Acids, bases and salt preparations Flashcards
What does soluble mean?
A substance is able to dissolve in solvent
What does insoluble mean?
A substance is unable to dissolve in solvent
Solubility rules - soluble
1) All common sodium, potassium and ammonium salts
2) All nitrates
3) Most common chlorides
4) Most common sulfates
5) Sodium carbonate, potassium carbonate, ammonium carbonate
6) Sodium hydroxide, potassium hydroxide, ammonium hydroxide
Solubility rules - insoluble
1) Silver chloride, lead chloride
2) Lead sulfate, barium sulfate, calcium sulfate
3) Most common carbonates
4) Most common hydroxides
State the definition of a precipitate
A suspension of particles in a liquid formed when a dissolved substance reacts to form an insoluble substance
State the definition of a salt
The substance formed when the hydrogen ion in an acid is replaced by a metal ion
What is a proton donor?
A proton donor is a substance which gives a hydrogen ion away
What is a proton accepter?
A proton accepter is the substance which receives the hydrogen ion.
Describe acids and bases in terms of proton transfers
A acid is a proton donor and a base is a proton accepter
What is an alkali?
An alkali is a base that is able to dissolve in water
How do you make a soluble salt from a insoluble reactant?
1) Add some dilute hydrochloric acid to a beaker.
2) Add powdered insoluble reactant to some acid in a beaker, one spatula at a time, stirring to mix. The mixture will effervesce. Continue adding powder until some unreacted powder is left over - it is in excess.
3) Filter the mixture in the beaker to remove the excess powder.
4) Allow the water in the solution to evaporate (by heating and/or leaving for a few days) to obtain pure dry crystals of the salt.
Why do you need to add excess of the insoluble reactant?
To make sure all the acid has been reacted/used up
Why do you have to filter the solution?
To separate the unreacted insoluble reactant from the salt solution
What does excess mean?
When there is more than enough of a substance to react with another reactant
How do you make copper sulfate crystals?
1) Place some sulfuric acid in a conical flask and warm it in a water bath.
2) Add a spatula of copper oxide powder to the acid and stir with a glass rod.
3) Continue adding copper oxide powder until it is in excess.
4) Filter the mixture to remove the excess copper oxide.
5) Pour the filtrate (the copper sulfate solution) into an evaporating basin.
6) Heat the copper sulfate solution to evaporate half of the water.
7) Pour the solution into a watch glass and leave to allow all of the water to evaporate.
What colour would the copper sulfate crystals be?
Blue
Why is the sulfuric acid warmed in a water bath?
To speed up the rate of reaction. Warm acid would react faster than cold acid
What is a titre?
A titre is the volume of one reactant needed to react fully with the other reactant in a titration
How do you prepare a soluble salt, starting from an acid and an alkali?
1) Use the pipette and pipette filler to add a measured volume of alkali to a clean conical flask.
2) Add a few drops of indicator and put the conical flask on a white tile.
3) Fill the burette with acid and note the starting volume.
4) Slowly add the acid from the burette to the alkali in the conical flask, swirling to mix.
5) Stop adding the acid when the end-point is reached (when the indicator first permanently changes colour). Note the final volume reading.
6) Repeat steps 1 to 5 until you get concordant titres. 7) More accurate results are obtained if acid is added drop by drop near to the end-point.
What are concordant titres?
Titres within 0.20cm3 of each other
What is the end-point?
The point at which the indicator first permanently changes colour
Why should titration be used in this experiment?
When using an alkali and an acid, you must use titration because there is no insoluble excess reactant that is able to be removed by filtration
How do you prepare an insoluble salt, starting from two soluble reactants?
1) Mix the two salt solutions together in a beaker
2) Stir with a glass rod
3) Filter using filter paper and a funnel
4) Wash with distilled water
5) Dry by leaving in a warm place
Why do you mix the two salt solutions?
In order to form an insoluble salt
Why do you stir the mixture with a glass rod?
To make sure all the reactants have reacted
Why do you wash the precipitate with distilled water?
To remove any other soluble salts
How do you prepare a sample of pure, dry lead(ii) sulfate?
1) Mix similar volumes lead nitrate solution and sodium sulfate solution in a beaker. The precise volumes do not matter since any excess will be removed later.
2) A white precipitate of lead (II) sulfate will form.
3) The reaction mixture is filtered.
4) The residue left on the filter paper is washed with distilled water several times to remove impurities.
5) The residue is then moved to a warm oven to dry.
