Acids & Bases

    Cards (22)

    • what is a Brønsted-Lowry acid?
      a proton donor
    • “half the acid reacts” refers to the half equivalence point
    • the PH at the half equivalence point is the Pka value
    • a base is a proton acceptor
    • Kw= 1 x 10^-14 mol ^2 dm^-6
    • weaker acids dissociate partially, and only a small amount of the acid dissociates, so we can assume that the [HA] = [A-]
    • in pure water, [H+] is equal to [OH-]
    • H2O is not included in the kw expression because H2O only slightly dissociates, so H2O becomes a constant
    • H2O is not included in the kw expression because H2O only slightly dissociates, so H2O becomes a constant
    • why does kw increase as the temperature increases?
      breaking bonds is an endothermic process, so equilibrium shifts to the right to absorb heat, to oppose the increase in temperature
    • what is a weak acid?
      a proton donor that dissociates partially
    • in pure water [H+] = [OH-], so kw= [H+]^2
    • when the endpoint of a titration curve is not vertical, but instead curved, it means that the change in PH is not rapid at the endpoint, an indicator would not change colour rapidly
    • a burette can deliver variable volumes, a pipette is used to accurately measure fixed volumes
    • why is distilled water is used to rinse a conical flask?
      ensures all reagents are able to react
    • when H+ is added, equilibrium shifts to the left
    • how do you ensure that a reading from a PH meter is accurate?
      calibrate the meter with solutions of known PHs, then plot a calibration curve
    • what is meant by a strong acid?
      completely ionises to give H+ in water
    • why is a PH probe washed with distilled water between each calibration measurement?
      so that any residual solutions that may interfere with the reading are washed off
    • to obtain a titration curve:
      • add a fixed volume of an alkali into a beaker
      • add acid in small proportions using a burette
      • stir and use a pH meter to record the pH after each addition of acid
    • why should a pH meter be calibrated before use?
      because after long periods of storage they do not give accurate readings
    • how to make a 250cm3 solution that contains a mass of NaHSO4?
      • weigh an empty weighing boat, add the NaHSO4 and weigh them together, calculate the difference to obtain an accurate mass
      • transfer the solid into a beaker of water to dissolve the NaHSO4
      • transfer the contents into a 250cm3 volumetric flask, making sure to include washings using distilled water
      • make up to the 250cm3 mark and invert, to ensure that the solution is uniform