Science Fair

Grown-ups

Which grows crystals faster: salt or sugar?

4th–8th grade · 5 days of testing · free · ages 9 to 14 · 30 minutes a sitting

  • 🔥 Hot
  • 👶 Small parts
  • 🚫 Test food is not for eating
What you need for the salt and sugar crystals project: salt, sugar, hot water from the tap or kettle, for a grown-up to pour, a clear jar or tall glass, string or yarn

My hypothesis

If I change what is dissolved in the water, then how long the longest crystal is after five days will ______, because ______.

You fill in the blanks. Think about what happens to the water in the jar over five days, and where the salt or sugar has to go. A guess is a good because: the test finds out.

Change, measure, keep the same

CHANGE

what is dissolved in the water: Salt, Sugar, Nothing (just water)

MEASURE

how long the longest crystal is after five days, in mm

KEEP THE SAME

  • the same amount of hot water
  • the same kind of string
  • the same quiet shelf, out of the sun

Scientists call the thing you change the independent variable and the thing you measure the dependent variable. The things you keep the same are the controls: if one of them changed too, you wouldn't know which change made the difference. Try each of the 3 levels 3 times.

What you need

  • Salt: about 1 cup
  • Sugar: about 4 cups
  • Hot water from the tap or kettle, for a grown-up to pour: 1 cup for each jar
  • A clear jar or tall glass: 9 clear jars, three for each
  • String or yarn
  • A pencil: 9
  • Paper clips: 9
  • A measuring cup
  • A spoon
  • 📏 A ruler

Steps

  1. Grown-up: A grown-up pours one cup of hot water into each of the nine jars.
  2. Grown-up: A grown-up stirs salt into three jars, a spoon at a time, until no more disappears.
  3. Grown-up: A grown-up stirs sugar into three more the same way. The last three are just water.
  4. Tie a string to each pencil, hang a paper clip on the end, and lay the pencils across the jars.
  5. Leave the jars on a quiet shelf where nobody will bump them.
  6. Every day for five days, measure the longest crystal on each string.
  7. Write each day's number in your logbook, and draw what you see.
  8. On day five, put the final lengths in your results table.
  9. Draw a line graph: days along the bottom, crystal length up the side.

3 steps are a grown-up's, marked above. Write each number down straight away, in the table below, so nothing is lost.

Your results table

MY RESULTSPeabody 🦉 peabody.kids/science-fair

Name ______________________ Fair day ____________

Question: Which grows crystals faster: salt or sugar?

I changed: Dissolved in the jar   I measured: how long the longest crystal is after five days (mm)

Dissolved in the jarTry 1 (mm)Try 2 (mm)Try 3 (mm)Mean
Salt
Sugar
Nothing (just water)

MY GRAPH (a line graph: dissolved in the jar along the bottom, mm up the side)

What I noticed: ______________________________________________

From 4th grade, add the tries for each level and divide by how many there were: that's the mean, and it goes in the last column. Then draw a line graph, because the thing you change is a number that goes up.

📊 Make my graph🖨 Print the whole packet (9 pages)

Why it works

Hot water can hold more salt or sugar than cold water can. As the water cools and slowly dries up, it can't hold it all, and the extra comes out as crystals on the string. Salt and sugar make different shapes of crystal, little cubes and long slanted blocks, and they come out at different speeds, which is what your test measures.

Going further (7th and up): Change a second thing: grow salt crystals in a warm spot and a cool spot, and graph each day's length for both.

Board layout

MY BOARD · 36 × 48 in tri-foldPeabody 🦉 peabody.kids/science-fair
  1. ❓ Question (10 × 8 in): Which grows crystals faster: salt or sugar?
  2. 💭 Hypothesis (10 × 9 in): If I change what is dissolved in the water, then how long the longest crystal is after five days will ______, because ______.
  3. 🧺 Materials (10 × 12 in): 9 things: see your list.
  4. 🪜 Steps (22 × 9 in): 9 steps, three tries at each level.
  5. 📊 Results (22 × 16 in): Your table (Dissolved in the jar down the side, tries across) and your line graph.
  6. ✅ Conclusion (10 × 14 in): My hypothesis was right / partly right / not right. I know because…

Materials to list: Salt; Sugar; Hot water from the tap or kettle, for a grown-up to pour; A clear jar or tall glass; String or yarn; A pencil; Paper clips; A measuring cup; A spoon.

Bring photos or drawings of your test. Nothing wet, hot, powered or alive on the table.

This project at your grade

4th–6th gradeTries: three at each level. The table: units in the header and a mean column. The graph: a bar graph, or a line for a number that grows. The conclusion: right, partly or not, and the numbers that show it.
7th grade and upTries: three or more at each level. The table: a mean for every level of both tests. The graph: a graph with two lines or two sets of bars. The conclusion: the numbers, what might have gone wrong, and a next question. Second variable: grow salt crystals in a warm spot and a cool spot, and graph each day's length for both.

Every grade this project fits works out a mean. See every project for 4th grade, or print a blank results table.

What a judge will ask

  • What did you change, and what did you measure? I changed what is dissolved in the water and measured how long the longest crystal is after five days, in mm.
  • What did you keep the same, and why does that matter? I kept the same amount of hot water and the same kind of string the same, so the only difference was what is dissolved in the water.
  • How many times did you test it? 3 times at each of my 3 levels.
  • If you did it again, what would you change or test next? I'd grow salt crystals in a warm spot and a cool spot, and graph each day's length for both.

Make it yours

Keep this project on this device and Peabody counts down to your fair day, with a plan for each day. Nothing is sent anywhere.

Try next

👨‍👩‍👧 For grown-ups and teachers: how much to help, the safety rules, and running a school fair. Science fair v0.16.1 · Checked .

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