Acids and Bases Overview

Acids and Bases

• Acids are chemicals that produce acidic substances with a pH less than 7.
• Bases are chemicals that produce basic substances with a pH greater than 7.

Properties of Acids and Bases

• Acids:

  • Taste: Sour
  • Feel: Stinging
  • Acidic

• Bases:

  • Taste: Bitter
  • Feel: Slippery
  • Basic

• Tasting and feeling unknown chemicals is unacceptable for identification.

Indicators

• Indicators are substances that change colour when reacting with acids and bases.
• Bromothymol Blue and Universal Indicator are examples.
• Universal Indicator has a range of colours based on pH.

Litmus

• Litmus is a chemical indicator, a mixture of plant compounds extracted from lichens.
• Litmus is light pink before reactions.
• In the presence of acid, litmus turns red.
• In the presence of base, litmus turns blue.
• Litmus provides an approximate measure of acidity or basicity.

Neutralization

• Acids and bases react together when mixed, forming a neutralisation reaction.
• Both acid and base are used up in the reaction.
• A salt and water are produced.

pH Scale

• The pH scale is a more specific way to compare acids and bases.
• The scale ranges from 0 to 14.
• A pH of 7 is neutral.
• Lower than 7 is acidic.
• Higher than 7 is basic.
• Each pH unit represents a 10-fold increase.
• Universal indicator or pH paper changes colour based on the pH
• Colours can be matched to a chart to determine the known pH value

Acid Rain

• Rainwater is naturally slightly acidic.
• When rainwater combines with atmospheric chemicals (like sulfur dioxide or nitrogen dioxide), it results in acid rain, which can have a pH as low as 3 in some places.
• This can have damaging effects on living organisms.
• Normal rain/snow has a pH of 5.6.
• Anything lower than 5.6 is considered acid rain/snow.
• Acid rain can lower the pH of water in lakes, further damaging the surrounding environment.
• Acids that contribute to acid rain include sulfuric acid, sulfurous acid, nitrous acid, nitric acid and carbonic acid.

Neutralizing Acidic Lakes

• Acidic lakes can be treated with lime (calcium hydroxide) to neutralize them.
• The lime is mixed with water and dissolves, forming a base.
• The chemical reaction between the limewater and the lake's dilute sulfuric acid produces calcium sulfate and water.

Using Chemistry to Control Acid Effects

• Scrubbers: Limestone mixed with water absorbs sulfur particles in toxic gases, preventing them from entering the atmosphere.
• Catalytic converters: Ceramic or wire honeycomb coated with metals (like platinum) act as catalysts for complete combustion. This reduces the formation of carbon monoxide and nitrogen oxides.

Acid Rain Impact Visual representation

• Visual depictions of the impact of acid rain on the environment.