1003170802

The acidity of a substance is measured by its $pH$ value. In practice, $pH$ is often assumed to be the negative logarithm of the hydrogen ion concentration $H^{+}$ (i.e. the number of moles of hydrogen ions per liter of solution): $$pH=-\log (H^{+}).$$ If an apple juice has a $pH$ of $3.8$ and a grapefruit juice has a $pH$ of $3.6$ then the hydrogen ion concentration ($\mathrm{mol}/\mathrm{l}$) in the apple juice is how much less than in the grapefruit juice? Round the result to six decimal places.