Chem Exam 1

What primarily determines whether a substance is poisonous, according to toxicology?

Its dosage/concentration (the amount/concentration of the substance)

What is everything with measurable mass made up of?

Matter

In which state of matter are particles far apart and in constant random motion?

Gas

What is a molecule?

A collection of atoms chemically bonded together in characteristic proportions

Is mass and weight the same thing?

No — mass is the amount of matter (constant), while weight depends on gravitational force (Fg) and changes with location (e.g., lower on the Moon than Earth)

What is a hypothesis (per the scientific method)?

A proposed explanation or educated guess about a phenomenon that can be tested through observation and experimentation

What is NOT needed to formulate a hypothesis?

Designing an experiment to test the hypothesis is part of forming/testing it, but data analysis comes after — the key needs are: background research, a clear research question, and identifying variables/relationships

What is the primary purpose of an experiment?

To test a hypothesis

What does the Law of Conservation of Energy state?

The total energy of a closed system cannot be created or destroyed, only transferred

In an experiment testing how acidic, neutral, and basic water affect seed germination (all else held constant), what is the independent variable?

The type of water used (acidic, neutral, basic)

What is the most common graph type used in chemistry?

A scatter plot

On a properly made graph, where should the y-axis (and typically x-axis) start?

At zero — not starting at zero misrepresents the data

What is the modern, most widely used unit system?

The International System of Units (SI)

What is an SI derived unit?

A unit formed by combining SI base units through mathematical operations (e.g., m/s, g/mL)

What makes a number an "exact number" (vs. a measured number)?

It comes from counting or a defined relationship (not from a measuring tool) — e.g., 273.15 in K = °C + 273.15, or a count of people

Give an example of a qualitative observation.

A descriptive (non-numerical) observation, e.g., "a copper(II) sulfate solution is blue and transparent"

Give an example of a quantitative observation.

A numerical measurement, e.g., "the temperature was 99.5°F" or "the sample contained 0.9% uranium-235"

Why do scientists use significant figures when reporting measurements?

To accurately communicate the precision and limitation of the measuring tool

A scale reads exactly 2.00 g too high. Three measurements come out very close together (10.51, 10.52, 10.51 g). What does this represent?

Low accuracy, high precision

What is the difference between accuracy and precision?

Accuracy = how close a measurement is to the true/accepted value; Precision = how close repeated measurements are to each other

Define chemistry.

The study of the structure and properties (physical and chemical) of matter

What is the difference between matter and mass?

Matter is anything that has mass and occupies space; mass is a measurable property of matter

Can something have mass but not be matter?

No — having mass is a defining characteristic of matter

Can something be matter but have no mass?

No — matter has a measurable mass by definition

Is light matter? Why or why not?

No — light has no measurable mass

Is sound matter? Why or why not?

No — sound has no measurable mass

Is heat matter? Why or why not?

No — heat is the transfer of energy, which has no measurable mass

Is oxygen gas matter even though you can't see it?

Yes — it has mass and occupies space

A sealed bottle of water evaporates but stays trapped inside as vapor. Does the total mass change?

No — mass is conserved in a closed/sealed system; mass doesn't change during a phase change

Why do scientists use mass instead of size (volume) to compare the amount of matter in objects?

Objects of the same size can contain different amounts of matter; mass directly measures the amount of matter (related to density)

What is meant by "particle(s)" in chemistry?

Small units of matter, such as atoms, molecules, or ions

Why is every molecule made of atoms, but not every atom part of a molecule?

Molecules are defined as two or more atoms bonded together, but some atoms exist independently in nature (atomic elements)

Atoms combine to form ____, and substances made of only one type of atom are called ____.

molecules; elements

What are the three most common states of matter on Earth?

Solid, liquid, and gas

Describe the particle arrangement in a solid.

Tightly packed particles in fixed positions

Describe the particle arrangement in a liquid.

Particles close together but able to slide past one another

Describe the particle arrangement in a gas.

Particles far apart, moving freely

Which state of matter has particles that are farthest apart?

Gas

Why can liquids flow while solids generally cannot?

Liquid particles aren't packed as tightly as solids, so there's enough space for them to slide past each other

Rank solids, liquids, and gases by particle motion (least to most).

Solids < Liquids < Gases

Describe particle motion in a solid.

Particles vibrate in place

Describe particle motion in a liquid.

Particles slide around each other

Describe particle motion in a gas.

