Module 0 (Things You Should Already Know): Units, Sig Figs, Lab Glassware

What does Numerical Uncertainty mean? What is the first uncertain value of a number?

Measurements and measuring tools are inexact.

The first uncertain value of a number is its last significant figure.

Describe Glassware and Accuracy.

What are some types of glassware used in the lab?

Manufacturers sometimes indicate accuracy on glassware.

Some glassware we will use in labs include beakers, Erlenmeyer flasks, graduated cylinders, volumetric pipettes, and volumetric flasks.

Beakers and Erlenmeyer Flasks

What is their uncertainty and what are they used for?

Beakers and Erlenmeyer flasks usually have a tolerance of ±5% of the total volume. These are usually used for gross/rough measurements.

Volumetric Pipettes and Volumetric Flasks

What is their uncertainty and what are they used for?

Volumetric pipettes and flasks have no incremented lines, so round based on the printed error.

For example, ±0.012 mL has uncertainty beginning at the hundredth place so round your measurements to the hundredths place.

Graduated Cylinders

What is their uncertainty and what are they used for?

Graduated cylinders have incremented lines that you can use to estimate volume. Round using the 10% rule and measure from the bottom of the meniscus.

What is the 10% Rule?

estimate the value up to 10% of the smallest line

For example, a glass burette is graduated in 0.1 mL increments, so values should be taken to the nearest x.x1 mL.

What is Standard Deviation?

How is it determined?

the measurement of statistical experimental uncertainty, based on the formula

In EXCEL you can find standard deviation using the functions STDEV or LINEST

How do you round the mean and standard deviation using the proper number of sig figs?

Round standard deviation to the first number, unless the first number is 1 (ones rule) in which case round to the first two numbers

The mean should also be rounded to the same decimal place as the standard deviation because it cannot be more accurate than the standard deviation.

Describe the rules for Sig Figs for different types of calculations.

Addition and Subtraction: round to the leftmost decimal place

Multiplication and Division: round to the smallest number of sig figs

Logarithms: round the mantissa to the same number of sig figs in the log

Exponents: round the result to the same number of sig figs in the exponent’s mantissa