Part 4 Acid and Base Flashcards
What is meant by the term “acid” ?
Acid is a Hydrogen containing substance that dissolves in water and ionises to form H+ ions as the only cation.
What is meant by the term “alkali” ?
Alkali is a substance that dissolves in water and dissociates to give OH- ions as the only anion. // Alkali is a water soluble base that reacts with acid to give salt and water only
What is meant by the term “base” ?
Base is a compound that react with acid to form salt and water only.
What is meant by the term “Strong acid” ?
Strong acid is a hydrogen-containing substance that dissolves in water and completely ionises to give H+ ions as the only cation.
What is meant by the term “weak acid” ?
Weak acid is a hydrogen containing compound that dissoves in water and partially ionises to give H+ ions as the only cation.
What is meant by the term “standard solution” ?
A solution with accurately known concentration
What is meant by the term “basicity” ?
Basicity of an acid is the maximum number of hydrogen ions produced by one molecule of the acid.
State which 3 metal ions will redissolve to become colourless again when excess NaOH is added.
Al3+ , Zn2+, Pb2+
(All 升 le)
(All –> Al)
(升–> Zinc)
(le –> Lead)
State which 3 metal ions will redissolve to become colourless again when excess NH3 is added.
Zn2+, Ag+, Cu2+
State which metal ion will redissolve to become deep blue when excess NH3 is added.
Cu2+
State, if any, the observable change when NaOH is added to Fe2+.
Dirty green precipitate forms
State, if any, the observable change when NaOH is added to Fe3+.
Brown precipitate forms
State, if any, the observable change when NaOH is added to Cu2+.
Pale blue precipitate forms
State, if any, the observable change when NaOH is added to Ag+.
Dark brown precipitate forms
State, if any, the observable change when NH3 is added to Ca2+
No observable change
State, if any, the observable change when NH3 is added to Fe2+.
Dirty green precipitate forms
State, if any, the observable change when NH3 is added to Fe3+.
Brown precipitate forms
State, if any, the observable change when NH3 is added to Cu2+.
Pale blue precipitate forms
State, if any, the observable change when NH3 is added to Ag+.
Dark brown precipitate forms
Suggest a method to compare the strength of acids.
Measure the pH value of the acids ( with the same molarity ). The one with lower pH value is the stronger acid. //
Connect with the same numbers and same types of light bulb, and same voltage of power supply. The bulb with a brighter light is the stronger acid.
(accept other reasonable answer)
Give one application of neutralisation
Soil pH control. //
Fertilizer production
Suggest a chemical that can be used to adjust the soil pH.
CaO,CaCO3, Ca(OH)2, (NH4)2SO4
Suggest why NaOH cannot be used as primary standard.
NaOH can absorb water. // It can react with carbon dioxide in the air. Mass of the pellets cannot be accurately measured.
Suggest why NH3(aq) cannot be used as primary standard.
It is volatile. It would vapourise during preparation, leading to inaccurate measurement of the concentration.
Suggest why conc. H2SO4 cannot be used as primary standard.
It can absorb water vapour from air, leading to inaccurate measurement of the concentration.
Suggest why conc. HCl cannot be used as primary standard.
It is volatile. It would vapourise during preparation, leading to inaccurate measurement of concetration.
Suggest why conc. HNO3 cannot be used as primary standard.
It is volatile and would decompose by light.
Suggest why HNO3 has to be stored in a brown glass bottle.
HNO3 would decompose to give NO2. As the decomposition can be speeded up by light, HNO3 is usually stored in a brown bottle to slow down the decomposition.
Suggest one criteria to be a good primary standard.
High solubility //
Chemically stable //
Involatile and non-toxic //
Does not absorb moisture from the air //
(accept other reasonable answer)
Briefly describe the procedure in preparing standard solution.
Weigh accurately the amount of chemical needed. Dissolve the solid in distilled water. Transfer the solution to a volumetric flask. Make up to the grauation mark with distilled water.
State the liquid(s) that should be used to rinse the volumetric flask.
Distilled water
State the liquid(s) that should be used to rinse the conical flask.
Distilled water
State the liquid(s) that should be used to rinse the pipette.
Distilled water followed by dilute sample.
State the liquid(s) that should be used to rinse the burette
Distilled water followed by dilute sample.
Suggest a suitable indicator for titration between a strong acid and a weak alkali.
Methyl orange.
Suggest a suitable indicator for titration between a weak acid and a strong alkali
Phenolphthalein
