Cards (19)

    • pH:

      A measurement that tells you how ACIDIC or ALKALI an aqueous solution is.
      • The pH scale goes from 0-14, and the HIGHER the pH value, the more alkali a solution is.
    • INDICATORs:

      A group of chemical dyes that change colour depending on the pH.
    • WIDE-RANGE INDICATORS:

      Contains a mixture of different dyes, so their colours will slowly change across a wide range of pHs.
      • E.g. universal indicator that can give the following colors:
    • pH PROBES:

      Connected to a pH meter, the pH probe is dipped in the solution to electronically measure the pH & get a numerical reading on the meter.
    • NEUTRALISATION:

      A type of chemical reaction in which an acid & a base react to form water & a salt.
    • neutralisation involves the transfer of H⁺ IONS from the acid to the OH⁻ IONS of the alkali, forming H₂O
    • Sodium hydrogen carbonate cures indigestion by reacting with acid in the stomach, this is neutralisation.
    • Measurements that remove the need for human judgement are more reliable.
    • The probe is more accurate & precise, compared to the indicator is that, as it doesn’t involve humans guessing shades & particular colours.
    • Acid:

      Any substance that forms aqueous solutions with a pH less than 7.
      • Because they ionise (split into their ions) in aqueous solutions to release hydrogen ions (H+), that make the solution acidic.
    • Bases:

      Any substance with a pH greater than 7.
    • Alkalis:

      A subgroup of bases that are soluble in water.
      • So they’re a base that dissolves in water to form a solution with a pH greater than 7. 
      • They form hydroxide ions (OH-) in water.
    • NEUTRAL SOLUTIONS:

      Has a pH of exactly 7, showing a balance between H⁺ & OH⁻ ions.
      • E.g. pure water
    • HCl + NaOH -> NaCl + H2O
      • H+ (from acid) + OH- (from base) -> H2O
      As the acid & base has been neutralised in these sorts of reactions, the pH of the products should be 7 as they’re neutral.
    • Different indicators will change at different pHs.
    • Acids:

      • Hydrochloric (HCl)
      • Sulfuric (H2SO4)
      • Nitric (HNO3)
    • Bases:

      • Sodium hydroxide (NaOH)
      • Calcium carbonate (CaCO3)
    • the ionic equation for the neutralisation of hydrochloric acid with potassium hydroxide
      H+ + OH- -> H2O
    • What is present in the solution at stages 2 & 3 apart from universal indicator & water?
      • at stage 2: sodium ions & chloride ions
      • at stage 2: sodium ions, chloride ions & H+ ions
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