AQA A Level Chemistry复习笔记4.1.1 Making a Volumetric Solution

Making a Volumetric Solution

 

REQUIRED PRACTICAL 1

Volumetric Analysis

  • Volumetric analysis is a process that uses the volume and concentration of one chemical reactant (a volumetric solution) to determine the concentration of another unknown solution
  • The technique most commonly used is a titration
  • The volumes are measured using two precise pieces of equipment, a volumetric or graduated pipette and a burette
  • Before the titration can be done, the standard solution must be prepared
  • Specific apparatus must be used both when preparing the standard solution and when completing the titration, to ensure that volumes are measured precisely

Volumetric-analysis-apparatus

Some key pieces of apparatus used to prepare a volumetric solution and perform a simple titration

 

  1. Beaker
  2. Burette
  3. Volumetric Pipette
  4. Conical Flask
  5. Volumetric Flask

Making a Volumetric Solution

  • Chemists routinely prepare solutions needed for analysis, whose concentrations are known precisely
  • These solutions are termed volumetric solutions or standard solutions
  • They are made as accurately and precisely as possible using three decimal place balances and volumetric flasks to reduce the impact of measurement uncertainties
  • The steps are:

1.2.7-Preparing-a-standard-solution-11.2.7-Preparing-a-standard-solution-2_1

 

Volumes & concentrations of solutions

  • The concentration of a solution is the amount of solute dissolved in a solvent to make 1 dm3 of  solution
    • The solute is the substance that dissolves in a solvent to form a solution
    • The solvent is often water

     

  • A concentrated solution is a solution that has a high concentration of solute
  • A dilute solution is a solution with a low concentration of solute
  • Concentration is usually expressed in one of three ways:
    • moles per unit volume
    • mass per unit volume
    • parts per million

     

Worked Example

Calculate the mass of sodium hydroxide, NaOH, required to prepare 250 cm3 of a 0.200 mol dm-3 solution

Answer:

Step 1: Find the number of moles of NaOH needed from the concentration and volume:

number of moles  = concentration (mol dm-3) x volume (dm3)

n = 0.200 mol dm-3 x 0.250 dm3

n = 0.0500 mol

Step 2: Find the molar mass of NaOH

M = 22.99 + 16.00 + 1.01 = 40.00 g mol-1

Step 3: Calculate the mass required

mass = moles x molar mass

mass =  0.0500 mol x 40.00 g mol-1   = 2.00 g

 

 

转载自savemyexams

更多Alevel课程
翰林国际教育资讯二维码