Acids and Alkalis

• Indicator


  A substance that changes colour in the presence of acids and alkalis
• Litmus


  Red in acid, blue in alkali
• Acid

  something when dissolved in water dissociates (breaks apart) to give a hydrogen ion
• Alkali

  something when dissolved in water dissociates (breaks apart) to give a hydroxide ion
• Universal indicator is made from a mixture of different indicators. it gives a range of colours depending on the strength of the acid or alkali
• red cabbage is a single indicator
• single indicators give a different colour for acids and alkalis but can’t tell us how strong the acid or alkali is
• When you mix an alkali and an acid you get a neutral substance
• neutral substance:

  to get the same amount of hydrogen and hydroxide ions
• when we add an alkali to neutralise acid the colour changes form red to green to blue on the ph scale
• Hydrochloric acid + sodium hydroxide -> sodium chloride + water
• sodium hydroxide + calcium carbonate-> calcium oxide + water
• sodium hydroxide + sulfuric acid-> sodium sulfate+water
• magnesium hydroxide + hydrochloric acid -> magnesium chloride +water
• (metal hydroxide + acid ->

  metal-acid + water)