C8 - Acids, bases and salts (Only C8.1 - C8.3) Flashcards
When any substance is dissolved in water it forms an
aqueous solution
Aqueous solutions can be either
acidic, alkaline or neutral
What does an indicator do
tells if a solution is acidic, alkaline, or neutral by changing color
Acids are substances that form
Hydrogen (H+) ions when dissolved in water
A base is any substance that can
neutralize an acid
Acids are proton
donors
Bases are proton
acceptors
Bases can either be
soluble or insoluble in water
Bases that are soluble in water are called
alkalis
Alkalis are substances that release
hydroxide (OH-) ions in aqueous solutions which are typically metal hydroxides
Two main types of insoluble bases are
metal carbonates and metal oxides
All acids ionize (become ions) in aqueous solutions and the strength of the acid is determined by
how much it ionizes water
Characteristics and examples of weak acids
Only partially ionize in water meaning not all acid molecules break up (dissociate) to form H+ ions
Most acids are weak acids
Example: ethanoic acid CH3COOH <==> CH3COO- + H+
Citric acid
Carbonic acid
Characteristics and examples of strong acids
They fully ionize in water meaning all the acid molecules break up (dissociate) to form H+ ions
Example: HCI ==> H+ + Cl-
HNO3 ==> H+ + NO3-
Other strong acids include: sulfuric and nitric acid
When bases neutralize acids they form
salt and water
Characteristics and examples of weak bases
Weak bases don’t fully ionize in aqueous solutions as only a few of the molecules break up (dissociate) to form OH- ions
Example: Ammonia NH3
NH3 + H2O ==> NH4+ + OH-
Characteristics and examples of strong bases
Strong bases full ionize in aqueous solutions meaning all the molecules break up (dissociate) to form OH- ions
Examples of strong bases include:
Potassium hydroxide: KOH ==> K+ + OH-
Sodium hydroxide: NaOH ==> Na+ + OH-
When acids react with metals what is produced
a hydrogen and a salt
Examples of acids + metals
Zinc + sulfuric acid ==> zinc sulfate + hydrogen
Magnesium + hydrochloric acid ==> magnesium chloride + hydrogen
What is a neutralization reaction
when an acid and a base react to form a salt and water
Metal carbonate, metal oxides and metal hydroxides are all
bases
When an acid reacts with metal hydroxides it forms
salt + water
i.e hydrochloric acid + sodium hydroxide ==> sodium chloride + water
When an acid reacts with a metal oxide it forms
salt + water
i.e hydrochloric acid + magnesium oxide ==> magnesium chloride + water
When bases are heated with ammonium salts it gives off
ammonium gas
Base + ammonium salt ==>
salt + ammonia (gas) + water
How can we control soil acidity so that plants can grow properly?
add a suitable base such as slaked lime to soil to neutralize soil acidity to create an optimum pH for the plant to grow in
How to determine whether a substance is an acid or alkali
finding out the pH or using an indicator
What does pH relate to
the concentration of H+ ions
Difference between strength and concentration
Strength of an acid relates to how much an acid can dissociate as concentration relates to how much acid there is in a certain volume
i.e you can have high concentration HCI as well as low concentration HCI (dilute)
The more H+ ions a substance has
the lower the pH gets
Examples of indicators and what color it turns
Methyl orange: Red in acid Yellow in neutral and alkali Litmus paper: Red in acid Violet in neutral Blue in alkali Phenolphthalein: Colorless in acid Pink in alkali
Oxides of elements can be made by
heating the element in air or oxygen
Basic oxides characteristics and examples
Metals form metal oxides which are basic oxides
These oxides dissolve in water to form OH- ions
i.e Magnesium
2Mg + O2 ==> 2MgO
Amphoteric oxides characteristics and examples
They are oxides of less reactive metals like Al2O3, ZnO and PbO
They react with both acids and alkalis to produce salts
Acidic oxides characteristics and examples
Non metals form non metal oxides which are acidic
i.e Sulfur dioxide
Oxides are normally gases and dissolve in water to form mineral acid and release H+ ions
Neutral oxides characteristics and examples
They don’t react with acids or alkalis
i.e Carbon monoxide and water
How to test for insoluble oxides
If they react with HCI they are basic oxides
If they react with NaOH they are acidic oxides
If they react with none of the above they are neutral oxides
Acid(aq) + alkali(aq) ==>
salt(aq) + water(l)
Acid(aq) + base(s) ==>
salt(aq) + water(l)
Acid(aq) + carbonate(s) ==>
salt(aq) + water(l) + carbon dioxide(g)
Acid(aq) + metal(s) ==>
salt(aq) + hydrogen(g)
What are the solubility rules
All common sodium, potassium and ammonium salts are soluble
All nitrates are soluble
Chlorides, bromides and iodides are soluble - except silver chloride, silver bromide and silver iodide
Sulfates are soluble - except barium, lead and calcium
Carbonates are insoluble - except sodium, potassium and ammonium
What experimental techniques are used to produce a pure dry sample of soluble salt from a soluble base, carbonate or metal.
Apparatus: heatproof mat, tripod, bunsen burner, acid, insoluble solid, stirring rod, paper filter, funnel, beaker, evaporating basin and petri dish
Preparation: Gently warm an acid using a bunsen burner
add insoluble solid (stirring) until it no longer reacts
Filtration: Filter the solution to remove the excess insoluble solid
(This will leave a solution of salt dissolved in water)
Crystallization: Heat the solution in an evaporating basin
After heated pour the solution into a petri dish
Leave the solution to cool and allow more water to evaporate
The salt will begin to crystallize and form
If two solutions of soluble salts are mixed together what are the two salts it produces
a soluble and an insoluble salt.
What does the insoluble salt produce in a reaction between two soluble salts
A precipitate - a solid made in the solution
This process is called precipitation
What is an example of the process of precipitation
Na2CO3 (aq) + CuSO4 (aq) ==> CuSO3 (s) + Na2SO4 (aq)
insoluble salt is shown as an (s)
if a substance is aqueous it is
soluble in water
Steps and apparatus for the practical of making a precipitate of an insoluble salt
Apparatus: measuring cylinder, 2 test tubes, filter paper, stirring rod, funnel and beaker
Steps: Add exact amounts of the 2 salt solutions together
After that an insoluble salt will form as a precipitate which is solid
Pour the test tube into a funnel where the insoluble salt will be collected as residue at the top.
Take out the lamp filter paper with the insoluble salt in it.
Wash the residue with a little cold water and leave it out to dry.
What is the experiment method which involves an acid and an alkali
titration experiement
What does a titration determine
the volumes of acid and alkali that must be mixed to obtain a solution of only salt and water
Steps and apparatus for carrying out a titration between an acid and alkali
Apparatus: Pipette, burette, conical flask, safety pipette filter, white tile and clamp stand
Steps: Use the pipette and pipette filler to add a measured volume of sodium hydroxide solution to a clean conical flask.
Add a few drops of indicator and put the conical flask on a white tile.
Fill the burette with hydrochloric acid and note the starting volume.
Slowly add the acid from the burette to the alkali in the conical flask, swirling to mix.
Stop adding the acid when the end-point is reached (when the indicator first permanently changes colour). Note the final volume reading.
Repeat the steps again with a new batch to get more accurate results.
Ions of metals are
cations
Steps of flame test and what it produces
Steps: Dip a piece of nichrome wire into concentrated HCI solution,
Dip it into a solid compound
Put it over a blue bunsen flame
The color seen in the flame identifies the metal ion in the compound
Lithium = bright red Sodium = Golden yellow/orange Potassium = lilac Copper = green
