Mad Science!
If we dissolved salt in water, what would happen to the volume?
The total volume was less than the sum of the salt volume plus the water volume
What is the purpose of creating histograms from class data?
To find patterns and trends that are difficult to see in individual experiments
Define a closed system.
A system where nothing can enter or leave
State the Law of Conservation of Mass.
In a closed system, mass is conserved—it stays exactly the same. Mass is neither created nor destroyed.
You leave a cup of water on the counter for a week. The water level goes down. Where did the mass go?
The water evaporated into the air. The mass didn't disappear—it went from liquid in the cup to water vapor in the air. This is an open system.
What did we wipe off the outside of our containers in the ice-water experiment, and why?
Condensation (water from the air). We wiped it off to maintain a closed system so no mass was added from outside.
Our balance has a sensitivity of ±0.02 g. If most data points cluster between -0.02 g and +0.02 g, what does this tell us?
The variations are within the measurement uncertainty of the balance, so there's no actual mass change—just the limits of our instrument's accuracy and/or precision
Give two examples of things we did in our experiments to create closed systems.
(1) Used sealed/capped containers, (2) Wiped condensation off the outside, (3) Capped test tubes immediately after reactions, (4) Measured everything inside the container
Why is mass a better measure of matter than volume?
Mass is conserved during physical and chemical changes, while volume can change. This makes mass a reliable, fundamental measure of the amount of matter present
A candle loses mass as it burns. Does this violate conservation of mass? How did the candle lose mass?
No. Burning is a chemical reaction with oxygen. The wax combines with oxygen to form CO₂ and water vapor that escape into the air. If you captured all the gases and measured them plus the oxygen used, the total mass would equal the original candle mass.
In the copper and sulfur experiment, why did we cap the test tube before heating?
To trap any gases produced by the reaction and prevent mass from escaping (keeping it a closed system)
Why is combining data from the whole class better than relying on just your own single measurement?
Crowdsourcing data helps reveal true patterns and reduces the impact of random errors from any single measurement. Repeating experiments increases confidence in results
Burning wood in a fireplace is an open system. Explain what leaves the system and why the mass appears to decrease.
Carbon dioxide gas and water vapor escape up the chimney. The mass appears to decrease because we only measure the ash left behind.
Can the Law of Conservation of Mass ever be absolutely proven? Why or why not?
No. We can't test every possible situation that has ever happened or will ever happen. We can only gain very high confidence based on thousands of experiments, but we can't prove it holds under all conditions we haven't tested yet.
A student measures 50.00 g of ice, lets it melt in an open container, then measures 49.87 g of water. They conclude mass is not conserved. What's wrong with this conclusion?
This was an open system. Some water likely evaporated during melting, or there could be measurement error. The 0.13 g difference is small and could be within experimental error. To properly test conservation, they need a sealed container.
What gas was produced in the Alka-Seltzer experiment, and how do we know the mass didn't change even though gas was produced?
Carbon dioxide (CO₂) was produced. The mass didn't change because it was produced in a closed container/system, so the gas couldn't escape.
One group accidentally used twice as much copper and sulfur as instructed. Where would their result appear on the histogram?
If there were any mass change (which there shouldn't be in a closed system), doubling the materials would not double the change. Any measured should still be close to zero if properly sealed.
A sealed terrarium has plants, soil, and air inside. Is this a closed system? Will the mass change over time?
Yes, it's a closed system because the seal prevents matter from entering or leaving. The mass will not change over time even though plants grow, decompose, and photosynthesize—the matter just cycles between different forms (CO₂, water, plant tissue, soil)
Scientists have tested conservation of mass with precision to one part in a billion. Represent a billionth as a decimal.
0.000 000 001
Batteries lose mass over time even when not in use. Gasoline evaporates from a sealed tank. Are these violations of conservation of mass? Explain both cases.
Batteries: No violation. Slow chemical reactions occur even when not in use, producing gases that can escape. Sealed gas tank: This seems like a closed system, but gas tanks have vents to prevent pressure buildup, making it an open system where gasoline vapors can escape. Neither violates conservation—both are open systems.
A student left their sugar-water mixture uncapped overnight. The next day, the mass decreased by 0.45 g. Explain why this doesn't violate conservation of mass.
This was an open system (uncapped). Water evaporated into the air, so the mass left the container. The total mass of the system (container + air) stayed the same—the water just moved from liquid in the container to vapor in the air.
If we used bucket sizes of 0.001 g instead of 0.01 g on our histogram, what would happen to the pattern? Explain using the concept of balance sensitivity.
There would be too many bins for our instrument, hiding the pattern in noise.
Steel wool gains mass when it rusts in open air. Does this violate conservation of mass? Explain what would happen if we rusted steel wool in a sealed container sitting on a balance.
No violation. Rusting is iron combining with oxygen from the air. In open air, oxygen enters the system, so mass increases. In a sealed container on a balance, the total mass wouldn't change because the oxygen reacting from inside the container would become part of the rust—mass just transfers from air to solid.
A student says "We measured mass changes of zero in our four experiments, so we proved conservation of mass is always true." Identify at two problems with this reasoning and explain what we can actually conclude from our experiments.
(1) Four experiments can't prove a universal law applying to all situations everywhere, (2) Our balance cannot detect changes smaller than ±0.003 g, (3) We only tested normal conditions, not extremes like nuclear reactions. Conclusion: We have high confidence mass is conserved in everyday changes, but this is strong evidence, not absolute proof.
In nuclear reactions (like in the sun), tiny amounts of mass actually do convert to energy following E=mc². Does this mean conservation of mass is wrong? How do scientists reconcile this?
Conservation of mass has limits at extreme conditions. Scientists use a more general principle: conservation of mass-energy. In everyday chemical reactions, the mass-to-energy conversion is so tiny we can't measure it, so conservation of mass works perfectly. But in nuclear reactions, the conversion is measurable. This shows that scientific laws can have boundaries—they work in certain domains but may need refinement at extremes