Making Salts from Acids and Alkalis Notes

Making Salts - Acids and Alkalis

Objective

• Describe how to make salts by reacting acids with alkalis.

Introduction to Sodium Chloride (NaCl)

• Production: In 2010, India produced over 15 million tonnes of sodium chloride, while Egypt produced 2.4 million tonnes.
• Uses: Sodium chloride is used for:
  • Preserving and flavoring food.
  • Dyeing clothes.
  • Making other important chemicals like chlorine and sodium hydroxide.
• Extraction: On a large scale, sodium chloride is extracted from the sea or mined as rock salt.
• Lab Production: Sodium chloride can also be made in the laboratory.

Choosing Reactants for Making Salt

• Reaction of Elements (Hazardous)
  • Reacting sodium with chlorine to make sodium chloride is hazardous and produces an impure product.
  • $sodium + chlorine \rightarrow sodium chloride$
• Neutralization of Acid with Alkali (Safer)
  • Sodium chloride can be made by neutralizing an acid with an alkali.
  • $hydrochloric \ acid + sodium \ carbonate \rightarrow sodium \ chloride + water$

Azalee's Method for Making Sodium Chloride Crystals

1. Dilute Hydrochloric Acid and Universal Indicator: Start with dilute hydrochloric acid and universal indicator. The solution is red, indicating acidity.
2. Add Sodium Carbonate Solution: Add sodium carbonate solution until the solution becomes neutral (green).
3. Add Charcoal Powder: Add charcoal powder to remove the color.
4. Filter the Solution: Filter the solution to remove the charcoal powder.
5. Heat Over a Water Bath: Heat the filtered sodium chloride solution over a water bath to evaporate the water, leaving sodium chloride crystals.

Bem's Method for Making Sodium Chloride Solution

• Burette and Pipette: Bem uses a burette and pipette, along with an indicator solution, to precisely measure the volume of acid needed to neutralize 25.00 cm³ of sodium carbonate solution.
• Repeat without Indicator: After determining the correct volume, he repeats the method without the indicator to avoid contamination.
• Heating: He then heats the sodium chloride solution over a water bath to evaporate the water.

Evaluating the Two Methods

• Product Yield: Bem made more sodium chloride than Azalee, despite starting with the same amounts of reactants.
• Source of Loss (Azalee): Azalee lost some of her product because the sodium chloride solution soaked into the filter paper during filtration to remove charcoal.
• Bem's Advantage: Bem did not need to filter his mixture, avoiding the loss of product in the filtration stage.
• Evaporation Stage: Both students lost very little sodium chloride during the evaporation stage, so this was not the primary reason for the difference in yield.
• Conclusion: The difference in yield is mainly due to Azalee's filtering process.

Further Discussion on Methods

• Azalee's Perspective: Only had to do the reaction once but lost product during filtering.
• Bem's Perspective: Had to repeat the reaction (once with the indicator, once without), wasting chemicals by discarding the first mixture.
• Compromise: Azalee wasted less since she removed the indicator from her primary solution, making her method potentially better despite the filtration loss.

Review Questions

1. Separating Indicator: Describe how to separate the indicator from the salt solution when making a salt by reacting an acid and an alkali.
2. Potassium Hydroxide with Nitric Acid: Write a word equation for the reaction of potassium hydroxide with nitric acid, and name the salt made.
   • $Potassium \ Hydroxide + Nitric \ Acid \rightarrow Potassium \ Nitrate + Water$
3. Potassium Chloride Crystals: Name the acid and alkali that you could react to make potassium chloride crystals.
   • $Hydrochloric \ Acid + Potassium \ Hydroxide \rightarrow Potassium \ Chloride + Water$

Key Steps for Making Salts from Acids and Alkalis

• React an acid with an alkali using an indicator to determine the point of neutralization.
• Heat the solution to remove water, leaving the salt behind.