Basic Chemistry

What is chemistry?

The study of matter and how its behavior relates to its particles.

What is matter?

Anything that has mass and takes up space.

What is an atom?

A tiny building block of ordinary matter.

What is a molecule?

Two or more atoms bonded together.

What is the central idea of atomic theory?

Ordinary matter is made of atoms.

Why do particle arrangements matter?

Different arrangements and interactions can produce different properties.

Are chemicals found only in laboratories?

No. Ordinary materials such as water and air contain chemicals.

What is the scientific method?

Learning through observations, testable explanations, experiments, and revision based on evidence.

What is an observation?

Something noticed or measured.

What is a hypothesis?

A proposed, testable explanation of observations.

What is an experiment?

A controlled test of an explanation.

What does falsifiable mean?

Evidence could show the explanation is wrong.

What is a scientific law?

A statement describing a consistent pattern in observations.

What is a scientific theory?

A supported explanation of observations and patterns.

Does a theory eventually become a law?

No. Theories explain; laws describe patterns.

Why isn’t “it has been tested many times” enough to distinguish a law from a theory?

Both laws and theories can have extensive experimental support.

What should scientists do when reliable evidence contradicts an explanation?

Reconsider, revise, or replace it, then test again.

What is the law of conservation of mass?

Total mass is conserved in an ordinary chemical reaction when all material is accounted for.

Can a reaction form new substances without creating new atoms?

Yes. Existing atoms rearrange into new combinations.

What does combustion mean?

Burning

Why is weighing only ash an incomplete test of mass conservation?

It excludes gaseous products and doesn’t account for oxygen that reacted.

Why did closed containers help Lavoisier study mass conservation?

They kept material from escaping or entering.

What was phlogiston?

A proposed substance once thought to escape during burning.

What evidence challenged the original phlogiston explanation?

Metals gained mass when burned, although the explanation predicted a loss.

Why can a metal gain mass when it burns?

Oxygen from the air combines with it.

What was a calx?

The historical name used here for a metal oxide.

What are data?

Collected observations or measurements.

What is quantification?

Expressing observations using numbers and measurements.

What is a ratio?

A comparison of amounts using division.

What does water’s approximate 8:1 oxygen-to-hydrogen ratio describe?

Mass, not numbers of atoms.

What should you check before interpreting a graph?

Axis labels, units, scales, and the trend or slope.

What does a graph’s slope describe?

How quickly one variable changes relative to another.

What does an upward line becoming steeper mean?

The amount is increasing faster and faster.

Does changing the graph’s scale change its data?

No. It changes how the data appear.

What three habits does Section 1.5 emphasize?

Curiosity, willingness to calculate, and commitment to learning.

What gas makes soda fizz?

Carbon dioxide.

Does a drop of soda contain thousands, millions, trillions, or vastly more atoms?

Vastly more than one trillion atoms. Atoms are extraordinarily small.

Why is chemistry called a central science?

It connects many sciences through the study of matter and its interactions.

Basic versus applied research?

Basic builds understanding; applied addresses a practical problem.

What does a control condition provide?

A baseline for comparison.

Why did Redi use gauze?

It allowed air in while keeping flies away from the meat.

Can scientific theories make predictions?

Yes. Theories explain and can predict; laws describe consistent patterns.

What two parts make up a measurement?

A number and a unit.

What is a unit?

An agreed-upon standard used to measure a quantity.

Why must you check units?

The same number with different units can represent different amounts.

What mistake does the Mars Climate Orbiter example illustrate?

Treating different unit systems as interchangeable.

What is the standard form of scientific notation?

a * 10^n, where 1<a<10 for positive numbers.

What is the coefficient?

The number multiplying the power of ten.

When converting into scientific notation, moving the decimal left gives what exponent sign?

Positive

When converting into scientific notation, moving the decimal right gives what exponent sign?

Negative

What determines the exponent’s magnitude?

The number of decimal places moved.

Does a negative exponent mean a negative value?

