4.5b Preparing Solutions of Known Concentrations

The dilution method is used to prepare very dilute solutions because?

It is very difficult to weigh small amounts of solute with great accuracy

Volumetric glassware

Laboratory glassware that has been carefully calibrated to contain very accurate volumes or allow for the measurement of very accurate volumes

Because the amount of solute (in moles) in the measured volume of concentrated solution is equal to?

The amount of solute (in moles) in the diluted solution

Steps to Preparing a Solution

1. Weigh out Salt. 2. Carefully transfer salt sample to volumetric flask 3. Add a small amount of water to volumetric flask and swirl until the sample has dissolved 4. Add additional water to the flask, mixing as each portion is added 5. Carefully add water until the bottom of the meniscus sits on the mark on the neck of the flask 6. Stopper the flask and invert it to mix the contents

A student needs approximately 100 mL of water, but does not care if the actual volume is anywhere between 90 mL and 110 mL. Which pieces of glassware are appropriate to use to measure this volume? Erlenmeyer flask buret graduated cylinder graduated pipet transfer pipet volumetric flask beaker

An erlenmeyer flask and the beaker are appropriate

What are examples of volumetric glassware?

Burets and pipets

In the dilution method, the solution is prepared by?

Diluting a more concentrated existing solution with a known concentration

Dilution Method

Generally used to prepare more dilute solutions

Direct Addition Method

Generally used to prepare solutions with relatively high concentrations of solute

A student needs to deliver 4.5 mL of solution to a flask. Which pieces of glassware are appropriate to use? Erlenmeyer flask buret graduated cylinder graduated pipet transfer pipet volumetric flask beaker

The buret and graduated pipet are appropriate to use in this situation

A student wants to dispense 65 mL of a liquid and wants the dispensed volume to be within 1% of the desired volume. Which type of glassware is appropriate? Erlenmeyer flask buret graduated cylinder graduated pipet transfer pipet volumetric flask beaker

The graduated cylinder, best choice for delivering volumes with a fair, but not high, degree of precision

A student wants to prepare 100 mL of a solution with a very precise concentration. Which type of glassware is appropriate to use for this task? Erlenmeyer flask buret graduated cylinder graduated pipet transfer pipet volumetric flask beaker

The volumetric flask