Properties of Acids

Properties of Acids

• Acids are liquids.
• Concentrated acids can be corrosive.
• Acids taste sour.
• Acids turn blue litmus paper red.
• Acids react with metals to form salts.
• Acids contain hydrogen ions.
• Acids turn Universal Indicator from green to red and have a pH less than 7.
• Examples of acids include vinegar (ethanoic acid) and lemon juice (citric acid).
• Common acids used in school laboratories include hydrochloric acid (HCl), nitric acid (HNO3), and sulphuric acid (H2SO4).

Properties of Alkalis

• Alkalis feel soapy to touch.
• Like acids, alkalis can burn the skin.
• Alkalis turn red litmus paper blue.
• Alkalis contain hydroxide ions (OH-).
• Alkalis taste bitter.
• Alkalis turn Universal Indicator from green to blue or purple.
• Common alkalis used in school laboratories include sodium hydroxide (NaOH), ammonia (NH3/NH4OH), and calcium hydroxide (Ca(OH)2).

Properties of Neutral Substances

• Litmus paper is not affected by neutral substances.
• Neutral substances tend to be harmless.
• Universal Indicator stays green in neutral substances.
• Examples of neutral substances include water, sodium chloride solution (NaCl), and sugar solution (C6H12O6).

Identifying Acidic or Alkaline Solutions

Litmus Paper Test

• Acidic solutions turn blue litmus paper red and keep red litmus paper red.
• Neutral solutions keep red litmus paper red and blue litmus paper blue.
• Alkaline solutions turn red litmus paper blue and keep blue litmus paper blue.

pH Scale and Indicators

• The strength of an acid or alkali is shown using a scale of numbers called the pH scale.
• The pH scale ranges from 0-14.
• Acidic solutions have a pH less than 7.
• Neutral solutions have a pH of 7.
• Alkaline solutions have a pH greater than 7.
• Universal indicator changes color depending on the pH of the solution.
• Universal indicator can be used to prepare homemade indicators from red cabbage or beetroot juice.