Chapter 5 - Acids, bases and salts Flashcards
What is an indicator ?
An indicator is one colour in acid and a different colour in alkali
What colour is blue and red litmus paper in acids and alkalis
in acid in alkali in neutral
RED red blue red
BLUE red blue blue
What colour does Phenolphthalein go in acid alkali and neutral solutions ?
acid : colourless
alkali : pink
neutral : colourless
What colour does Methyl orange go in acid alkali and neutral solutions ?
acid : red
alkali : yellow
neutral : orange
What is an acid ?
An acid is a substance that dissolves in water producing hydrogen ions (H+(aq))
What negative ion does all 3 acids produce ?
hydrochloric acid (HCL) : chloride sulfuric acid (H2SO4) : sulfate nitric acid (HNO3) : nitrate
What is an alkali ?
An alkali is a substance that dissolves n water producing hydroxide ions
What classifies a strong acid ?
Strong acids completely ionise in water
What classifies a weak acid ?
Weak acids are acids that are partially ionise in water
What is a strong alkali ?
Strong alkalis are alkalis that are completely ionised in water
What is a weak alkali ?
Weak alkalis are alkalis that are partially ionised in water
Explain the pH scale
- pH 7 in neutral
- pH less than 7 is acidic
- pH more than 7 is alkaline
What is the pH of a strong acid and give some examples
pH 0-2
examples : sulfuric acid, hydrochloric acid
What is the pH of a weak acid and give some examples
pH 3-6
examples : ethanoic acid, carbonic acid
What is the pH of a weak alkali and give some examples
pH 8-11
examples : ammonia
What is the pH of a strong alkali and give some examples
pH 12-14
examples : sodium hydroxide and potassium hydroxide
What is the pH of a neutral and give some examples
pH 7
examples : water
What is a more accurate way of finding the pH ?
Use a pH meter, this will give the pH to one decimal place
What is a concentrated acid ?
A concentrated acid contains a large number of acid particles dissolved per unit volume
What is a dilute acid ?
A dilute acid contains a small number of acid particles dissolved per unit volume
What does the hazard symbol corrosive look like, mean and give an example
Looks like : acid spilling over a hand and a work top
means : burns and destroys living tissues
examples : concentrated acid
What does the hazard symbol explosive look like, mean and give an example
Looks like : an explosion
means : explodes if exposed to flame, heat or knocked
examples : potassium
What does the hazard symbol flammable look like, mean and give an example
Looks like : a flame
means : catches fire easily when in contact with air
examples : ethanol
What does the hazard symbol toxic look like, mean and give an example
Looks like : skull and crossbones
means : can kill by poisoning
examples : weed killer, cyanide
What does the hazard symbol moderate hazard look like, mean and give an example
Looks like : an exclamation mark
means : may be harmful or an irritant
examples : dilute sodium hydroxide
What is a salt ?
A salt is the compound formed when some or all of the hydrogen ions of an acid are replaced by metal or ammonium ions
What are some general observations that can be made during an acid reaction ?
- bubbles
- solid disappears and solution is produced
- heat released
What is the general equation when a metal reacts with an acid ?
metal + acid —- > salt + hydrogen
What is the test for hydrogen ?
- apply a lighted splint
- a popping sound results
What is the general equation for an acid plus a base ?
base + acid —-> salt + water
What is a base ?
A base is a metal oxide or metal hydroxide that neutralises an acid to produce a salt and a water
What is an alkali ?
a soluble base
What does the term neutralisation mean ?
Neuralisation is the reaction between the hydrogen ions in an acid and the hydroxide ions in an alkali to produce water
What is the ionic equation for neutralisation ?
H+ (aq) + OH- (aq) ——> H20 (l)
What is an exothermic reaction ?
An exothermic reaction is one which heat energy is given out.
What is the general equation for a metal carbonate and an acid ?
Metal carbonate + acid —-> salt + water + carbon dioxide
What is the test for carbon dioxide ?
- bubble the gas into colourless limewater
- the solution will turn milky if CO2 is present
What is the equation for ammonia and an acid ?
ammonia + acid —-> ammonium salt
What is the method of preparing metal, oxide and carbonate salts ?
add excess insoluble substance to the acid
What is the method of preparing a hydroxide salts ?
add acid to alkali in the presence of an indicator
How would you dry crystals ?
- between sheets of filter paper
- in a low-temperature oven
- in a desiccator
