Quantitative Analysis

Portfolio Activity! This counts toward your final grade!


What are my objectives while studying this topic?


By studying this topic you’ll learn how qualitative analysis helps you measure how much of a chemical you have in a sample.


Why is this important?


Quantitative analysis is useful for trying to find out how much waste is being produced by a factory, for example. It can also be used by scientists who are checking on the quality of their products or by hospitals who are trying to find out how much of a chemical is in somebody’s body.


Who uses these techniques?


So, who uses all these analytical techniques you've been studying? There are many companies that use Analytical Science. Some companies make chemicals and have to analyse their quality. Other companies, such as hospitals labs, analyse samples obtained from other sources.


In this section, you will research two different companies that use analytical science. You will have to explain what type of work they do, the jobs that their staff carry out and the types of legal constraints that the company has to follow and adhere to.


The quality of your writing is very important here so it would be useful if you could research two very different types of companies. For example, a large and small company or one that is profit making and one that is not.


Can I get an introduction to this topic?


Yes, why not have a look at the following clip:



So, let’s get to it: what is qualitative analysis?


The quantity part of the word means that we’re dealing with amounts: masses and volumes. This type of analysis helps us to measure quantities of substances produced or used in reactions rather than simply noting the nature of the reaction.


What will I be expected to be able to do after studying this topic?


  • Understand how or where quantitative volumetric analysis is used

  • Prepare standard solutions for titration using a standard procedure

  • Write a comprehensive risk assessment of the titration that is carried out

  • Carry out a titration accurately

  • Given the relevant equations for the reaction, carry out calculations to determine the concentration of the substances in question

  • Analyse and interpret results and evaluate the investigation

What are the key words to learn and use?


  • Titration

  • Volumetric flask

  • Mole

  • Standard solution

  • Titre

  • Concordant

  • End-point


How long will this topic take to study?


On average you’ll be looking at about ten hours of study time.


What are the main activities on this topic?


Activity


Depending on how much work you’ve done at GCSE, you may have to learn how to work out the relative molecular masses of compounds using the relative atomic masses of the atoms in them (this is the mass number of the atom found on the Periodic Table). You can learn how to do this on the following website - if you already know how to do it, there are some examples for you to have a go with.



When you’ve done this, you’ll need to learn about the MOLE. In Science, this is not the small grey animal that’s a nuisance in your garden, but a UNIT OF MEASUREMENT. A mole of a substance is simply the mass in grams of its relative molecular mass:

For example, the relative molecular mass of water, H2O is 18, so 1 mole of water weighs 18g.


The following equation is very important when we’re doing quantitative analysis:


Number of moles of a substance = mass in g of the substance


Its Relative Atomic or Molecular mass


So, if you know how much of a substance you’ve got in grams and you know its atomic or molecular mass, you can find out how many moles of it you’ve got. As long as you know two out of three things from the above equation, you can work out the third. Look at the triangle below - you’ve probably used them before in Physics or in Maths:


Triangle

If you want to know how many grams of a substance you’ve got and you know how many moles and its atomic or molecular mass, you can multiply them together and get the answer.


For help with this, you can go to the following website:



You can use this equation in the following experiment:


Experiments!


Using the mole equation, go on to make solutions and work out their concentration in mol/dm3.



When you’re happy you understand what you’ve just done, you can go on to the main experiments in this unit. These are:


Preparing a standard solution and carrying out a titration.

You need to research what a standard solution and titration are.


You will be given the opportunity to make a standard solution and carry out a titration in class.


A titration involves an ‘indicator’, which changes colour depending on the conditions within the reaction. You will remember that Universal Indicator changes colour depending on the pH - Universal Indicator is not usually used in titrations because it’s hard to get an exact colour change for a particular pH. You can see from the following diagram that different indicators are different colours in different pHs. One that you will commonly use is phenolphthalein - what are the colour changes you expect with this indicator? What about Methyl orange - another common indicator?


What does this tell you?

 

When you’re comfortable with the procedures for making a standard solution and carrying out a titration, you will be given an investigation to carry out that uses these techniques.


You may be asked to work out how much calcium carbonate is in egg shells by reacting them with hydrochloric acid. Or you may be asked to find out how much salt is in butter. You can find out about this second investigation by going to the following website:



Portfolio Activity


Write your experiments up for submission using the following writing frame:



You should include definitions of standard solution and titration, the standard procedures used for carrying these out and all of the results you obtained during your investigation. You should also try and include the following:


  • Research on applications of volumetric analysis

  • Risk Assessment

  • Tables of Results

  • Calculations

  • Interpretation & Conclusions


Part of your assessment requires you to use other people’s work, such as adapting standard procedures or finding out and using information on the internet. When you use information like this you need to reference it properly in your reports. The following link takes you to a suitable method for referencing:



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