Lab / experiment Grade 3 Health & Consumer Science

Weighing the Water in Snacks: The Brambleigh School Drying Lab

A grade 3 health lab: students weigh cucumber, apple, bread, and crackers in grams, dry them for four days, and weigh again to find how much water each snack held.

Grade: Grade 3
Subject: Health & Consumer Science
Material: Lab / experiment
Time: 2 sessions, ~80 min total
Prep: Moderate prep
Materials: Kitchen scale that reads in grams and has a zero or tare button (1 per group, or 2 shared by the class), Paper plates (8 per group: 4 for drying and 4 clean ones for the final weighing), Half of a cucumber per group, sliced thin by the teacher, One apple per group, cored and sliced thin by the teacher, Four slices of bread per group (about 100 grams), About 35 plain saltine-type crackers per group (about one sleeve, or 100 grams), Marker for labeling plates, A dry, sunny windowsill or a wire cooling rack near a window for drying, Soap, a sink, and paper towels for handwashing, Grid paper for the bar graph (1 sheet per student)

Standards

3.MD.A.2 Common Core Math

Measure and estimate liquid volumes and masses of objects using standard units of grams (g), kilograms (kg), and liters (l). Add, subtract, multiply, or divide to solve one-step word problems involving masses or volumes that are given in the same units, e.g., by using drawings (such as a beaker with a measurement scale) to represent the problem.

How this material aligns: Students weigh four snacks in grams before and after drying, and in questions 3 and 4 they subtract masses given in grams to find how much water Room 9's cucumber and bread lost, which are one-step mass problems in the same unit.

All materials for 3.MD.A.2 →

3.MD.B.3 Common Core Math

Draw a scaled picture graph and a scaled bar graph to represent a data set with several categories. Solve one- and two-step 'how many more' and 'how many less' problems using information presented in scaled bar graphs.

How this material aligns: In question 5 students draw a scaled bar graph of Room 9's water lost for four snacks with one square for every 10 grams, and in question 6 they solve a how-many-more problem using that graph.

All materials for 3.MD.B.3 →

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This material is in the public domain (CC0) and may be copied, edited, and shared freely, without attribution. Updated 2026-09-24.

Objectives

Students will measure the mass of four snacks in grams before and after drying and find the grams of water each one lost.
Students will draw a scaled bar graph of water lost and solve a how-many-more problem from it.
Students will explain that fruits and vegetables hold a lot of water, and that the water left the food by evaporating into the air.
Students will explain why water-rich foods help on a hot day but do not replace drinking water.

Vocabulary

Key words: mass, gram, evaporate, hydrated, water-rich, scale

Teacher overview

The third graders at Brambleigh School, a fictional school used for this lab, are planning snacks for a hot-weather field day. The school nurse has told them that fruits and vegetables help keep a body hydrated, and the class wants to know how a solid food can hold water at all. In this two-day investigation, groups weigh cucumber, apple, bread, and crackers in grams, let the pieces dry in a sunny spot for four days, and weigh them again. The mass each snack loses is water that left the food and went into the air, the same evaporation step that dries a puddle, so the result shows which snacks carry the most water.

The misconception to name at the start is the belief that only drinks put water into the body and that a food which feels solid, such as an apple, holds little or no water. Most groups find that the cucumber and apple lose most of their mass while the crackers barely change, which gives students measured evidence that some foods are mostly water. Close with the second half of the health message so that the lab does not create a new misunderstanding: water-rich snacks add to the water a body takes in, but they do not replace drinking water, especially for a child who is running and sweating on a hot day.

Slice the cucumber and apple thin, about the thickness of a coin, so they dry in four days. A sunny windowsill in a dry room works well, and a wire cooling rack speeds drying because air reaches both sides. If the room is humid, point a small fan at the plates. Check the plates each day; if any food grows mold, throw that plate out yourself, away from students, and have that group use Room 9's sample data in the questions. Check for food allergies before the lab, and substitute a gluten-free cracker or leave out the bread where needed. Most groups will weigh close to 100 grams rather than exactly 100, and the subtraction works the same way with any starting number.

Weighing the Water in Snacks: The Brambleigh School Drying Lab — Grade 3 Health & Consumer Science

Name: ____________________________ Date: ______________

Procedure

Safety first. Do not eat or taste any food in this lab. Tell your teacher if you have a food allergy. Wash your hands with soap before and after you touch the food. Your teacher does all of the cutting.

Day 1

Step 1. Label the plates. Write your group name on four paper plates. Then write one snack on each plate: cucumber, apple, bread, and crackers.

Step 2. Zero the scale. Put the cucumber plate on the scale. Press the zero button. The scale should now read 0 grams, so it will weigh only the food.

Step 3. Weigh the cucumber. Lay cucumber slices on the plate one at a time. Stop when the scale reads close to 100 grams. Write the exact number in the Start column of your table.

Step 4. Weigh the other snacks. Do the same for the apple, the bread, and the crackers. Zero the scale with each new plate first. Tear the bread into small pieces. Break the crackers in half.

Step 5. Spread the pieces out. Lay the pieces flat in one layer so they do not touch. Set the four plates in the drying spot your teacher picked.

Step 6. Make a guess. Which snack do you think will lose the most grams? Write your guess under the table.

