Sodium Potassium Tartrate (Rochelle Salt)

What is Sodium Potassium Tartrate?

Sodium potassium tartrate is a double salt of tartaric acid with a chemical formula C₄H₄O₆KNa·4H₂O. It is also known as Rochelle salt or Potassium sodium tartrate.

It is a colourless to white crystalline powder with a cool and saline taste. It has a pH value of 6.5 – 8.5. It has a large piezometric effect which makes it widely useful in sensitive vibrational and acoustic devices.

Table of Contents

• • Preparation of Sodium Potassium Tartrate
  • Properties of Sodium Potassium Tartrate
  • Structure of Sodium Potassium Tartrate
  • Uses of Sodium Potassium Tartrate
  • Assay
  • Frequently Asked Questions – FAQs

Preparation of Sodium Potassium Tartrate

The detailed procedure for the preparation of sodium potassium tartrate is given below.

Apparatus and ingredients required:

1. 500 g of sodium bicarbonate
2. 200 g of potassium bitartrate
3. Pyrex container
4. 500 ml of a pyrex measuring cup
5. Measuring spoon of 2 ml
6. Coffee filter
7. Jar with lid
8. Oven
9. Spoon to stir
10. Filter paper
11. Water
12. Saucepan

Step-1:

To convert sodium bicarbonate to sodium carbonate follow the steps given below:

• Take a pyrex container and add 500 g of sodium bicarbonate (baking soda).
• Place it in the oven for an hour at 65 °C.
• Set the temperature to 120 °C and keep it for another one hour.
• Repeat the previous step for 175 °C and 230 °C.
• Take out the container from the oven and let it cool to room temperature.
• Transfer the washing soda (sodium carbonate) into a sealed container.

Step-2:

Potassium bitartrate (cream of tartar) reacts with sodium carbonate to generate sodium potassium tartrate (Rochelle salt):

• Take a beaker of capacity 500 mL. Add 250 mL of water in it. Suspend 200 g of potassium bitartrate in the beaker containing water.
• Take a saucepan with water, place the beaker, and heat it.
• Heat till you observe the outer water simmering.
• Add 2.5 mL of the washing soda obtained from part 1 experiment into the beaker. Stir it well and the solution will bubble.
• Continue adding sodium carbonate until no more bubbles are observed in the solution.
• Once there are no bubbles formed in the solution, filter it with the help of filter paper.
• You can also use a coffee filter to filter the hot solution.
• Evaporate to concentrate the solution to 400 mL by heating.
• Let the filtrate cool and store it in a cool place.
• After several days of storing, with the process of decantation, collect the resulting crystals.
• Use filter paper to dry the crystals.

NOTE: About 210 g of sodium potassium tartrate (Rochelle salt) is obtained.

Chemical Reaction Involved in the Preparation of Rochelle Salt

Conversion of sodium bicarbonate to sodium carbonate

2NaHCO₃ → Na₂CO₃ + CO₂ + H₂O

Potassium bitartrate (cream of tartar) reacts with sodium carbonate to generate sodium potassium tartrate (Rochelle salt):

KHC₄H5O₆ + Na₂CO₃→ C₄H₄O₆KNa·4H₂O

Properties of Sodium Potassium Tartrate 

Structure of Sodium Potassium Tartrate

Sodium Potassium Tartrate – Structure of Rochelle salt

The above image describes the structure of Sodium potassium tartrate. C₄H₄O₆KNa·4H₂O is the chemical formula of Sodium potassium tartrate which has ten oxygen atoms, twelve hydrogen atoms, four carbon atoms, one potassium atom, and one sodium atom.

Uses of Sodium Potassium Tartrate (C₄H₄O₆KNa·4H₂O)

• Sodium potassium tartrate is used as a laxative.
• It is used in the silvering of mirrors.
• It is one of the ingredients in Fehling’s solution.
• It is used in the electroplating process.
• It is used in cigarette paper.
• It is used to break up emulsions.
• It is one of the ingredients in Biuret reagent to measure the concentration of protein.
• It helps to maintain alkaline pH.
• It is used as a common precipitant in protein crystallography.

Assay

An accurately weighed quantity of the substance is carbonized in the porcelain dish. The residue is extracted with water and sulphuric acid. The solution is filtered and the residue is washed with more water. The filtrate and washings are combined and titrated for the excess acid with sodium hydroxide using methyl orange as an indicator.

Learn more about the chemical properties and importance of Rochelle salt (sodium potassium tartrate) (C₄H₄O₆KNa·4H₂O) from the expert faculties at BYJU’S.

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