Acids, alkalis and salts

• Indicators are used to determine whether a solution is acidic or alkaline.
• Acids react with metals, bases and carbonates to produce salts.
• Neutralisation is the reaction between an acid and a base.
• Acids produce hydrogen ions, H + , in aqueous solution.
• Alkalis produce hydroxide ions, OH - , in aqueous solution.
• Acids have a pH lower than 7, making them acidic.
• Alkalis have a pH greater than 7, making them alkaline.
• Alkaline solutions have pH values greater than 7.
• A neutral solution has a pH value of 7.
• The pH scale measures the acidity or alkalinity of a solution.
• The pH of a solution can be measured using a pH probe, or estimated using universal indicator.
• Universal indicator is a chemical solution that produces many different colour changes corresponding to different pH levels.
• Indicators show whether a solution is acidic, neutral (pH 7) or alkaline.
• The table shows the colours for litmus paper.
• Red litmus turns blue in alkalis, while blue litmus turns red in acids.
• A pH (power of hydrogen) value below 7 is acidic, a pH value above 7 is alkaline.