LAB:

Uses water, soap, plastic pipets, pennies, paper cups, and paper towels

Which of the following is the best safety precaution for this lab?

• Wear safety goggles and lab coat when available

• Handle water carefully to avoid spills
• Never put lab materials in your mouth
• All of the above

Answer explanation

All of the above options contribute to ensuring safety during the lab.

If water spills during the lab, what should you do first?

• Continue the experiment and clean later
• Tell the teacher and clean it up immediately
• Call 911
• Ignore it if it’s a small spill

Answer explanation

Promptly informing the teacher and cleaning up ensures safety and prevents hazards.

Soap is safe to handle in this lab without gloves.

• True
• False

Answer explanation

Soap is generally safe to handle without gloves in this context, as it’s non-toxic.

The question in the lab was:

"How does adding a drop of soap to water affect the number of drops of water that can stay on the surface of a penny?"

What is the manipulated (independent) variable in this experiment?

Answer explanation

The manipulated variable is what the experimenter changes, in this case, adding soap.

Tags

NGSS.MS-PS1-2

The question in the lab was:

"How does adding a drop of soap to water affect the number of drops of water that can stay on the surface of a penny?"

What is the responding (dependent) variable in this experiment?

Answer explanation

The responding variable is what is measured, here the number of water drops.

Hypothesis:
"The water with soap will increase the number of drops the penny can hold."

Is this a testable hypothesis?

• Yes, because it makes a prediction that can be measured
• No, because it is just an opinion

Answer explanation

A testable hypothesis allows for measurable outcomes, which this hypothesis provides.

Which of the following would be considered controlled variables? (Select all that apply)

• Same type of penny used
• Same type of dropper
• Same starting temperature of water
• Number of students in the group

Answer explanation

Controlled variables are kept constant to ensure a fair test, excluding group size.

Tags

NGSS.MS-PS2-2

Why should you repeat the trials 10 times for each group?

• To make the lab longer
• To reduce errors and get more reliable data
• To use up all the water
• To test more students’ skills

Answer explanation

Repeating trials improves data reliability by reducing the impact of errors.

Tags

NGSS.MS-ETS1-4

A​​ (a)   Variable is a factor in an experiment that changes.

A​ (b)   variable is a factor changed by the experimenter.

A ​ (c)   variable is a factor that stays the same for all trials.

(memory tool: "DRY MIX" )

• Random 
• Responding
• Manipulated
• control

Answer explanation

Variables in a scientific investigation can be graphed.

As the X changes, the Y is affected.

In your own words, explain why adding soap might change the number of drops a penny can hold.

(key words: Surface Tension and Cohesion)

Answer explanation

Adding soap reduces water’s surface tension, allowing fewer drops to stay on the penny.