Why does a temperature measurement of 25 °C have three significant figures, while a temperature measurement of -196 °C only has two significant figures? Explain.

Name: Chemistry: A Molecular Approach
Author: Tro
ISBN: 9780134112831

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Understand the concept of significant figures: Significant figures are the digits in a measurement that are known with certainty plus one estimated digit.

Identify the significant figures in positive temperatures: For 25 °C, the digits '2' and '5' are known with certainty, and there is no decimal point, so both are significant, giving us two significant figures. The absence of a decimal point implies that the zero is not significant.

Identify the significant figures in negative temperatures: For -196 °C, the digits '1', '9', and '6' are known with certainty, and there is no decimal point, so all three are significant, giving us three significant figures.

Consider the role of the negative sign: The negative sign in -196 °C is not a digit and does not affect the count of significant figures.

Conclude the explanation: The difference in significant figures arises from the presence or absence of a decimal point and the certainty of the digits, not from the negative sign.

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Significant Figures

Significant figures are the digits in a number that contribute to its precision. This includes all non-zero digits, any zeros between significant digits, and trailing zeros in the decimal portion. Understanding significant figures is crucial for accurately reporting measurements and calculations in scientific contexts.

Temperature Measurement

Temperature is a measure of the average kinetic energy of particles in a substance, commonly expressed in degrees Celsius (°C). The way temperature is measured can affect the number of significant figures reported, as it depends on the precision of the measuring instrument and the context of the measurement.

Rounding Rules

Rounding rules dictate how to express numbers with a specific number of significant figures. When a measurement is taken, if the last digit is less than 5, it is rounded down, while if it is 5 or greater, it is rounded up. This affects how many significant figures are reported, particularly in cases where the measurement is close to a boundary value.