Which kitchen liquid cleans an old penny best?
- 👶 Small parts
- 🚫 Not food
- 🧼 Wash your hands after
- 🚫 Test food is not for eating
My hypothesis
If I change the liquid the pennies soak in, then how many of the five pennies look shiny will ______, because ______.
You fill in the blanks. Think about what makes a penny dull, and which of these liquids might break it down. A guess is a good because: the test finds out.
Change, measure, keep the same
CHANGE
the liquid the pennies soak in: Vinegar with salt, Lemon juice, Plain water, Soapy water
MEASURE
how many of the five pennies look shiny, in pennies shiny, of 5
KEEP THE SAME
- pennies that are all about as dull
- a quarter cup of liquid in every cup
- five pennies in each cup
- ten minutes of soaking
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 4 levels 3 times.
What you need
- Pennies: 60 dull ones, all about as dirty
- White vinegar
- Salt
- Lemon juice
- Water from the tap
- Dish soap
- Clear plastic cups, all the same size: 4
- A measuring cup
- Measuring spoons
- A spoon
- Paper towels
- A stopwatch or a kitchen timer
- Masking tape, to mark lines
Steps
- Label four clear cups with tape: vinegar and salt, lemon juice, plain water and soapy water.
- Stir one teaspoon of salt into a quarter cup of vinegar in the first cup.
- Pour a quarter cup of lemon juice into the second cup and a quarter cup of tap water into the third.
- Stir one drop of dish soap into a quarter cup of tap water in the fourth cup.
- Slide five dull pennies into each cup, and start the timer for ten minutes.
- Lift the pennies out with a spoon and lay them on a paper towel.
- Count the pennies that look shiny all over. Any brown left means not shiny.
- Write the count for each cup in your table.
- Do the whole test two more times, with fresh liquids and new dull pennies.
- Wash your hands, and never drink the liquids.
- Find the mean for each liquid, and draw a bar graph.
Every step is one you can do yourself, with a grown-up nearby. Write each number down straight away, in the table below, so nothing is lost.
Your results table
Name ______________________ Fair day ____________
Question: Which kitchen liquid cleans an old penny best?
I changed: Liquid I measured: how many of the five pennies look shiny (pennies shiny, of 5)
| Liquid | Try 1 (pennies shiny, of 5) | Try 2 (pennies shiny, of 5) | Try 3 (pennies shiny, of 5) | Mean |
|---|---|---|---|---|
| Vinegar with salt | ||||
| Lemon juice | ||||
| Plain water | ||||
| Soapy water |
MY GRAPH (a bar graph: liquid along the bottom, pennies shiny, of 5 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 bar graph, one bar for each thing you tried.
Name ______________________ Fair day ____________
Question: Which kitchen liquid cleans an old penny best?
If I change the liquid the pennies soak in, then how many of the five pennies look shiny will ________________, because _____________________________________________
| I CHANGE | I MEASURE | I KEEP THE SAME |
|---|---|---|
| Liquid: Vinegar with salt, Lemon juice, Plain water, Soapy water | how many of the five pennies look shiny (pennies shiny, of 5) |
|
What I think will happen, in my own words:
Name ______________________ Fair day ____________
Question: Which kitchen liquid cleans an old penny best?
| Date | What I did | What I saw | What I think |
|---|---|---|---|
Name ______________________ Fair day ____________
Question: Which kitchen liquid cleans an old penny best?
| Date | What I did | What I saw | What I think |
|---|---|---|---|
Name ______________________ Fair day ____________
Question: Which kitchen liquid cleans an old penny best?
| Date | What I did | What I saw | What I think |
|---|---|---|---|
Name ______________________ Fair day ____________
Question: Which kitchen liquid cleans an old penny best?
My hypothesis was ☐ right ☐ partly right ☐ not right.
I know because my numbers show:
What surprised me, or what might have gone wrong (7th and up):
Next time I would test:
Idea: Change a second thing: soak pennies in the best liquid for 2, 5 and 10 minutes, and draw a line of shiny pennies against time.
Why it works
A dull penny is covered with a thin brown layer, where the copper has joined with the air. Acids, like the ones in vinegar and lemon juice, can dissolve that layer, and salt helps the vinegar do it faster. Plain and soapy water mostly wash off dirt, so they usually leave the penny dull.
Going further (7th and up): Change a second thing: soak pennies in the best liquid for 2, 5 and 10 minutes, and draw a line of shiny pennies against time.
Board layout
- ❓ Question (10 × 8 in): Which kitchen liquid cleans an old penny best?
- 💭 Hypothesis (10 × 9 in): If I change the liquid the pennies soak in, then how many of the five pennies look shiny will ______, because ______.
- 🧺 Materials (10 × 12 in): 13 things: see your list.
- 🪜 Steps (22 × 9 in): 11 steps, three tries at each level.
- 📊 Results (22 × 16 in): Your table (Liquid down the side, tries across) and your bar graph.
- ✅ Conclusion (10 × 14 in): My hypothesis was right / partly right / not right. I know because…
Materials to list: Pennies; White vinegar; Salt; Lemon juice; Water from the tap; Dish soap; Clear plastic cups, all the same size; A measuring cup; Measuring spoons; A spoon; Paper towels; A stopwatch or a kitchen timer; Masking tape, to mark lines.
Bring photos or drawings of your test. Nothing wet, hot, powered or alive on the table.
This project at your grade
| 1st–3rd grade | Tries: three at each level (one is fine at a first fair). The table: levels and tries, numbers or pictures. The graph: a picture, or a simple bar graph. The conclusion: what happened, in their words. |
|---|---|
| 4th–6th grade | Tries: 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. |
From 4th grade up, the table gets a mean column. See every project for 2nd grade, or print a blank results table.
What a judge will ask
- What did you change, and what did you measure? I changed the liquid the pennies soak in and measured how many of the five pennies look shiny, in pennies shiny, of 5.
- What did you keep the same, and why does that matter? I kept pennies that are all about as dull and a quarter cup of liquid in every cup the same, so the only difference was the liquid the pennies soak in.
- How many times did you test it? 3 times at each of my 4 levels.
- If you did it again, what would you change or test next? I'd soak pennies in the best liquid for 2, 5 and 10 minutes, and draw a line of shiny pennies against time.
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
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