No. It means division by a power of ten.

Convert 62,000 into scientific notation.

6.2*10^4

Convert 0.00062 into scientific notation.

6.2*10^{-4}

Convert 4.7*10^{-3} into ordinary notation.

0.0047

Convert 4.7*10^3 into ordinary notation.

4700

What do significant figures communicate?

The precision reported in a measurement.

Which reported digit is uncertain?

The last digit.

A ruler has marks every 1 mm. What place do you estimate to?

0.1 mm, one place finer.

A pointer balance has marks every 0.1 g. What place do you estimate to?

0.01 g.

How do you record a digital balance reading?

Use the displayed digits, including displayed ending zeros. Don’t add an invented digit.

Why isn’t 1.3 g equivalent to 1.30 g in reported precision?

1.30 g reports finer detail, although their numerical values are equal.

Do nonzero digits count?

Yes.

Do zeros between nonzero digits count?

Yes.

Do leading zeros count?

No. They position the decimal.

Do ending zeros count when a decimal point is written?

Yes.

How many significant figures are in measured 500, using your instructor’s rule?

1.

How many significant figures are in 0.00620?

3: 6, 2, and the final 0.

How many significant figures are in measured 4,050?

3: 4, the interior 0, and 5.

How many significant figures are in 4,050.0?

5.

How many significant figures are in 6.200*10^{-3}?

4. Count the coefficient’s digits.

Are significant figures the same as decimal places?

No. Significant figures exclude leading placeholder zeros.

What should you ask before counting significant figures?

Is this number exact or measured?

How many significant figures does an exact number have?

Unlimited.

What three sources can produce exact numbers?

Exact counts, defined quantities, and exact mathematical factors.

You count exactly 20 flowerpots. How many significant figures?

Unlimited—it is an exact count.

A scale measures 20 g. How many significant figures under your instructor’s rule?

1—it is a measurement without a written decimal point.

Is 100 cm = 1 m exact?

Yes. It is a defined relationship.

Is every conversion factor exact?

No. Some are based on measurements.

Is the 2 in radius = diameter ÷ 2 exact?

Yes. It comes from the mathematical relationship.

Accuracy versus precision?

Accuracy = close to the reference value. Precision = repeated measurements close together.

Can measurements be precise but inaccurate?

Yes. They can cluster together away from the reference value.

Why do we round answers calculated from measurements?

To report only the precision justified by the measurements.

What is a decimal place?

A digit’s position to the right of the decimal point.

How many decimal places does 12.45 have?

Two: the 4 and 5.

How many decimal places and significant figures does 0.0060 have?

Four decimal places and two significant figures.

What rule applies to multiplication and division?

Report the same number of significant figures as the measured quantity with the fewest significant figures.

What rule applies to addition and subtraction?

Round to the least precise place value—usually the fewest decimal places.

Does the smallest numerical value always determine rounding?

No. Compare significant figures or place-value precision, depending on the operation.

Which digit determines whether to round up?

The first digit being dropped.

What happens when the first dropped digit is 0–4?

Leave the last kept digit unchanged.

What happens when the first dropped digit is 5–9?

Increase the last kept digit by one.

Round 2.449 to two significant figures. Why?

2.4. The first dropped digit is 4; the later 9 does not change the decision.

Round 623 to two significant figures.

620, clearly written as \(6.2\times10^2\).

Why does rounding 623 to two significant figures give 620 rather than 62?

The zero preserves the hundreds-and-tens place values and the number’s approximate size.

Round 687 to two significant figures.

690, clearly written as \(6.9\times10^2\).

Report \(4.2\times1.36=5.712\) correctly.

5.7: multiplication is limited to two significant figures.

Report 12.45 + 3.2 = 15.65 correctly.

15.7: addition is limited to one decimal place.

If an answer needs three significant figures and the calculator shows 6, how should you write it?

6.00. The zeros communicate the required precision.

Do exact counts and defined conversion factors limit significant figures?

No. They have unlimited significant figures.