chemistry - acids and alkali
DESCRIPTION
Basics of Chemistry on Acids and AlkalisTRANSCRIPT
Acids and Alkalis
Physical and Chemical Properties
Properties of Acids
1. Acids have sour taste.
2. Acids are corrosive.
3. Acids dissolve in water to form
solutions which conduct electricity.
Acids in Foodo Citric acid (in lemons)o Ethanoic acid (in vinegar)o Carbonic acid (in soft drinks)o Tartaric acid (in grapes)o Malic acid (in apples)o Lactic acid (in yoghurt)
Weak organic acids found in food
An acid is a substance which produces hydrogen ions when it is dissolved in
water.
The hydrogen ions give an acid its acidic properties.
Acids only behave as acids when they are dissolved in water.
What is an Acid?
TAKE NOTE
NOT all substances that contain hydrogen are acids.
For example, •NH3 (ammonia) contains hydrogen but it is not an acid. •H2 (hydrogen) is also not an acid.
Properties of Alkalis
1. Alkalis have bitter taste.
2. Alkalis have soapy feel.
3. Alkalis dissolve in water to form
solutions which conduct electricity.
• An alkali is a substance which produces hydroxide ions when it is dissolved in water.
• The hydroxide ions, OH-(aq) give an alkali its alkaline properties.
• Alkalis only behave as alkalis when they are dissolved in water.
What is an Alkali?
An acid is a substance which produces hydrogen ions when it is dissolved in water.
SummaryWhat is an acid?
Hydrochloric acid, sulfuric acid, nitric acid, ethanoic acid, citric acid …
Examples of acids?
An alkali is a substance which produces hydroxide ions when it is dissolved in water.
SummaryWhat is an alkali?
Sodium hydroxide, potassium hydroxide, calcium hydroxide, aqueous ammonia
Examples of alkalis?
Indicatorso An indicator is a substance which changes
colour depending on whether the solution tested is acidic or alkaline.
o There are many types of indicators, including the universal indicator and litmus indicator.
Litmus Indicator• Acids turn blue litmus paper red.o Litmus paper exists in two colours, red and
blue. • Alkalis turn red litmus paper blue.
Acids + Metals
Acids react with some metals to form a salt and hydrogen gas.
hydrochloric acid magnesiu
m
magnesium chloride
hydrogen gas+ +
sulfuric acid magnesium
magnesium sulfate
hydrogen gas+ +
1
Acid + Metal Salt + Hydrogen gas
Acids + Metals
The type and name of salt depends on the acid used.
Reaction with
• Hydrochloric acid
• Sulfuric acid
• Nitric acid
Chloride salts
Sulfate salts
Nitrate salts
Acids + Metals
Acids react with some metals to form a salt and hydrogen gas.
Some metals which can react with acids are magnesium, aluminium, zinc and iron.
Explosive reactions occur when using reactive metals like lithium, sodium and potassium.
Exception:
Unreactive metals such as copper and silver do not react with dilute acids.
Acids + Metals
How to test for hydrogen gas? Place a lighted splint in the presence of the gas.
If hydrogen is present, the lighted splint will be extinguished with a ‘pop’ sound.
Acids + Carbonates
Acids react with carbonates to form a salt, carbon dioxide gas and water.
2
hydrochloric acid
sodium carbonate
sodium chloride
carbon dioxide
gas+ +
nitric acid calcium carbonate
calcium nitrate
+
water+
carbon dioxide
gas+ water+
Acid + Carbonate Salt + Carbon dioxide gas + Water
Acids + Carbonates
How to test for carbon dioxide gas? Bubble the gas through limewater.
Carbon dioxide forms a white precipitate with limewater.
Acids + Carbonates
How to test for carbon dioxide gas? Bubble the gas through limewater.
Carbon dioxide forms a white precipitate with limewater.
Limewater
Bubble carbon
dioxide gasWhite
precipitate formed
Acids + Alkalis
Acids react with alkalis to form a salt and water only.
The reaction between acids and alkalis is called
neutralisation.
3
Acid + Alkali Salt + Water
Acids + Alkalis
Examples:
hydrochloric acid
sodium hydroxide
sodium chloride
Water+ +
sulfuric acidpotassium hydroxide
potassium sulfate
Water+ +