Worksheet Grade 8 Engineering & Design

Coppertine River Road Salt: A Scatter Plot and Trend-Line Worksheet

A grade 8 worksheet where students plot chloride against conductivity for a salted river, draw a line of best fit, and use its slope to predict values.

Grade: Grade 8
Subject: Engineering & Design
Material: Worksheet
Time: 40 min
Prep: No prep
Materials: Graph paper, Ruler, Calculator

Standards

8.SP.A.1 Common Core Math

Construct and interpret scatter plots for bivariate measurement data to investigate patterns of association between two quantities, describing clustering, outliers, and positive, negative, linear, or nonlinear association.

How this material aligns: Items 1 through 4 have students build a scatter plot of chloride and conductivity and describe the association and any outliers, exactly the scatter-plot reading this standard names.

All materials for 8.SP.A.1 →

8.SP.A.2 Common Core Math

Know that straight lines are widely used to model relationships between two quantitative variables. For scatter plots that suggest a linear association, informally fit a straight line and assess the model fit by judging the closeness of the data points to the line.

How this material aligns: Items 5 through 7 have students draw a line of best fit, estimate its slope from two points, and use it to predict, the trend-line work this standard requires.

All materials for 8.SP.A.2 →

MS-ESS3-3 NGSS

Apply scientific principles to design a method for monitoring and minimizing a human impact on the environment.

How this material aligns: Item 8 has students use the chloride-conductivity pattern to explain how tracking conductivity can flag rising road-salt pollution, connecting the data to monitoring a human impact on the environment this standard describes.

All materials for MS-ESS3-3 →

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This material is in the public domain (CC0) and may be copied, edited, and shared freely, without attribution. Updated 2026-07-23.

Objectives

Students will build a scatter plot and describe the association between two water-quality measurements.
Students will draw a line of best fit, estimate its slope, and use it to predict a value.

Vocabulary

Key words: scatter plot, association, line of best fit, slope, chloride

Teacher overview

Road salt used on winter roads washes into nearby streams, where it raises the chloride level and makes the water carry electricity more easily. This worksheet uses a fictional set of samples from Coppertine River so students can see that link as a scatter plot. Students plot the points, describe the pattern, draw a line of best fit, and use its slope to predict a value. The task also connects the math to why crews track chloride after a salty winter.

Coppertine River Road Salt: A Scatter Plot and Trend-Line Worksheet — Grade 8 Engineering & Design

Name: ____________________________ Date: ______________

Student Worksheet

Suppose a class tested Coppertine River, a fictional river, at eight spots after winter road salting. At each spot they measured the chloride level (in mg/L) and the conductivity (a measure of how well the water carries electricity, in microsiemens per centimeter, uS/cm). The data are below.

Chloride (mg/L)	Conductivity (uS/cm)
20	175
40	250
60	330
80	400
100	500
120	560
140	660
160	720

Make a scatter plot of the eight points. Put chloride on the x-axis and conductivity on the y-axis.
Does the plot show a positive, negative, or no association?
Is the pattern roughly linear or nonlinear?
Are there any clear outliers, meaning points far from the pattern? Name one or write "none."
Draw a line of best fit through the points. Pick two points on your line and estimate the slope.
In one sentence, explain what the slope means for chloride and conductivity.
Use your line of best fit to predict the conductivity when chloride is 90 mg/L.
Higher chloride from road salt can stress freshwater life. Using the pattern, explain what happens to conductivity as more road salt washes into the river.

From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.

Answer Key

Answer: A correct scatter plot of the eight points.
Points rise from lower left to upper right: (20, 175), (40, 250), (60, 330), (80, 400), (100, 500), (120, 560), (140, 660), (160, 720). Check that chloride is on the x-axis and conductivity on the y-axis.
Answer: Positive association.
As chloride goes up, conductivity also goes up, so the association is positive.
Answer: Roughly linear.
The points climb at a steady pace and stay close to a straight path, so the pattern is roughly linear.
Answer: None.
No point sits far off the rising pattern, so there is no clear outlier. Accept a student who flags a point slightly off the line if they explain their reasoning.
Answer: about 4 uS/cm per mg/L.
A good line of best fit runs near y = 4x + 90. Using two points on that line, such as (20, 170) and (160, 730), slope = (730 minus 170) divided by (160 minus 20) = 560 divided by 140 = 4. Accept any slope from about 3.5 to 4.5.
Answer: Conductivity rises about 4 units for each extra 1 mg/L of chloride.
The slope means every added 1 mg/L of chloride raises conductivity by roughly 4 microsiemens per centimeter.
Answer: about 450 microsiemens per centimeter.
Using y = 4x + 90 with x = 90: y = 4 x 90 + 90 = 360 + 90 = 450. Accept any prediction from about 420 to 480 read off a reasonable line.
Answer: Conductivity rises as road salt rises.
More road salt raises the chloride level, and the positive pattern shows conductivity climbing right along with it, which is why crews can track salt pollution by watching conductivity.

Differentiation

Support

Provide graph paper with the axes already drawn and labeled and the scale marked, so students only plot points. Model plotting the first two points together, and give a clear plastic ruler for the line of best fit.

Extension

Ask students to find the equation of their own line of best fit in the form y = mx + b, then compare their predicted conductivity at 90 mg/L with a classmate's line and explain why the two predictions differ.

ELL supports

Pre-teach scatter plot, association, and slope with a simple picture showing points and a rising line. Provide sentence frames: "The association is ___" and "As chloride goes up, conductivity goes ___."