Particles move rapidly, randomly, and constantly

What information is needed to formulate a hypothesis?

Background research from reliable sources, a clear research question, identified variables and their potential relationships, and a designed experiment to test the hypothesis

How does a hypothesis become a theory?

After extensive testing (including peer review) through which it is consistently supported by empirical evidence

Can a scientific hypothesis be disproven?

Yes

Can a scientific theory be "proven"?

No — a theory is valid as long as evidence supports it and no evidence disputes it; it cannot be proven, only supported

How is "theory" used in everyday conversation vs. in science?

Colloquially it means a guess/speculation with no evidence; scientifically it's a well-supported explanation backed by extensive empirical evidence

Is "matter is conserved in chemical reactions" a law, principle, or theory?

Law — supported by mathematical expressions

Is "atoms exist and combine to form substances" a law, principle, or theory?

Principle — conceptually explains the nature of matter

Is "gas volume increases with temperature" a law, principle, or theory?

Law — supported by a mathematical equation

Is "living species change/evolve over time through natural selection" a law, principle, or theory?

Theory — built upon a collection of laws and principles

What is the unit name, abbreviation, and property measured for "g"?

Gram (g) — measures mass

What is the unit name, abbreviation, and property measured for "L"?

Liter (L) — measures volume

What is the unit name, abbreviation, and property measured for "m"?

Meter (m) — measures distance/length

What is the unit name, abbreviation, and property measured for "°C"?

Degree Celsius (°C) — measures temperature

What is the unit name, abbreviation, and property measured for "s"?

Second (s) — measures time

What is the abbreviation for kilogram?

kg

What is the abbreviation for kelvin?

K

What is the abbreviation for quart?

qt

What is the abbreviation for centimeter?

cm

What is the abbreviation for pound?

lb

How many sig figs does 0.0530 have?

3

How many sig figs does -8.0 have?

2

How many sig figs does 0.001 have?

1

How many sig figs does 2050 have?

3

How many sig figs does 300. have?

3

How many sig figs does 800500 have?

4

How many sig figs does 28.003 g have?

5

How many sig figs does 0.000057 m have?

2

How many sig figs does 890000000 km have?

2

How many sig figs does 4.50 x 10^6 kg have?

3

How many sig figs does 0.7005 L have?

4

How many sig figs does 19.0 °C have?

3

How many sig figs does 863 have?

3

How many sig figs does 2.4 x 10^30 have?

2

How many sig figs does 7.01 x 10^-5 have?

3

How many sig figs does 0.3 x 10^8 have?

1

How many sig figs does 0.1101 have?

4

How many sig figs does 4.0070 have?

5

How many sig figs does 20.0 have?

3

How many sig figs does 720 have?

2

How many sig figs does 301 have?

3

How many sig figs does 5010 have?

3

Do 51.00 kg and 510000 kg have the same number of sig figs?

No — 51.00 kg has 4 sig figs, 510000 kg has 2 (ambiguous trailing zeros)

Do 0.825 m and 0.00825 m have the same number of sig figs?

Yes — both have 3 sig figs

Do 0.000073 s and 7.30 x 10^4 s have the same number of sig figs?

No — 0.000073 s has 2 sig figs, 7.30 x 10^4 s has 3

Do 480.0 L and 0.0480 L have the same number of sig figs?

Yes — both have 4 sig figs

Do 0.00575 g and 5.75 x 10^-3 g have the same number of sig figs?

Yes — both have 3 sig figs

Do 405 K and 405.0 K have the same number of sig figs?

No — 405 K has 3 sig figs, 405.0 K has 4

Write 8537 L in scientific notation with 2 sig figs.

8.5 x 10^3 L

Write 31000 g in scientific notation with 2 sig figs.

3.1 x 10^4 g

Write 160000 m in scientific notation with 2 sig figs.

1.6 x 10^5 m

Write 0.000120 cm in scientific notation with 2 sig figs.

1.2 x 10^-4 cm

Is "31 students in the laboratory" a measured or exact number?

Exact (a count)

Is "1 m = 100 cm" an exact or measured number?

Exact (defined relationship)

Is "my chemistry book weighs 8 lb" a measured or exact number?

Measured

Is "a blood cholesterol level of 184 mg/dL" measured or exact?

Measured

Round 56.855 m to 3 sig figs.

56.9 m

Round 0.002282 g to 3 sig figs.

0.00228 g (2.28 x 10^-3 g)