × 10-3 ÷ (25.0/1000) = 0.182 mol dm-3.

  • Name five pieces of apparatus used in volumetric analysis.

    1. Beaker

    2. Burette

    3. Volumetric pipette

    4. Conical flask

    5. Volumetric flask

  • What is volumetric analysis?

    Volumetric analysis is a process that uses the volume and concentration of one chemical reactant to determine the concentration of an unknown solution. The most common technique is a titration.

  • Why is a three decimal place balance used when preparing a standard solution?

    A three decimal place balance is used to measure mass as precisely as possible, reducing measurement uncertainty and ensuring the concentration of the standard solution is accurate.

  • What is a standard solution?

    A standard solution is a solution of precisely known concentration. It is prepared as accurately as possible using a three decimal place balance and a volumetric flask.

  • State three ways in which concentration can be expressed.

    1. Moles per unit volume (mol dm-3)

    2. Mass per unit volume (g dm-3)

    3. Parts per million (ppm)

  • What is a volumetric flask?

    A volumetric flask is a piece of precise glassware used to prepare a solution of an exact, known volume and concentration.

  • The concentration of a solution is the amount of solute dissolved in a solvent to make .......... of solution.

    The concentration of a solution is the amount of solute dissolved in a solvent to make 1 dm3 of solution.

  • What mass of NaOH is required to prepare 250 cm3 of a 0.200 mol dm-3 solution?

    Moles of NaOH = 0.200 × 0.250 = 0.0500 mol. Molar mass of NaOH = 40.00 g mol-1. Mass = 0.0500 × 40.00 = 2.00 g.

  • What is a volumetric pipette?

    A volumetric pipette is a piece of precise glassware used to measure and transfer an exact, fixed volume of solution into a conical flask during a titration.

  • True or False?

    A concentrated solution contains a high concentration of solute, and a dilute solution contains a low concentration of solute.

    True.

    Concentrated solutions have a high concentration of solute, while dilute solutions have a low concentration. These are comparative terms, not absolute values.

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