Module 3A: Getting the Equation for a Straight Line
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Module 3B1: Getting the Equation for a Straight Line
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 = 0.15x + 0.1
well done
incorrect.Choose two points on the line, say (2, 0.4) and (12, 1.9)The slope is (1.90.4)/(122) = 0.15The yintercept is y  mx = 0.4  0.15x2 = 0.1
Following on from question 1, if the reading of an unknown sample was 1.2, estimate its concentrationCalcium concentration of unknown sample = 7.3 μM
well done
incorrect Rearrange the equation to make x the subjectx = (y  0.1)/0.15substitute in y = 1.2x = 1.1/0.15 = 7.3 μMtwo significant figures are justified here.
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 = 0.085x + 6.4
well done
incorrectChoose two points on the linesay (10, 5.55) and (20, 4.7)the slope is = (5.554.7)/(1020)= 0.85/10=0.085the y intercept is 5.55  (0.085x10)=5.55 + 0.85=6.4the equation is y = 0.085x + 6.4
Following on from the previous question, if the value for y = 4.8, what is the corresponding value for x?x = 19 (two significant figures is appropriate here)
well done
incorrectthe equation is y = 6.4  0.085xrearrange to make x the subjectx = (y6.4)/0.085substitute in for y = 4.8x = (4.86.4)/0.085x = 18.8 = 19 to 2 significant figures