Matter, Properties, Classification & Commercial Products
Who proposed that matter is made of tiny, indivisible particles called atomos?
Democritus
In which state of matter do particles mainly vibrate in fixed positions?
Solid
What do we call a combination of two or more substances that are physically combined?
Mixture
What term describes how close a measured value is to the true or accepted value?
Accuracy
Which ancient Greek thinker believed that water was the basic substance of everything?
Thales
Why does a gas expand to fill its container?
Its particles move rapidly and randomly, spreading throughout the available space.
What is the SI unit of weight?
Newton (N)
What type of mixture has visibly distinguishable components or different phases?
Heterogeneous mixture
A student measures the mass of an object five times and obtains 12.4 g, 12.5 g, 12.4 g, 12.5 g, and 12.4 g. What quality do these measurements demonstrate, and how can it be determined mathematically?
Precision. The range is 12.5−12.4=0.1 g1indicating that the measurements are close to one another.
According to Dalton, what happens to atoms during a chemical reaction?
Atoms are rearranged, combined, or separated, but are not created or destroyed in ordinary chemical reactions.
A material has a mass of 120 g and a volume of 40 cm³. What is its density?
3 g/cm³
What type of mixture has a uniform composition throughout?
Homogeneous mixture or solution.
What separation method allows a liquid to be poured off after heavier solid particles settle at the bottom?
Decantation.
A thermometer consistently reads 3°C higher than the actual temperature. What type of error is present, and what should be done to correct it?
Systematic error. The thermometer should be calibrated to correct its consistent measurement bias.
Which law states that a pure compound always contains the same elements in the same fixed proportions by mass?
Law of Constant Composition (Law of Definite Proportions).
Why is water (H₂O) classified as a compound rather than a mixture?
Hydrogen and oxygen are chemically bonded in a fixed ratio.
Why are cleaning products formulated with specific chemical substances?
To perform particular cleaning functions, such as dissolving grease, removing stains, or killing microorganisms.
A student wants to recover salt from saltwater by removing the water through heating. What separation method should be used?
Evaporation.
A student obtains a measured value of 48.6 g for an object whose actual mass is 50.0 g. Calculate the percentage error and express your answer to three significant figures.
2.80%
In Rutherford's gold foil experiment, most alpha particles passed straight through the foil. What did this observation reveal about the atom?
Most of the atom is empty space.
Why is density classified as an intensive property while mass is extensive?
Density does not depend on the amount of substance, while mass does.
What happens to the kinetic energy and motion of particles when a substance is heated?
Their average kinetic energy increases, causing them to move faster.
A student is given a mixture containing salt, sand, and iron filings. The student first uses a magnet to remove the iron filings, then adds water to the remaining mixture and filters it. After filtration, the student heats the filtrate until all the water evaporates.
Question: Explain why each separation method works and identify the physical property of each substance that makes the separation possible.
Magnetic separation: Iron filings are attracted to a magnet because of their magnetic properties.
Filtration: Sand is insoluble in water, so its particles are trapped by the filter paper while dissolved salt passes through with the water.
Evaporation: Water evaporates when heated, leaving the dissolved salt behind because salt has a much higher boiling point and does not evaporate under these conditions.
A student measures an object and gets 9.8 cm, 9.9 cm, and 9.8 cm. The actual length is 10.0 cm. What is the range of the measurements, and are the results more precise or accurate?
Range: 9.9−9.8=0.1 cm
Conclusion: The measurements are precise because they are close to one another and reasonably accurate because they are close to the actual length.
A neutral atom has a mass number of 40 and contains 22 neutrons. Determine its number of protons, electrons, and atomic number. Then identify the element.
Protons: 40−22=18
Electrons: 18 (because the atom is neutral)
Atomic number: 18
Element: Argon (Ar)