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Give the number of significant figures in each of the following numbers: (a) \(0.0123 \mathrm{g}\) (b) \(3.40 \times 10^{3} \mathrm{mL}\) (c) \(1.6402 \mathrm{g}\) (d) \(1.020 \mathrm{L}\)

Short Answer

Expert verified
(a) 3, (b) 3, (c) 5, (d) 4.

Step by step solution

01

Identify Significant Figures in a Small Decimal

For the number \(0.0123\, \mathrm{g}\), significant figures include all non-zero digits and any zeros between them. Trailing zeros to the right of a decimal point in a number less than one are not significant unless they are between significant figures. The number \(0.0123\) has three non-zero digits: 1, 2, and 3. Thus, it has **3 significant figures**.
02

Determine Significant Figures in Scientific Notation

The number \(3.40 \times 10^{3} \mathrm{mL}\) is in scientific notation. The significant figures are determined by the coefficient \(3.40\). This coefficient has three significant figures: 3, 4, and the trailing zero after the decimal point. Hence, there are **3 significant figures**.
03

Count Significant Figures in a Whole Number with Trailing Zero

For the number \(1.6402\, \mathrm{g}\), every digit is significant, including the zero, since it is between non-zero digits. There are four non-zero digits and one zero: 1, 6, 4, 0, and 2. Therefore, it contains **5 significant figures**.
04

Evaluate Significant Figures in a Number with Trailing Zero

The number \(1.020\, \mathrm{L}\) includes all non-zero digits and any trailing zeros after the decimal point since they indicate precision. Thus, the digits 1, 0, 2, and the trailing zero are significant, giving a total of **4 significant figures**.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Scientific Notation
Scientific notation is a way to express very large or very small numbers in a more compact form. It's crucial for handling numbers in scientific work. The number is typically expressed in the form \( a \times 10^n \), where \( a \) is a number greater than or equal to 1 and less than 10, and \( n \) is an integer. This makes it easier to read, write, and convey the precision of a number.

For example, the number \(3.40 \times 10^{3} \mathrm{mL}\) has a coefficient of \(3.40\). The coefficient in scientific notation dictates the number of significant figures, which in this case are three: 3, 4, and the trailing zero. This representation indicates that the precision of the measurement includes the thousandths place. Keep in mind that when dealing with scientific notation, only the digits in the coefficient are counted as significant figures.
Decimal Places
Decimal places refer to the number of digits to the right of the decimal point in a number. They are important for representing the precision of measurements and computations. The more decimal places you include, the more precise your number can be said to be.

Consider the number \(1.020\, \mathrm{L}\). It has three decimal places: 0, 2, and 0. Each of these decimal digits plays a significant role, because they help show the exactness of the measurement. By including digits beyond the whole number, one can convey a finer precision in scientific work. Decimal numbers such as these must be accurately reported to ensure clarity in communication of data.
Trailing Zeros
Trailing zeros are zeros that appear to the right of the last non-zero digit in a number. Their significance can change based on the presence of a decimal point. In numbers with a decimal point, such as \(1.020\, \mathrm{L}\), trailing zeros are significant because they reflect the precision of the measurement.

Without a decimal point, trailing zeros are generally not considered significant. For example, in a number like 3000, without additional context such as a decimal point, we cannot assume these zeros are significant. Trailing zeros after a decimal point, like those in \(3.40\), are significant and indicate a reliability of the precision up to that point.
Precision in Measurements
Precision in measurements refers to how closely multiple measurements of the same quantity are to each other. It also indicates how finely a measurement is made. Using significant figures as a tool, precision is shown through the number of meaningful digits in a measured or calculated quantity.

For instance, the number \(1.6402 \, \mathrm{g}\) with five significant figures shows high precision, as it includes detailed information down to a smaller scale. By ensuring each digit contributes valuable information, scientists can communicate data that reflects careful measurement and analysis. Precision is vital for both experimental accuracy and the ability to replicate results in scientific studies.

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Most popular questions from this chapter

The fluoridation of city water supplies has been practiced in the United States for several decades. It is done by continuously adding sodium fluoride to water as it comes from a reservoir. Assume you live in a medium-sized city of 150,000 people and that \(660 \mathrm{L}(170 \mathrm{gal})\) of water is consumed per person per day. What mass of sodium fluoride (in kilograms) must be added to the water supply each year (365 days) to have the required fluoride concentration of 1 ppm (part per million)-that is, 1 kilogram of fluoride per 1 million kilograms of water? (Sodium fluoride is \(45.0 \%\) fluoride, and water has a density of \(1.00 \mathrm{g} / \mathrm{cm}^{3} .\) )

A piece of copper has a mass of \(0.546 \mathrm{g} .\) Show how to set up an expression to find the volume of this piece of copper in units of liters. (Copper density \(=8.96 \mathrm{g} / \mathrm{cm}^{3} .\) )

Suppose your bedroom is \(18 \mathrm{ft}\) long, \(15 \mathrm{ft}\) wide, and the distance from floor to ceiling is \(8 \mathrm{ft}, 6\) in. You need to know the volume of the room in metric units for some scientific calculations. (a) What is the room's volume in cubic meters? In liters? (b) What is the mass of air in the room in kilograms? In pounds? (Assume the density of air is \(1.2 \mathrm{g} / \mathrm{L}\) and that the room is empty of furniture.)

You have an irregularly shaped chunk of an unknown metal. To identify it, you determine its density and then compare this value with known values that you look up in the chemistry library. The mass of the metal is \(74.122 \mathrm{g}\) Because of the irregular shape, you measure the volume by submerging the metal in water in a graduated cylinder. When you do this, the water level in the cylinder rises from \(28.2 \mathrm{mL}\) to \(36.7 \mathrm{mL}\) (a) What is the density of the metal? (Use the correct number of significant figures in your answer.) (b) The unknown is one of the seven metals listed below. Is it possible to identify the metal based on the density you have calculated? Explain. $$\begin{array}{llll} \hline \text { Metal } & \text { Density }\left(\mathrm{g} / \mathrm{cm}^{3}\right) & \text { Metal } & \text { Density }\left(\mathrm{g} / \mathrm{cm}^{3}\right) \\ \hline \text { zinc } & 7.13 & \text { nickel } & 8.90 \\ \text { iron } & 7.87 & \text { copper } & 8.96 \\ \text { cadmium } & 8.65 & \text { silver } & 10.50 \\ \text { cobalt } & 8.90 & & \\ \hline \end{array}$$

Eight observations are listed below. Which of these observations identify chemical properties? (a) Sugar is soluble in water. (b) Water boils at \(100^{\circ} \mathrm{C}\) (c) Ultraviolet light converts \(\mathrm{O}_{3}\) (ozone) to \(\mathrm{O}_{2}\) (oxygen). (d) Ice is less dense than water. (e) Sodium metal reacts violently with water. (f) \(\mathrm{CO}_{2}\) does not support combustion. (g) Chlorine is a yellow gas. (h) Heat is required to melt ice.

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