Required Practicals for AQA A Level Chemistry INCOMPLETE

Making up a standard solution Stage 1: transferring a [blank_start]known[blank_end] mass of the solid • Weigh the solid into a weighing boat recording the mass (to appropriate precision). • Transfer the solid to a [blank_start]beaker[blank_end]. • Re-weigh the weighing boat and record the [blank_start]difference[blank_end] in mass. Stage 2: dissolving the solid in distilled water • Add the [blank_start]minimum[blank_end] distilled water to the beaker to dissolve. • Stir the beaker with the [blank_start]glass rod[blank_end] until the solid has dissolved. Stage 3: rinsing all glassware and making up the solution • Transfer the solution to a [blank_start]volumetric flask[blank_end] using a funnel. • Rinse all used glassware into the volumetric flask (glass rod, beaker and [blank_start]funnel[blank_end]). • Add [blank_start]distilled[blank_end] water up to the [blank_start]graduation line[blank_end] (on the volumetric flask). • [blank_start]Invert[blank_end] the flask several times.

Which of the following should you NOT do when making up a standard solution?

Any glassware that has been in contact with the solution should be rinsed into the volumetric flask when making up a standard solution.

Carrying out an acid-base titration Stage 1: Preparing the conical flask • Using a [blank_start]glass pipette[blank_end], transfer the desired amount of the acidic solution into the conical flask. • Add several drops of an appropriate [blank_start]indicator[blank_end] to the conical flask. • Rinse any solution on the sides of the flask into the flask with [blank_start]distilled water[blank_end]. Stage 2: preparing the burette • Fill the burette up with the basic solution using a [blank_start]funnel[blank_end]. • Run the solution through the jet, ensuring that there are no [blank_start]air bubbles[blank_end] present. • Remove the funnel from the burette. Stage 3: performing the titration • Place the conical flask on a [blank_start]white tile[blank_end] beneath the burette. • Record the starting volume of the burette. • Titrate the solution, swirling the [blank_start]conical flask[blank_end] until a [blank_start]permanent[blank_end] colour change is observed. • Record the end volume in the [blank_start]burette[blank_end] and calculate the titre. • Repeat until [blank_start]concordant[blank_end] results (titre values within 0.1 cm³ of each other) are achieved and calculate a mean titre (never include [blank_start]rough[blank_end] values).

Using distilled water to rinse the sides of the conical flask in an acid-base titration will negatively affect your results.

Why do you remove the funnel from the burette during a titration?

Which of the following is NOT a suitable indicator for use in ANY titration?

Experimentally finding the enthalpy change of combustion Stage 1: preparing the chemicals • Add the fuel to the [blank_start]spirit burner[blank_end] and record the initial mass. • Add a known quantity of water to the [blank_start]calorimeter[blank_end] and clamp in position above the spirit burner. • Use thermometer to measure the initial temperature of the [blank_start]water[blank_end]. Stage 2: carrying out the experiment • Use the spirit burner to heat water in the calorimeter to roughly (40ᵒC) and record the [blank_start]temperature change[blank_end]. • Reweigh the spirit burner and calculate the [blank_start]change in mass[blank_end] of the fuel. Stage 3: interpreting the results • Calculate the energy released ([blank_start]J[blank_end]) using the equation q = mcΔT where q = [blank_start]energy change[blank_end]; m = mass of water heated; c = [blank_start]specific heat capacity of water[blank_end] (4.18); ΔT = change in temperature. • Calculate the enthalpy change ([blank_start]Jmol⁻1[blank_end]) using the equation ΔH = q / (moles of fuel). • Convert into [blank_start]kJmol-1[blank_end] by dividing your answer by 1000.

Why are data book values often higher than those calculated experimentally? (CHOOSE 4)

It is important to use a very precise thermometer when calculating the enthalpy change of a reaction.

Which of the following are ways in which the calorimetry method can be improved to minimise heat loss? CHOOSE 3

Experimentally finding the enthalpy change of a reaction, accounting for heat loss Add a (5.00g) sample of solid to (50g) of [blank_start]water[blank_end] and start the stop watch. Record the [blank_start]temperature[blank_end] of the solution every subsequent minute for approximately 5 minutes. Plot a graph of temperature (y-axis) versus time (x-axis). [blank_start]Extrapolate[blank_end] back to the time of [blank_start]mixing[blank_end] (T=0s) to establish the [blank_start]maximum[blank_end] temperature change. Calculate ΔH in kJ mol-1 using the equation: ΔH = (m × c × ∆T)/(n ×1000 )

Why is the line of best fit extrapolated back to the time of mixing when calculating enthalpy change?

Investigate how the rate of reaction changes with temperature 1. Set a [blank_start]water bath[blank_end] to 20ᵒC. 2. Accurately measure out 20cm³ of 1.0 mol dm⁻³ hydrochloric acid and pour into a [blank_start]conical flask[blank_end]. 3. Allow the solution of hydrochloric acid to reach the [blank_start]temperature[blank_end] of the water bath. 4. [blank_start]Accurately[blank_end] weigh out 1.0g of magnesium ribbon. 5. Place the magnesium into the conical flask, immediately attaching the [blank_start]gas syringe[blank_end] and starting a timer. 6. Record the [blank_start]volume[blank_end] of gas evolved in the first 20 seconds. 7. Repeat steps 1 – 6 for a [blank_start]range[blank_end] of temperatures (30ᵒC – 60ᵒC). 8. Plot a graph of temperature ([blank_start]x-axis[blank_end]) versus initial rate (cm³/20s) ([blank_start]y-axis[blank_end]).

It is not possible to accurately measure the effect of temperature on rate of reaction at temperatures above 60ᵒC.