Chemistry - Is LiOH a weaker base than NaOH?

Solution 1:

In Proton Affinities of the Alkali Hydroxides J. Am. Chem. Soc., 1969, 91, pp 2810–2811, it is shown that gas phase affinities in $\pu{kcal/mol}$ are:

• $\ce{LiOH}$: 240.7
• $\ce{NaOH}$: 247.6
• $\ce{KOH}$: 262.6
• $\ce{CsOH}$: 269.2

So, yes, $\ce{LiOH}$ is weaker, at least in the gas phase.

In aqueous solution, ACIDITY FUNCTIONS FOR STRONGLY BASIC SOLUTIONS Chemical Reviews volume 66, pages 119-131:

the order of basicity for the same molarity of aqueous solution, $\ce{LiOH < NaOH < KOH}$.

For example, for a $\pu{1M}$ solution, the acidity function (H) is:

• $\ce{LiOH}$: 13.48
• $\ce{NaOH}$: 14.01, 14.16 (two different measurement techniques)
• $\ce{KOH}$: 14.17

So in both the gas and aqueous phases, $\ce{LiOH}$ is a weaker base than $\ce{NaOH}$.

Solution 2:

The reference

  Acids and Bases (Essential Chemistry) 
  Kristi Lew
  Publisher: Chelsea House Publications; Library Binding edition (December 1, 2008)
  Language: English
  ISBN-10: 0791097838
  ISBN-13: 978-0791097830

from page 42

I clipped the image from Goggle books. So far as I know the pKb values for LiOH, NaOH and KOH do not have a primary source listed.