Preparation of Salts (Cambridge (CIE) IGCSE Co-ordinated Sciences (Double Award): Chemistry): Flashcards
Exam code: 0654 & 0973
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What is a salt, in terms of its formation from an acid?
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What is a salt, in terms of its formation from an acid?
A salt is a compound formed when the hydrogen atom in an acid is replaced by a metal or ammonium ion.
To prepare a soluble salt using an insoluble base, excess base is added to warm acid, then the mixture is ______ to remove unreacted solid before ______ the solution.
To prepare a soluble salt using an insoluble base, excess base is added to warm acid, then the mixture is filtered to remove unreacted solid before crystallising the solution.
True or False?
Titration is the correct method for preparing a soluble salt from an insoluble base.
False.
Titration is used when the base is soluble (an alkali). An insoluble base is added in excess, then filtered off to leave the salt solution.
Why is excess solid reactant used when preparing a soluble salt from a metal or insoluble base?
Excess solid is used to ensure all the acid reacts. The unreacted solid is then removed by filtration, leaving a pure salt solution.
The reaction CuO (s) + H2SO4 (aq) → ______ (aq) + H2O (l) is an example of preparing a soluble salt using an excess insoluble ______.
The reaction CuO (s) + H2SO4 (aq) → CuSO4 (aq) + H2O (l) is an example of preparing a soluble salt using an excess insoluble base.
How do you know when a salt solution is saturated and ready for crystallisation?
A cold glass rod is dipped into the heated solution. If crystals form on the rod, the solution is saturated and ready to crystallise.
Why is indicator not used in the final titration when preparing a soluble salt from a soluble alkali?
Indicator is not used in the final titration because it would contaminate the salt product. The exact volume of acid found in the trial run is used instead.
What is a precipitation reaction, in the context of preparing insoluble salts?
A precipitation reaction is one in which two soluble solutions are mixed to form an insoluble solid product called a precipitate.
True or False?
To prepare an insoluble salt by precipitation, both reactants must be insoluble.
False.
Both reactants must be soluble in water. The insoluble salt forms as a precipitate when the two solutions are mixed.
To prepare an insoluble salt, two soluble salt solutions are ______ together, then the precipitate is removed by ______.
To prepare an insoluble salt, two soluble salt solutions are mixed together, then the precipitate is removed by filtration.
Why is the precipitate washed with distilled water during the preparation of an insoluble salt?
The precipitate is washed with distilled water to remove traces of other dissolved ions from the reactant solutions, giving a pure product.
When Pb(NO3)2 (aq) is mixed with K2SO4 (aq), the insoluble precipitate formed is ______ (s).
When Pb(NO3)2 (aq) is mixed with K2SO4 (aq), the insoluble precipitate formed is PbSO~4~ (s).
What are the four steps in preparing a pure, dry insoluble salt by precipitation?
Mix two soluble salt solutions, filter to collect the precipitate, wash with distilled water to remove impurities, then leave to dry.
Define "hydrated salt".
A hydrated salt is one that contains water molecules within its crystal structure, called water of crystallisation.
True or False?
Anhydrous copper(II) sulfate is blue.
False.
Anhydrous copper(II) sulfate is white. The blue form is hydrated copper(II) sulfate, which contains water of crystallisation.
Heating hydrated copper(II) sulfate drives off ______, forming ______ copper(II) sulfate.
Heating hydrated copper(II) sulfate drives off water, forming anhydrous copper(II) sulfate.
How can anhydrous copper(II) sulfate be converted back to its hydrated form?
Adding water to anhydrous copper(II) sulfate converts it back to hydrated copper(II) sulfate, turning the solid from white to blue.
What does the term "anhydrous" mean when describing a salt?
Anhydrous means that the salt contains no water of crystallisation in its structure.
The chemical formula CuSO4·5H2O represents ______ copper(II) sulfate. The ·5H2O represents ______ molecules of water.
The chemical formula CuSO4·5H2O represents hydrated copper(II) sulfate. The ·5H2O represents five molecules of water.
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