Potassium dichromate is less soluble than sodium dichromate as sodium ions have higher hydration than potassium ions due to the smaller size of sodium ions.
Potassium dichromate is widely used in redox titration as primary standard.
The six terminal Cr-O bond lengths are equal due to resonance and have different bond lengths than compared the two bridge Cr−O bond lengths as these bridge Cr−O bonds are not involved in resonance.
Potassium dichromate is used as a primary standard as it is available in high purity and its solutions have long-lasting stability in acid and are stable to light, to most organic matter and other environmental factors.
