Added labs expand knowledge of chemical reactions. Homework and free class moments are infused with review on the above mentioned topics before pushing on to stoichiometry. Second, the math is somewhat foreign to the student. Chemistry is the first exposure to the factor label method for most students. This is for ease of checking their setups through cancellation of labels.
Many students lose focus on each step.
They question the reasoning behind each of these steps as they should. Unfortunately, this questioning can last more than a month. It takes this long for an algorithm to be firmly established. They have difficulty synthesizing many small steps into one large one. Stoichiometry involves a grand synthesis with many higher order thininkg skills.