## Module 3B1: Getting the Equation for a Straight Line

1

The concentration of calcium in a solution can be determined by measuring the intensiy of light emitted in a flame photometer.

Given the following data, write the equation for the line.

 Concentration (μM) Reading 2 0.40 4 0.71 6 1.01 8 1.3 10 1.6 12 1.9

y = x +

well done

incorrect.

Choose two points on the line, say (2, 0.4) and (12, 1.9)

The slope is (1.9-0.4)/(12-2) = 0.15

The y-intercept is y - mx = 0.4 - 0.15x2 = 0.1

 2 Following on from question 1, if the reading of an unknown sample was 1.2, estimate its concentration Calcium concentration of unknown sample = μM well doneincorrect Rearrange the equation to make x the subject x = (y - 0.1)/0.15 substitute in y = 1.2 x = 1.1/0.15 = 7.3 μM two significant figures are justified here.Your answer has been saved.

3

Given the following data, find the equation for the line.

 x y 5 5.98 10 5.55 15 5.12 20 4.7 25 4.28 30 3.85

y = x +

well done

incorrect

Choose two points on the line

say (10, 5.55) and (20, 4.7)

the slope is = (5.55-4.7)/(10-20)

= 0.85/-10

=-0.085

the y intercept is 5.55 - (-0.085x10)

=5.55 + 0.85

=6.4

the equation is y = -0.085x + 6.4