Worksheet

Two Sidewalk Carts, One Weight Mystery

Compare melting and mixing at two neighborhood science carts. Use scale readings, make a graph, and explain changes in total weight.

Grade 5ScienceInteractive · Printable

Aligned to5-PS1-2

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What’s included

Single worksheet
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1 NGSS standard
Printable answer key
14 questions
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Details

Format: Interactive · Printable
Grade: Grade 5
Subject: Science
Question types: Fill in the blank, Multiple choice, Circle the answer, Sorting, Short answer, Drawing

About this worksheet

What students practice

Students use scale readings to determine total weight before and after matter changes or is mixed.
Students graph before-and-after weights to show that total weight stays the same.
Students explain how leaving matter out of a measurement can make the measured weight seem to change.

How to use

Read the investigation and scale records together. Have students calculate totals, draw the graph, and use measured evidence to explain their conclusions.

Curriculum

NGSS standard covered

5-PS1-2

Measure and graph to show that the total weight of matter stays the same when it changes or is mixed.

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Two Sidewalk Carts, One Weight Mystery

Use scale readings and a graph to compare matter before and after changes.

1. Check the Measurements

Read about the two carts. Use the scale records to answer the questions. All weights are in grams (g).

Science Along the Sidewalk

During a neighborhood street fair, a science club sets up two carts near busy sidewalks. The Park Gate cart has sealed pouches of ice. The Metro Plaza cart has bottles of water and small cups of salt. Visitors will compare what happens to the total weight when ice melts and when salt mixes with water.

Each cart has a digital scale on a level, sheltered table. Before each trial, students place an empty tray on the scale and reset its reading to zero. The tray stays on the scale during each measurement. Its weight is not included in the recorded numbers. Students wait for the display to stop changing and record the reading to the nearest gram.

At Park Gate, an adult places ice in a pouch and seals it. Students weigh the closed pouch, including the ice and the pouch itself. They leave it at room temperature until the ice melts. Then they weigh the same closed pouch again. They do not open it or add anything. They check that no water has leaked onto the table.

At Metro Plaza, students first weigh a capped bottle of water. Next, they weigh a cup holding salt. An adult pours all the salt into the bottle and replaces the cap. The students gently swirl the bottle until no salt grains can be seen. They weigh the capped bottle together with the empty salt cup. Nothing is spilled or thrown away.

Each cart completes three trials with different starting amounts. The pouch weights include the pouch and everything inside it. The final mixing weights include the bottle, cap, mixture, and empty cup. The records below show the scale displays. Before comparing a mixing trial's starting and ending weights, students must combine its two starting readings.

Park Gate: melting trials
Trial 1 — Sealed pouch with ice: 120 g. Same sealed pouch after melting: 120 g.
Trial 2 — Sealed pouch with ice: 160 g. Same sealed pouch after melting: 160 g.
Trial 3 — Sealed pouch with ice: 200 g. Same sealed pouch after melting: 200 g.

Metro Plaza: mixing trials
Trial 1 — Capped bottle with water: 170 g. Cup with salt: 30 g. Final capped bottle and empty cup together: 200 g.
Trial 2 — Capped bottle with water: 210 g. Cup with salt: 30 g. Final capped bottle and empty cup together: 240 g.
Trial 3 — Capped bottle with water: 250 g. Cup with salt: 30 g. Final capped bottle and empty cup together: 280 g.

Record the scale measurement for the sealed pouch before melting in Trial 1: g.

Find the total starting weight in mixing Trial 1. Add the capped bottle with water and the cup with salt: g.

In Trial 2, how much greater was the total starting weight at Metro Plaza than at Park Gate? g greater.

Why do students include the empty salt cup in the final mixing measurement?

A. The empty cup replaces the weight of the salt that disappeared.
B. The empty cup makes the bottle weigh as much as the pouch.
C. The cup was part of the starting total and must still be counted.
D. The cup must be added because the scale did not count it earlier.

2. Graph and Compare

Use Trial 2 from both carts. Graph the total starting and ending weights, then look for a pattern.

Make a bar graph with four bars: Pouch Before, Pouch After, Mixing Before, and Mixing After. Use Trial 2 only. Add the two starting readings for the mixing trial. Start the weight axis at 0, label it Weight (g), and count by 40 g. Give your graph a title.

Which pattern should a correct Trial 2 graph show?

A. Each before-and-after pair has equal heights, but the mixing pair is taller.
B. Each after bar is shorter because changing matter reduces its weight.
C. All four bars have equal heights because total weight always stays the same.
D. The mixing after bar is shorter because the salt can no longer be seen.

Make a claim about total weight when the ice melted and when the salt mixed with water. Support your claim with the starting and ending totals from Trial 3 at both carts.

Select the TWO comparisons that show a change in appearance without a change in total weight.

In Trial 1, solid ice became liquid water, while the sealed pouch stayed at 120 g.In Trial 1, the final bottle and cup weighed more than the final pouch.In mixing Trial 1, salt grains stopped being visible, while the total stayed at 200 g.The final mixing total was greater in Trial 3 than in Trial 1.

3. Check New Claims and Tests

Use the investigation to explain unexpected readings and plan a new test. In these questions, all stated measurements are accurate.

After mixing Trial 3, a student removes the bottle cap and leaves it on the table. The bottle and empty cup now weigh 272 g. The cap weighs 8 g. What best explains the lower reading?

A. Mixing used up 8 g of salt inside the bottle.
B. Removing the cap made 8 g of water disappear.
C. The empty cup became 8 g lighter during mixing.
D. The measurement left out an object that weighs 8 g.

10.

A new mixing trial starts with a total of 240 g. During pouring, 10 g of the mixture spills into a separate dish. Only the capped bottle and empty salt cup are weighed afterward.

The final scale reading should be g. If the spilled mixture is also counted, the total weight is g. Do not count the weight of the separate dish.

11.

A visitor says, “If total weight stays the same, the pouch and the mixing materials must weigh the same as each other.” Which response uses Trial 3 correctly?

A. The visitor is right because every object must have the same total weight.
B. Each total stays the same: 200 g for the pouch, 280 g for mixing.
C. The visitor is right because the two starting totals must both become 280 g.
D. The totals differ because melting removes weight while mixing adds weight.

12.

Sort these final measurement plans. Decide whether each plan counts everything included in that trial's starting total. Do not count the tray.

Weigh the same sealed pouch after all its ice melts, with no leaks.Weigh the capped bottle and mixture, but leave the empty salt cup on the table.Weigh the capped bottle, all the mixture, and the empty salt cup together.Pour some water out of the melted-ice pouch, then weigh the pouch and remaining water.

Counts everything from the starting total	Leaves something out

13.

After mixing Trial 2, an adult adds 20 g of water. Nothing spills, and the same bottle, cap, and empty cup are included. Which prediction and explanation are best?

A. 240 g, because total weight cannot increase even when water is added.
B. 220 g, because the added water makes the salt mixture lighter.
C. 260 g, because the measured group now includes 20 g of added matter.
D. 280 g, because both the water and the bottle gain 20 g.

14.

The club plans to compare a flat sheet of paper with the same sheet crumpled into a ball. The flat sheet weighs 5 g. Describe how to use a scale to test whether crumpling changes its total weight. Tell what must stay the same and predict the final reading.