[ CHEM1010 ] Matter and Measurements

Observation

In the scientific method, what is the term for gathering qualitative and quantitative data?

Hypothesis

What is defined as a tentative explanation for a specific observation?

To test the validity of a hypothesis.

What is the primary purpose of performing experiments in chemistry?

Solid, liquid, and gas

The three states in which matter typically exists are _____, _____, and _____.

Law

This summarizes a series of related observations.

Theory

This gives the underlying reasons for the observations.

Matter

Anything that has mass and occupies space. Examples: Air, desk, kettle, human body.

Solid

Which state of matter is characterized by having both a constant volume and a constant shape? This also has the highest density.

Constant volume and changing shape

How are the volume and shape of a liquid described?

Gas

Which state of matter has both a changing volume and a changing shape? Also having the lowest density.

Mixture

In the classification of matter, what is the result if the composition is variable?

Pure Substance

In the classification of matter, what is the result if the composition is not variable?

Element

A pure substance that cannot be separated into simpler substances is called an _____.

Compound

What is a pure substance called if it can be separated into simpler substances?

Heterogeneous Mixture

A mixture that is not uniform throughout. Example: Wet sand.

Homogeneous Mixture

A mixture that is uniform throughout. Example: Tea with sugar.

It is a pure substance that cannot be broken down into simpler substances.

Why is helium classified as an element?

It is a pure substance composed of molecules that can be separated into simpler substances (elements).

Why is pure water classified as a compound?

A change that alters only the state or appearance but not the chemical composition.

What defines a physical change in a substance?

They do not change their identity.

How do the identities of atoms or molecules change during a physical change?

The liquid water changes to gas, but the molecules remain composed of water (H2​O).

Why is the boiling of water considered a physical change?

The substance is transformed into a different substance with a new composition.

What occurs during a chemical change regarding the composition of a substance?

Iron atoms combine with oxygen molecules from the air to form a new substance, iron oxide.

Explain why the rusting of iron is a chemical change.

Decanting

Sand and Water; This is a a type of separation where carefully pouring off the water into another container is done.

Distillation

Mixture of Liquids;

• This is a process in which the mixture is heated to boil off the more volatile (easily vaporizable) liquid

• The volatile liquid is then recondensed in a condenser and collected in a separate flask

Filtration

Solid and Liquid; A process in which the mixture is poured through filter paper in a funnel

Physical Property

A property a substance displays without changing its composition. Examples: Odor, taste, color, melting point.

Chemical Property

A property a substance displays only by changing its composition via a chemical reaction. Examples: Flammability, corrosiveness.

Gasoline must undergo a chemical change (burning) to display this property.

Why is the flammability of gasoline considered a chemical property?

Phase Change

A change from one phase (state of matter) to another. There are 6 phase changes

Melting Point

The temperature at which a solid changes into a liquid is known as the _____.

Freezing Point

The temperature at which a liquid changes into a solid.

They are always equal (e.g., 0C for water).

How does the freezing point of a substance compare to its melting point?

Physical Change

Is dissolving sugar in water a physical or chemical change?

Energy

This refers to the capacity to do work.

Work

This is defined as the action of a force through a distance.

Total Energy

This is the sum of an object’s potential and kinetic energy. Energy of an object may be converted from one form to another.

Potential Energy

This is energy associated with position or composition.

Kinetic Energy

This is energy associated with motion.

Meter

What is the SI base unit for length?

Kilogram

What is the SI base unit for mass?

Second

What is the SI base unit for time?

Kelvin

What is the SI base unit for temperature?

Mole

What is the SI base unit for the amount of a substance?

Ampere

What is the SI base unit for electric current?

Candela

What is the SI base unit for luminous intensity?

Mass

A measure of the quantity of matter within the object.

Weight measures the gravitational pull on matter, while mass measures the quantity of matter.

How does the definition of weight differ from the definition of mass?

1000 grams

How many grams are in one kilogram (kg)?

10^3 (or 1000)

The metric prefix 'kilo-' represents a multiplier of _____.

kg/m^3

What is the standard SI unit for density?

g/mL or g/cm^3

What are the two most common units used for density in a laboratory setting?

The sample expands (volume increases).

When a sample of copper is warmed from room temperature to 95C, what physical change occurs to its volume?

Density decreases as temperature increases.

How does increasing the temperature generally affect the density of most substances?

1.4g/cm3

If a cube of sugar weighs 11.2g and has a volume of 8cm3, what is its density?

Divide by 1000

What operation is used to convert milligrams (mg) to grams (g)?

Multiply by 1000

What operation is used to convert liters (L) to milliliters (mL)?

Yes

Are all nonzero digits considered significant?

Yes

Are interior zeros (zeros between nonzero digits) significant?

No; they only serve to locate the decimal point.

Are leading zeros (zeros to the left of the first nonzero digit) significant?

They are always significant.

When are trailing zeros after a decimal point significant?

Yes

Are trailing zeros before a decimal point and after a nonzero number significant?

It is unclear if they are placeholders or measured values; scientific notation should be used instead.

Why are trailing zeros before an implied decimal point considered 'ambiguous'?

Countable numbers and numbers from a definition (unit conversion factors).

What are the two types of 'exact numbers' in chemistry calculations?

Accuracy

How close a set of measurements are to the true or accepted value.

Precision

How close a series of measurements are to one another (reproducibility).

To carry out unit conversions by using conversion factors.

What is the purpose of using dimensional analysis in chemistry?

The result carries the same number of sig figs as the factor with the fewest sig figs.

For multiplication or division, how is the number of significant figures in the result determined?

The result carries the same number of decimal places as the quantity with the fewest decimal places.

For addition or subtraction, how is the precision of the result determined?

Round up

What do you do if the leftmost digit being dropped is 5 or more?