Physical Chemistry Practicals (OCR A Level Chemistry A): Flashcards
Exam code: H432
1/210Still learning
Know0
- FrontMoles Determination
Define molar volume
Was this flashcard helpful?
Cards in this collection (21)
Define molar volume
Molar volume is the volume occupied by one mole of any gas at room temperature and pressure, equal to 24.0 dm3 (or 24 000 cm3).
Define standard solution
A standard solution is a solution of precisely known concentration, prepared using a three-decimal-place balance and a volumetric flask to minimise measurement uncertainties.
Define specific heat capacity
Specific heat capacity is the energy required to raise the temperature of 1 g of a substance by 1 K, with units of J g-1 K-1.
In an experiment where a solid reacts with excess acid and the gas produced is collected by displacement of water, what calculation links the gas volume to the number of moles?
The number of moles of gas is calculated using n = V (dm3) / 24.0, where molar volume is 24.0 dm3 at room temperature and pressure.
In a titration, why is a white tile placed beneath the conical flask?
The white tile provides a contrasting background that makes the colour change of the indicator easier to see, particularly near the end point.
In a calorimetry experiment involving a reaction in solution, what equation is used to calculate the heat energy transferred?
The heat energy transferred is calculated using q = m c ΔT, where m is mass, c is specific heat capacity and ΔT is the temperature change.
When magnesium is burned in a crucible to find the formula of magnesium oxide:
The mass increase equals the mass of .......... that has reacted
Divide each mass by its .......... to get the mole ratio
Use the mole ratio to determine the .......... of the oxide
When magnesium is burned in a crucible to find the formula of magnesium oxide:
The mass increase equals the mass of oxygen that has reacted
Divide each mass by its Mr to get the mole ratio
Use the mole ratio to determine the formula of the oxide
In a titration, the solution of known concentration is placed in the .......... and the solution of unknown concentration is placed in the ...........
In a titration, the solution of known concentration is placed in the burette and the solution of unknown concentration is placed in the conical flask.
True or False?
In a combustion calorimetry experiment, the polystyrene cup is replaced by a copper can and a spirit burner.
True.
A copper can holds the water that is heated by the spirit burner below it. The temperature rise of the water is used to calculate the enthalpy of combustion.
True or False?
When collecting a gas over water by displacement, the bung should be inserted into the flask before adding the acid to prevent gas escaping.
False.
The bung should be inserted immediately after adding the acid. Delaying causes gas to escape and introduces error into the volume measurement.
True or False?
Concordant titration results are within 0.10 cm3 of each other.
True.
Results within 0.10 cm3 are considered concordant and are averaged. Results outside this range are discarded.
In a calorimetry experiment, a temperature correction graph is used when the reaction is not .......... The cooling portion of the graph is .......... back to the time at which the reactants were mixed, to obtain the .......... temperature change.
In a calorimetry experiment, a temperature correction graph is used when the reaction is not instantaneous. The cooling portion of the graph is extrapolated back to the time at which the reactants were mixed, to obtain the true maximum temperature change.
In a gas collection experiment, why is a gas syringe preferred over a measuring cylinder in a water trough for measuring the volume of carbon dioxide?
Carbon dioxide is soluble in water, so measuring it over water gives a lower recorded volume than was actually produced, increasing experimental error.
A burette reading is recorded .......... and .......... each run to obtain the .......... (volume delivered).
A burette reading is recorded before and after each run to obtain the titre (volume delivered).
In a combustion calorimetry experiment, why is the enthalpy of combustion value obtained experimentally usually less exothermic than the standard value?
Heat is lost to the surroundings and some is absorbed by the calorimeter itself. Incomplete combustion of the fuel also reduces the heat transferred to the water.
True or False?
The molar volume of 24.0 dm3 mol-1 applies only at room temperature and pressure (RTP).
True.
At different temperatures or pressures, the ideal gas equation (PV = nRT) must be used instead.
The uncertainty in a single burette reading is ±0.05 cm3. What is the uncertainty in the titre calculated from two burette readings, and why?
The uncertainty in the titre is ±0.10 cm3 because two readings are subtracted, so their uncertainties are added following the rules of propagation of uncertainties.
True or False?
In a Hess's law calorimetry approach, the enthalpy change of a reaction that cannot be measured directly can be determined from two reactions that can be measured.
True.
Using ΔHr = ΔH1 − ΔH2, the indirect enthalpy change is calculated from two measurable enthalpy changes.
True or False?
In a titration, burette readings should be recorded to a precision of ±0.05 cm3.
True.
Burettes are graduated to 0.10 cm3, so readings are recorded to half the smallest division, giving a precision of ±0.05 cm3.
In a calorimetry experiment involving a reaction in solution, what two assumptions are made about the solution itself?
The solution is assumed to have the same specific heat capacity as pure water (4.18 J g-1 K-1) and the same density as pure water (1 g cm-3).
A student prepares a standard solution by dissolving a weighed solid in a beaker, then transfers it to a volumetric flask. What key step must be carried out after the transfer to ensure accuracy?
The beaker must be rinsed several times with distilled water and the washings added to the volumetric flask, ensuring all solute is transferred before making up to the graduation mark.
Sign up to unlock flashcards
or