Experiment 1: Penny Density, Unit Conversions, and Reaction Temperature Effects Save

Unit Conversions

You'll measure volume in mL and cm³, mass in grams, sometimes convert to kg.

Important conversions in this lab

1 mL = 1 cm³, 1000 g = 1 kg, 1 cm = 10 mm, K = °C + 273.15.

Density

Penny density is found by measuring mass on a balance and volume by water displacement.

Density formula

ρ = m/V.

Density units

g/cm³ or g/mL.

Penny density comparison

You'll compare penny density to pure Cu (8.95 g/cm³) and Zn (7.14 g/cm³).

Pennies before 1982

Before 1982: ~95% Cu, heavier, mass ≈ 3.10 g.

Pennies after 1982

After 1982: Mostly Zn core with thin Cu layer, lighter, mass ≈ 2.50 g.

Statistical Analysis

You will calculate: Mean (average) penny mass or density, Range: max - min, Standard deviation (s): spread of data, Error of the mean: s/n.

Purpose of statistical analysis

Decide if two sets of pennies are statistically different.

Graphing

You'll make graphs like penny mass vs. year.

Identifying trends

Expect to identify trends (step change in 1982).

Glow stick discussion

Bending = mixes chemicals → reaction begins.

Higher temperature effect on glow sticks

Higher T = faster reaction, brighter but shorter glow.

Lower temperature effect on glow sticks

Lower T = slower reaction, dimmer but lasts longer.

Density calculation example

A penny weighs 2.51 g. Its volume is 0.340 cm³. What is its density?

Cu percentage calculation example

A pre-1982 penny weighs 3.09 g. If its volume is 0.340 cm³, what % of Cu is in the penny (Cu density = 8.95 g/cm³, Zn density = 7.14 g/cm³)?

Mean, range, and standard deviation calculation example

Six pennies have masses: 3.08, 3.10, 3.11, 3.09, 3.07, 3.12 g. Calculate the mean, range, and standard deviation.

Water density change with temperature

When you heat water, does its density increase or decrease? Why?

Floating solid conclusion

If you place a solid in water and it floats, what can you conclude about its density?

Evidence of chemical reaction in glow sticks

What physical evidence shows that glow sticks involve a chemical reaction?

Density of Cu vs Zn

Cu = 8.95 g/cm³, Zn = 7.14 g/cm³.

Major change in pennies 1982

They changed from mostly copper to zinc with a thin copper coating.

Average mass of a pre-1982 penny

~3.10 g.

Average mass of a post-1982 penny

~2.50 g.

Standard deviation measurement

The spread of data around the mean.

Error of the mean significance

How well your mean represents the 'true' value (smaller = better).

Glow stick brightness in hot water

Higher temperature increases reaction rate.

Glow stick duration in cold water

Lower temperature slows down the reaction rate.

Signs of a chemical reaction

Color change, gas formation, precipitate formation, temperature/light change.

Weight difference in pre-1982 pennies

They have more copper (higher density).