An aldehyde RCHO is dissolved in water to a total concentration (free aldehyde plus hydrate) of 0.20 M. At equilibrium $K = [hydrate] / [RCHO] = 2.3$ (the concentration of water is included in $K$ ). Calculate the equilibrium concentration of free RCHO in $mmol L^{- 1}$ , to the nearest integer.

Numerical answer type, tolerance 0.5.

Answer: 61

Let free aldehyde

= x

; then hydrate

= 2.3 x

and

x + 2.3 x = 0.20

M. So

x = 0.20/3.3 = 0.0606

M, i.e.

60.6 mmol L^{- 1}

, which is 61 to the nearest integer.