# How do you calculate the Ka for the weak acid with pKa of 0.21.?

${K}_{a}$ $=$ ${10}^{- 0.21}$ $=$ ??
The $p$ function means to take the negative of the log to the base 10. The same for $p H$; here, if $p H$ $=$ $1$, then $\left[{H}^{+}\right]$ $=$ ${10}^{-} 1$ $m o l \cdot {L}^{-} 1$. I recommend that you have a good look at your texts, and get this concept straight.
For instance when we write ${\log}_{a} b = c$, we are saying that ${a}^{c}$ $=$ $b$. For practice, can you tell me what ${\log}_{10} 100$, and ${\log}_{10} 1000$ are? Years ago, (20-30 years), before the advent of cheap electronic calculators, students used to be issued with log tables for multiplication and division.