1.7 Acids and Bases Flashcards
What does pH stand for?
potential Hydrogen.
What is the pH scale?
The pH scale gives us an indication of how acidic or alkaline a substance is. Using the pH scale, we measure the concentration of hydrogen ions.
pH number meaning.
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• A pH of BELOW 7 indicates an acidic solution. (The pH paper or
universal indicator solution turns a red or orange colour.)
• A pH of ABOVE 7 indicates an alkaline solution. (The pH paper or
universal indicator solution turns a blue or purple colour.)
• A pH of 7 is a neutral solution such as pure water. (The pH paper or
universal indicator solution will turn green.)
What do acidic solutions contain?
Acidic solutions have a pH of between 1 and 6. This is because they contain H+ ions in a greater concentration than OH- ions.
H+ ions are why acids react like they do and all acidic solutions contain
H+ . All acids contain ions and as a result they conduct electricity, becausethe ions are free to carry the charge.
When an acid is diluted with water the concentration of H* ions is
decreased. This increases the pH of the solution toward 7 because the
acid is becoming less acidic.
What are the common acids?
Hydrochloric Acid : HCl : H+ (aq)Cl-(aq)
Sulphuric Acid: H2SO4: (H+)2 (aq) (SO4)2- (aq)
Nitric Acid: HNO3 : H+ (aq) (NO3)- (aq)
Ethanoic Acid: CH3COOH : H+(aq) CH3COO- (aq)
What do alkaline solutions contain?
Alkaline solutions have a pH of between 8 and 14. This is because they
contain OH ions. The presence of OH ions is the reason why alkalis
react like they do and all alkaline solutions contain OH. Like acids, alkalis
conduct electricity because they have ions that are free to carry the
charge.
When an alkali is diluted with water the concentration of OH ions is
decreased. This decreases the pH of the solution toward 7 because the
alkali is becoming less alkaline.
What are the common alkalis?
Sodium hydroxide: NaOH : Na+(aq) OH-(aq)
Calcium hydroxide: Ca(OH)2: Ca2+(aq) (OH-)2 (aq)
Lithium hydroxide: LiOH: Li+(aq) OH-(aq)
How do you make acids and alkalis?
Acids and alkalis can be formed by dissolving different oxides in water.
When a non-metal oxide is dissolved in water an acidic solution is
produced. If a soluble metal oxide, known as a base, is dissolved in water,
an alkaline solution is produced.
Metal oxides such as Li2O, Na2O and K2O dissolve in water to produce
alkaline solutions (solutions with a pH greater than 7). Notice that all the oxides of group 1 (and some of group 2) are soluble; most other metal
oxides are insoluble.
Key Point !
- Soluble non-metal oxides produce acids.
- Soluble metal oxides (bases) produce alkalis.
What is a neutral solution?
Neutral solutions such as water have equal concentrations of OH- and H+
ions which cancel each other out. It is because of this small amount of
ions that water can conduct electricity.
What is neutralisation?
Neutralisation is the reaction of an acid with a base such as an alkali,
metal oxide, metal hydroxide or carbonate. This moves the pH of the acid
upwards toward 7 and the pH of the alkali downwards toward 7. All
neutralisation reactions produce water.
The main two equations of neutralisation:
acid + alkali —> salt + water
acid + base —> salt + water
After neutralisation, how do you name the salt produced?
The name of the salt produced is dependent on the acid and alkali that
reacted.
Eg:
Hydrochloric Acid + Sodium hydroxide —> sodium chloride + water
Hydrochloric Acid : Chloride
Sulphuric Acid: Sulphate
Nitric Acid: Nitrate
What is a spectator ion?
A spectator ion is like a spectator at a football match. They are there at
the game but are not taking part in the game. They are simply spectators
watching the reaction taking place.
The spectator ions are ions that are present during the reaction, but are
unchanged by the reaction.
What are titrations?
An acid- base titration is a procedure which is used to determine the
concentration of an acid. An accurately measured volume of a base of
known concentration is reacted with an acid until the acid is neutralised.
An indicator is usually added to provide a colout change at the point
when neutralisation is complete.
What concentration is a sulphuric acid solution if 500cm3 is neutralised by 500cm3 of 4 mol l-1 sodium hydroxide?
P = 2 (H2SO4) V = 500cm3 = 0.5L C= ???
P = 1 (NaOH) V = 500cm3 = 0.5L C = 4 mol l-1
PVC (acid) = PVC (alkali)
2 x 0.5 x C = 1 x 0.5 x 4
1 x C = 2
C= 2
—
1
C= 2 mol l-1
