Anything that occupies space and has mass is called matter.
Missing Word
matter
Matter is the general term for anything that has mass and takes up space, from air to rock. Chemistry studies the composition, properties and changes of matter.
Category: Classification of Matter
Question 2
In the solid state, particles are packed closely in fixed positions, giving the sample a definite shape and volume.
Missing Word
solid
A solid holds its own shape because its particles are locked tightly together and can only vibrate in place. Liquids flow and gases expand because their particles can move past each other.
Category: States of Matter
Question 3
A homogeneous mixture such as salt fully dissolved in water is called a solution.
Missing Word
solution
A solution is a homogeneous mixture, meaning its composition is uniform throughout. Salt water, air and vinegar are common examples.
Category: Classification of Matter
Question 4
Brass, a homogeneous mixture of the metals copper and zinc, is an example of an alloy.
Missing Word
alloy
An alloy is a homogeneous mixture of metals, or of a metal with another element, with a uniform composition. Because the proportions can vary, an alloy is a mixture rather than a compound.
Category: Classification of Matter
Question 5
Gold, a pure substance that cannot be broken down into simpler substances by chemical changes, is an element.
Missing Word
element
An element is a pure substance that cannot be decomposed by chemical changes. Gold, oxygen and carbon are elements, while water is a compound that can be broken down.
Category: Classification of Matter
Question 6
Mass is an extensive property because its value grows as the sample gets larger.
Missing Word
extensive
An extensive property depends on the amount of matter present, as mass and volume do. Intensive properties, by contrast, are the same for any size sample.
Category: Physical and Chemical Properties
Question 7
Temperature is an intensive property, so a cup of hot coffee and a spoonful taken from it have the same value.
Missing Word
intensive
An intensive property does not depend on the size of the sample. Temperature, density and boiling point are intensive, while mass and volume are extensive.
Category: Physical and Chemical Properties
Question 8
The ratio of an object's mass to its volume is its density.
Missing Word
density
Density is mass per unit volume and is often reported in g/mL for liquids or g/cm3 for solids. It is a physical property that can help identify a substance.
Category: Physical and Chemical Properties
Question 9
The force that gravity exerts on an object is its weight.
Missing Word
weight
Weight is a force that depends on the strength of gravity, so it changes with location. Mass, the amount of matter, does not change from place to place.
Category: SI Units and Prefixes
Question 10
The SI base unit of temperature is the kelvin, whose scale begins at absolute zero.
Missing Word
kelvin
The kelvin is the SI base unit of temperature, and its scale has no negative values because 0 K is absolute zero. It is written without a degree sign.
Category: SI Units and Prefixes
Question 11
The SI base unit of time is the second.
Missing Word
second
The second is the SI base unit of time, defined by the frequency of radiation from cesium atoms. Minutes and hours are larger units derived from it.
Category: SI Units and Prefixes
Question 12
The metric prefix micro represents a factor of one millionth.
Missing Word
micro
Micro- means 10^-6, so 1 microgram is one millionth of a gram. Milli- (10^-3) and nano- (10^-9) are the neighboring common prefixes.
Category: SI Units and Prefixes
Question 13
One cubic decimeter of volume equals exactly one liter.
Missing Word
liter
A liter is defined as the volume of a cube 10 cm on a side, which is one cubic decimeter. It is not an SI base unit but is widely used for volume in chemistry.
Category: SI Units and Prefixes
Question 14
How close a measured value is to the true or accepted value describes its accuracy.
Missing Word
accuracy
Accuracy compares a measurement with the true value, while precision describes how closely repeated measurements agree with one another. A set of results can be precise without being accurate.
Category: Accuracy and Precision
Question 15
A well-tested explanation of why nature behaves as it does, supported by a large body of experimental evidence, is a theory.
Missing Word
theory
A theory explains observations and has survived extensive testing, though it can still be revised if new evidence contradicts it. A law describes what happens, and a hypothesis is a tentative explanation not yet well tested.
Category: Scientific Method