The $\text{pH}$ scale for acidity is defined by $\text{pH} = -\log_{10}[\text{H}^+]$ where $[\text{H}^+]$is the concentration of hydrogen ions measured in moles per liter (M). A substance has a hydrogen ion concentration of $[\text{H}^+]= 3.4 \times 10 ^ {- 7 }$M. Calculate the $\text{pH}$ of the substance.