Leah Firmstone
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Quiz am Required Practicals for AQA A Level Chemistry INCOMPLETE, erstellt von Leah Firmstone am 24/04/2017.

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Leah Firmstone
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Required Practicals for AQA A Level Chemistry INCOMPLETE

Frage 1 von 15

1

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

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    beaker
    difference
    known
    minimum
    glass rod
    volumetric flask
    distilled
    graduation line
    funnel
    Invert

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Frage 2 von 15

1

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

Wähle eine der folgenden:

  • Weigh the weighing boat with the solid in it, and then again after the solid has been transferred to a beaker.

  • Invert the volumetric flask before using the solution.

  • Add distilled water to just above the graduation line, then use a dropping pipette to remove the extra.

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Frage 3 von 15

1

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

Wähle eins der folgenden:

  • WAHR
  • FALSCH

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Frage 4 von 15

1

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

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    glass pipette
    indicator
    distilled water
    conical flask
    permanent
    funnel
    air bubbles
    concordant
    burette
    white tile
    rough

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Frage 5 von 15

1

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

Wähle eins der folgenden:

  • WAHR
  • FALSCH

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Frage 6 von 15

1

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

Wähle eine der folgenden:

  • So that any remaining droplets of solution do not fall into the burette and so change the volume/titre value.

  • To stop you knocking it out/it falling out when adjusting the clamp to allow you to read the meniscus.

  • So that it can be used by another group.

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Frage 7 von 15

1

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

Wähle eine der folgenden:

  • Potassium permanganate solution

  • Methyl orange solution

  • Universal indicator solution

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Frage 8 von 15

1

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

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    spirit burner
    calorimeter
    water
    temperature change
    change in mass
    J
    Jmol⁻1
    kJmol-1
    specific heat capacity of water
    energy change

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Frage 9 von 15

1

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

Wähle eine oder mehr der folgenden:

  • Heat is lost to the surroundings, meaning the temperature change is smaller than it should be and so the enthalpy change value is smaller.

  • People make mistakes when doing experiments - the data book values are the values we would get if we always added the correct amount of water etc.

  • Often, experimental values are not calculated under standard conditions.

  • The technique has changed leading to more accurate values, but the data books have not been updated yet.

  • The fuel will sometimes undergo incomplete combustion, meaning that the full amount of energy is not released.

  • Alcohols are very volatile and so some will evaporate from the wick. The value calculated for the number of moles of fuel burnt will be higher than the true value, meaning the value for enthalpy change will be lower than the true value.

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Frage 10 von 15

1

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

Wähle eins der folgenden:

  • WAHR
  • FALSCH

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Frage 11 von 15

1

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

Wähle eine oder mehr der folgenden:

  • Reduce the distance between the flame and the calorimeter

  • Use a glass rod to stir the water/solution in the calorimeter

  • Put a draught screen around the flame

  • Use a larger spirit burner

  • Put a lid on the beaker/calorimeter

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Frage 12 von 15

1

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

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    water
    temperature
    Extrapolate
    mixing
    maximum

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Frage 13 von 15

1

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

Wähle eine der folgenden:

  • To account for the heat lost to the surroundings

  • To eliminate the possibility of anomalous results

  • To find the best temperature at which to carry out the reaction

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Frage 14 von 15

1

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

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    water bath
    conical flask
    temperature
    Accurately
    gas syringe
    volume
    range
    x-axis
    y-axis

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Frage 15 von 15

1

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

Wähle eins der folgenden:

  • WAHR
  • FALSCH

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