Days 2, 3, and 4

Step 7. Turn the pieces. Flip each piece over once a day so both sides dry. Look for fuzzy spots. Fuzzy spots are mold. If you see mold, do not touch or smell that plate. Tell your teacher.

Day 5

Step 8. Weigh again. Put a clean, empty plate on the scale and press zero. Move all of the cucumber pieces onto it. Write the number in the After drying column. Do the same for each snack, using a new clean plate each time.

Step 9. Find the water lost. For each snack, take away the After drying number from the Start number. The answer tells how many grams of water left the food. Write it in the Water lost column.

Step 10. Clean up. Throw all of the food away. Wipe the table. Wash your hands with soap.

Data & Analysis

Snack	Start (grams)	After drying (grams)	Water lost (grams)
Cucumber
Apple
Bread
Crackers

My guess from Day 1: ___

Answer these questions. Use your own table for questions 1 and 2.

Look at your Water lost column. Which snack lost the most grams of water?
All of your snacks got lighter while they dried. Where did the lost grams go?
Room 9 at Brambleigh did the same lab. Their cucumber weighed 100 grams at the start. After drying, it weighed 10 grams. How many grams of water did the cucumber lose?
Room 9's bread weighed 100 grams at the start. After drying, it weighed 70 grams. How many grams of water did the bread lose?
Each of Room 9's snacks weighed 100 grams at the start. After drying, the cucumber weighed 10 grams, the apple weighed 20 grams, the bread weighed 70 grams, and the crackers weighed 98 grams. On grid paper, draw a bar graph of how many grams of water each snack lost. Let each square stand for 10 grams. For the crackers, draw a very thin bar, because their loss is less than one square. How many squares tall is the bar for the apple?
Room 9's cucumber went from 100 grams down to 10 grams. Their bread went from 100 grams down to 70 grams. Use your graph from question 5. How many more grams of water did the cucumber lose than the bread?
It is a hot field day. Which snack would give your body more water, cucumber slices or crackers? Use the lab to explain.
Talia says, "I ate a lot of cucumber and apple, so I do not need to drink water at field day." Do you agree with Talia? Tell why or why not.

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: The cucumber, in most groups.
Accept whichever snack the group's own Water lost column shows as largest. The cucumber usually loses the most and the apple is close behind, while the crackers lose almost nothing. If the bread or crackers lost the most, check whether the scale was zeroed with the plate on it.
Answer: The water in the food evaporated into the air.
Accept answers saying the water dried out of the food and went into the air as water vapor. Do not accept answers saying only that the food got smaller, because shrinking does not explain where the lost grams went; the scale showed a loss of mass, and that mass was water leaving the pieces.
Answer: 90 grams.
Start minus after drying: 100 − 10 = 90. Check by adding back: 10 + 90 = 100.
Answer: 30 grams.
Start minus after drying: 100 − 70 = 30. Check by adding back: 70 + 30 = 100.
Answer: 8 squares.
The apple lost 100 − 20 = 80 grams. Counting by 10s to 80 takes 8 squares, the same as 80 ÷ 10 = 8. The finished graph shows the cucumber at 9 squares (90 grams), the apple at 8 squares (80 grams), the bread at 3 squares (30 grams), and a very thin crackers bar for 2 grams (100 − 98 = 2).
Answer: 60 grams.
The cucumber lost 100 − 10 = 90 grams and the bread lost 100 − 70 = 30 grams, so 90 − 30 = 60. On the graph, the cucumber bar is 6 squares taller than the bread bar, and 6 squares of 10 grams each is also 60 grams.
Answer: Cucumber slices.
Accept answers that use the data: the cucumber lost far more grams of water than the crackers, so it held much more water that the body could take in. The crackers lost almost nothing, which shows they held very little water.
Answer: No, Talia still needs to drink water.
Accept answers explaining that the lab showed cucumber and apple hold a lot of water, so they do help, but they do not give a body all the water it needs. On a hot day, running and sweating use up water, so Talia should drink water before, during, and after field day as well as eat water-rich snacks.

Differentiation

Support

Weigh the Day 1 snacks with these groups, or give them plates already weighed to about 100 grams, so their effort goes into reading the scale on Day 5 and finding the water lost. Provide a hundreds chart or an open number line for the subtraction in Step 9 and questions 3 and 4, and give them grid paper with the scale already marked in 10s up to 100 for question 5.

Extension

Have these students weigh one snack, such as the cucumber, every day from Day 1 to Day 5 and make a second scaled bar graph that shows its mass each day. Ask them which day it lost the most water and to suggest a reason, such as how wet the pieces were at the start compared with later in the week.

ELL supports

Pre-teach mass, gram, scale, evaporate, and water-rich with a real scale, a real cucumber slice, and a picture of a puddle drying in the sun. Label each plate with a picture of its snack as well as the word. Provide the sentence frames "The ___ lost ___ grams of water" and "I agree or disagree with Talia because ___," and accept answers to questions 7 and 8 given as a labeled drawing with one sentence.

Extensions

Ask the class to use its results to write a short field day snack list for the school nurse. The list should name three water-rich snacks from the lab or from home, such as cucumber, apple, or orange slices, and it should end with a reminder that everyone still needs water breaks on a hot day. Invite the nurse to read the list and to explain which snacks the school already serves on field days.