Why would NAOH solution need to be added when preparing the K2CrO4 stock solution?
the chromate ion is unstable, and in slightly acid solutions, it changes to the dichromate ion. So adding the sodium hydroxide keeps the pH basics, and keeps the chromate ion a chromate ion.
Thanks to bobpursley for answering my question.
To understand why NaOH solution needs to be added when preparing the K2CrO4 stock solution, we need to understand the concept of solubility.
K2CrO4 is potassium chromate, a salt that is commonly used in laboratories. It is generally prepared as a stock solution to be used in various chemical reactions or analytical tests. However, K2CrO4 has limited solubility in water, meaning that it does not dissolve easily.
By adding NaOH solution (sodium hydroxide) during the preparation of the K2CrO4 stock solution, the pH of the solution is increased. This increase in pH helps to shift the equilibrium between the dissolved and undissolved forms of K2CrO4, thereby improving its solubility.
Specifically, when NaOH is added, it reacts with the chromate ions (CrO4^2-) to form a more soluble compound known as sodium chromate (Na2CrO4). This reaction is:
2 NaOH + H2CrO4 -> Na2CrO4 + 2 H2O
Since sodium chromate (Na2CrO4) has better solubility in water compared to potassium chromate (K2CrO4), adding NaOH helps to increase the amount of dissolved K2CrO4 in the stock solution. As a result, the K2CrO4 solution becomes more concentrated, making it more suitable for various applications such as titrations or qualitative analysis.
In summary, NaOH is added to the K2CrO4 stock solution to increase its solubility by shifting the equilibrium between the dissolved and undissolved forms of K2CrO4. This results in a more concentrated and usable stock solution for laboratory purposes.