C2.6 Acids, bases and salts
- Created by: Elise-741
- Created on: 01-05-17 15:59
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- Acids, bases and salts
- An Indicator is just a dye that changes colour e.g. Universal Indicator
- An acid is a substance with a pH of less than 7.
- Acids form H+ ions in water
- A base is a substance with a pH of greater than 7
- An alkali is a base that dissolves in water.
- Alkalis form OH- ions in water
- General Formulas
- Neutralisation: acid + base = salt + water
- Acid + metal = salt + hydrogen
- Acid + metal oxide = salt + water
- Acid + metal hydroxide = salt + water
- Soluble or Insoluble?
- Most chlorides, sulfates and nitrates are soluble in water (exclusions are lead chloride and sulfate and silver chloride)
- Most oxides and hydroxides are insoluble in water
- Making Salts
- Soluble Salts: using a metal or insoluble base (metal oxide or hydroxide)
- E.g. to make Copper Chloride mix Hydrochloric Acid and Copper Oxide
- You add the metal and the metal oxide/hydroxide to the acid
- Solid will dissolve in acid as it reacts and the acid has been neutralised when excess solid sinks to the bottom
- Filter out excess metal, metal oxide/hydroxide to get a salt solution
- For pure, solid crystals of salt leave the water to evaporate (crystallisation)
- Filter out excess metal, metal oxide/hydroxide to get a salt solution
- Solid will dissolve in acid as it reacts and the acid has been neutralised when excess solid sinks to the bottom
- You add the metal and the metal oxide/hydroxide to the acid
- E.g. to make Copper Chloride mix Hydrochloric Acid and Copper Oxide
- Soluble Salts: using an alkali
- Add exactly the right amount of alkali to the acid to neutralise - you'll need to use an indicator
- Repeat using the same volumes without the indicator so the salt isn't contaminated
- Evaporate off the water to crystallise
- Repeat using the same volumes without the indicator so the salt isn't contaminated
- Add exactly the right amount of alkali to the acid to neutralise - you'll need to use an indicator
- Insoluble Salts: using precipitation reactions
- Pick two solutions that contain the required ions
- E.g. to make Lead Chloride you need a lead solution and a chloride solution so Lead Nitrate solution (most nitrates are soluble) with Sodium Chloride solution (all group 1 compounds are soluble)
- Leave the salt to precipitate out, filter it from the solution, wash and dry it on filter paper
- E.g. to make Lead Chloride you need a lead solution and a chloride solution so Lead Nitrate solution (most nitrates are soluble) with Sodium Chloride solution (all group 1 compounds are soluble)
- Pick two solutions that contain the required ions
- Soluble Salts: using a metal or insoluble base (metal oxide or hydroxide)
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