U1-3 - Acids and Bases Flashcards
What is pH?
A number that measures how acidic or alkaline something is.
(Usually 0–14)
Acidic solutions have pH…
less than 7.
Alkaline solutions have pH…
more than 7.
Neutral solutions have pH…
equal to 7.
Colour of universal indicator in neutral solutions
Green
Colour of universal indicator in alkalis
Blue/purple
Colour of universal indicator in acid
Red
(red/orange/yellow)
Ions which make a solution acidic
H+ (hydrogen)
Ions which make a solution alkaline
OH– (hydroxide)
Formula for hydrochloric acid
HCl
Formula for sulfuric acid
H2SO4
Formula for nitric acid
HNO3
Acid
Substance which contains hydrogen ions (H+)
Alkali
Substance which contains hydroxide ions (OH–)
Why is water neutral?
Equal numbers of H+ and OH– ions.
Formula for phosphoric acid
H3PO4
If an alkali is diluted, the pH …
decreases.
If an acid is diluted, the pH …
increases.
If a solution is diluted, the concentrations of H+ and OH– ions …
decrease.
If a solution is diluted, the pH moves towards…
7.
(it cannot go past 7)
Soluble metal oxides turn solution pH…
alkaline.
Soluble non-metal oxides turn solution pH…
acidic.
Insolube oxides turn solution pH…
neutral (no effect).
Environmental problems caused by non-metal oxide gases
Acid rain, ocean acidification, greenhouse effect.
Gases which cause acid rain
Carbon dioxide, sulfur dioxide, nitrogen oxides
Neutralisation
A reaction between an acid and a base which produces a salt and water.
Base
A substance which can neutralise an acid
Salt
A compound made when the hydrogen ions in an acid are replaced by metal ions.
Metal …., ….and … are bases.
Metal oxides, hydroxides and carbonates are bases.
Metal hydroxide + Acid → …
Salt + Water
A compound made when the hydrogen ions in an acid are replaced by metal ions.
Salt
Sulfuric acid makes …. salts.
sulfate
Hydrochloric acid makes …. salts.
chloride
What is the difference between a base and an alkali?
Both neutralise acids, but an alkali must also be soluble in water
Metal oxide + Acid → …
Salt + Water
Metal carbonate + Acid → …
Salt + Water + Carbon dioxide
Soluble base
Alkali
Sodium chloride is a salt.
Where does the ‘sodium’ part come from?
Parent base
(sodium oxide, hydroxide or carbonate)
Sodium chloride is a salt.
Where does the ‘chloride’ part come from?
Parent acid
(hydrochloric acid)
Phosphoric acid makes …. salts.
phosphate
Nitric acid makes …. salts.
nitrate
Colour of phenolphthalein in alkaline solutions
Pink
An insoluble metal carbonate reacts with an acid.
How do you know the reaction is finished?
Effervescence (fizzing) has stopped.
Lab technique used to separate a solid from a liquid.
Filtration
Lab technique used to separate a dissolved solid from a liquid.
Evaporation
Why are acids added to food?
To improve flavour or to act as preservatives
Preservative
A substance which prevents food from spoiling
(e.g. ascorbic acid)
Negative effects of consuming too much acidic food/drink
Tooth decay, indigestion
Colour of phenolphthalein in acidic and neutral solutions
Colourless
(NOT clear!)
What is the point of titration?
To find out an unknown concentration.
During a titration, what tells you the reaction is finished?
The first permanent colour change
