Using the equation of a straight line

The equation of a straight line is usually taught in the form:

y= mx + c 

which succinctly expresses the fact that if we plot y against x and the variables obey a relationship of this form we will obtain a straight line graph with gradient or slope m and intercept (where the line crosses the y -axis) c (fig 1). 

In chemistry the letter c  is often used to represent concentration so this is potentially confusing. The letter used to represent the intercept is quite arbitrary, so it is perfectly acceptable to use - as we will for the remainder of this article - the equation in the form y = m x + b as b is a less commonly used symbol. Indeed, this is the form of the equation routinely used in some other countries and several variations are used around the world.¹

Paul Yates discusses tips for teaching gradient in chemical calculations