acids and alkalis
Give examples of weak alkalis and their uses
1 Sodium bicarbonate in indigestion tablets or magnesium hydroxide (milk of magnesia) can used to neutralise excess stomach acid in indigestion 2. Magnesium hydroxide in Toothpaste used to neutralise teeth acid formed by bacteria feeding on food left on the teeth 3. Ammonia in fertilisers to make nitrate salts which can then provide nitrogen for plant growth
What are the hazards of alkalis?
1. Corrosive - more than acids (hence used as drain cleaners e.g. sodium hydroxide =caustic soda) 2. Irritant
What are the uses of neutralisation?
1. Indigestion tablets eg magnesium hydroxide 2. Toothpaste eg magnesium hydroxide 3. Fertilisers eg ammonia 4. Liming -Neutralisation of soil by adding lime (calcium hydroxide) to improve crop yield 5. Bee sting (acid ) use bicarbonate of soda wasp sting (alkaline) use vinegar
What are the types of indicators?
1. Universal indicator 2. Litmus 3. Red cabbage
How can you test for an acid or alkali?
1. Use an indicator 2. Use a ph meter
Give 2 examples of a strong alkali and their uses
1. sodium hydroxide (NaOH) - caustic soda- used to clean drains and make soaps 2. Calcium hydroxide (limewater) -used to make soils less acid so crop yield can increase
What is an acid?
An acid is a substance containing hydrogen atoms with a ph <7
What is an alkali?
An alkali is a substance with a ph>7 An alkali is a soluble base and forms hydroxide ions when dissolved in water. eg sodium hydroxide (so all alkalis are bases) A base is a substance ( metal oxide, hydroxide or carbonate) that reacts with an acid to form a salt plus water. Not all bases are soluble so not all bases are alkalis
What is an indicator?
An indicator is a dye that changes colour depending on whether it is in an acid or in an alkali
What are the properties of an alkali?
Bitter taste Soapy feel Corrosive - more than acids (hence used as drain cleaners e.g. sodium hydroxide =caustic soda)
What type of weak acids are there?
Citric acid- lemon juice used as a preservative to stop fruit from decomposing and as a flavouring (sour) taste Ethanoic acid- vinegar used as a flavouring and a preservative Ascorbic acid- Vitamin C used for growth and development plus helps absorption of iron (deficiency causes scurvy, anaemia and bleeding gums with loose teeth e.g. in sailors) Lactic acid- produced by bacteria in sour milk
What does corrosive mean?
Destroys living tissue e.g. skin and eyes
What types of strong acids are there?
Hydrochloric acid (HCL) makes chloride salts e.g. in stomach Sulphuric acid (H2SO4) makes sulphate salts e.g. in car battery Nitric acid (HNO3) makes nitrate salts for fertilisers
What does litmus show?
Litmus- detects only whether a substance is an acid or alkali and now how acid or alkaline it is . Acid turns blue litmus red ALkali turns red litmus bLue
What happens when an acid is added to a metal?
MASH if the metal is above hydrogen in the reactivity series and More reactive metals react more violently Copper, gold and silver do not react as they are below hydrogen in the reactivity series
Can an acid be made weaker by adding water?
NO - it will just be a more dilute concentration ALSO always ADD ACID to water and not water to acid as it will heat up and spit acid at you
What is neutralisation?
Neutralisation is the process when an acid and alkali form a salt and water
What does red cabbage show?
Red cabbage contains a pigment called anthocyanin -turns red with acid -purple is neutral so no change -turns green/yellow with alkali Tumeric is another naturally occurring indicator
What are the properties of an acid?
Sour taste eg vinegar ethanoic acid Corrosive - destroys living tisse e.g. skin and eyes Reactions: Can be neutralised by an alkali or base Can react with some metals to produce hydrogen Can react with carbonates to produce carbon dioxide
What does universal indicator show?
Universal indicator gives different colours on a logarithmic ph scale of 1-14 . Acid is red (strong) or yellow (weak) Neutral is green ph 7 e.g. milk and water Alkaline is blue (weak) and purple (strong) Says how acid or alkaline the substance is
