Unit 0 Review

Which of the following is NOT a standard safety rule in the laboratory?

• Always wear safety goggles when working with chemicals

• Never leave a lit Bunsen burner unattended

• You can dispose of chemicals in the sink as long as they are liquid

• Always wash your hands after handling chemicals

Answer explanation

Disposing of chemicals in the sink is unsafe and against standard laboratory rules, as it can cause contamination and environmental hazards. The other options are essential safety practices.

How many significant figures are in the number 0.004520?

• 4

• 3

• 5

• 2

Answer explanation

The number 0.004520 has 4 significant figures. The leading zeros are not counted, but the digits 4, 5, 2, and the trailing zero after 2 are significant.

What is the result of the following addition, reported to the correct number of significant figures: 12.11 + 3.7

• 15.81

• 15.8

• 16

• 15.7

Answer explanation

To add 12.11 and 3.7, align the decimal points: 12.11 + 3.70 = 15.81. The result should be reported with the least number of decimal places, which is one (from 3.7). Thus, the answer is 15.8.

What is the correct result when multiplying 5.12 and 3.004, rounded to the correct number of significant figures?

• 15.37

• 15.36

• 15.4

• 15.3

Answer explanation

To multiply 5.12 (3 significant figures) and 3.004 (4 significant figures), the result is 15.36608. Rounding to 3 significant figures (the lesser count) gives 15.4, making it the correct answer.

Why is it important to report your final answer in a calculation with the correct number of significant figures?

• To match the precision of your measuring instrument

• To make your calculations look more accurate

• To avoid rounding errors

• To make your answers easier to understand

Answer explanation

Reporting your final answer with the correct number of significant figures is crucial to match the precision of your measuring instrument. This ensures that the accuracy of your calculations reflects the limitations of your measurements.

Round the following number to 2 significant figures: 0.003642

• 0.0036

• 0.0037

• 0.00364

• 0.0040

Answer explanation

To round 0.003642 to 2 significant figures, we focus on the first two non-zero digits, which are '3' and '6'. The next digit is '4', which does not round up. Thus, the answer is 0.0036.

How many significant figures are in the number 4.500 x 10²?

• 3

• 4

• 2

• 5

Answer explanation

The number 4.500 x 10² has four significant figures. The digits 4, 5, 0, and 0 are all significant because the trailing zeros in a decimal number indicate precision.

A student is determining the density of a liquid. They find the mass to be 12.45 g and the volume to be 4.1 cm³. What is the density, rounded to the correct number of significant figures?

• 3.0 g/cm³

• 3.04 g/cm³

• 3.037 g/cm³

• 3.0366 g/cm³

Answer explanation

To find density, use the formula density = mass/volume. Here, density = 12.45 g / 4.1 cm³ = 3.03658... g/cm³. Rounding to two significant figures (based on the volume's 2 significant figures) gives 3.0 g/cm³, the correct answer.

What is the correct sum of the following numbers, rounded to the correct number of decimal places? 15.678 + 4.2 + 3.45

• 23.3

• 23.4

• 23.33

• 23.32

Answer explanation

To find the sum, add the numbers: 15.678 + 4.2 + 3.45 = 23.328. Rounding to one decimal place gives 23.3, but rounding to two decimal places gives 23.33. The correct answer, rounded to one decimal place, is 23.3.

How many significant figures are in the following measurement: 0.00560 g?

• 3

• 2

• 4

• 5

Answer explanation

The measurement 0.00560 g has three significant figures: the '5' and '6' are significant, and the trailing '0' is significant because it follows a decimal point. The leading zeros are not counted.