C12.1 - C12.6 - Chemical Analysis✔️ Flashcards
What is a pure substance?
A substance that is made up of just one substance - that substance can either be an element or compound
What are an elements fixed points?
The melting and boiling points of an element or a compound are called its fixed point
How can fixed points be used to identify pure elements and compounds?
Pure elements and compounds melt and boil at specific temperatures and these fixed points can be used to identify them - meltinga point and boiling point data can be used to distinquish pure substances
What are fomulations?
formulations are useful mixtures made up in definite proportions,designed to give a product the best properties possible to carry out its function
Why is chromatography used?
Used to seperate mixtures and give information to help identify substances - involves a stationary phase and a mobile phase - seperation depends on the distribution of susbstances between the phases
What are Rբ values?
Retention factor value which can be measured and matched against databases to identify substances
Equation for Rբ?
Rբ = distance moved by a substance / distance moved by solvent
What will happen to the compounds in a mixture when they seperate?
Compounds will seperate into different spots depending on the solvent - but pure compounds will produce a single spot in all solvents
What is the test for hydrogen?
Use a burning splint held at the open end of a test tube of the gas - hydrogen burns rapidly with a pop sound
What is the test for oxygen?
Uses a glowing splint inserted into a test tube of the gas - splint relights in oxygen
What is the test for chemical dioxide?
Uses an aqueous solution or calcium hydroxide (lime water) when carbon dioxide is shaken with or bubbled through limewater the limewater turns milky (cloudy)
What is the test for chlorine?
Uses litmus paper - which when damp blue litmus paper is put into chlorine the litmus paper is bleached and turns white
Colour for the lithium ion(Li+) in a flame test?
Crimson
Colour for sodium ion (Na+) in a flame test?
Yellow
Colour for potassium ion (K+) in a flame test?
Lilac
Colour for clacium ion (Ca2+) in a flame test?
Orange- red
Colour for copper ion (Cu2+) in a flame test?
Green
Explain how a flame test is set up?
- nichrom wire loop dipped in concentrated hydrochloric aicd and heated (to clean it)
- dipped in acid again before being dipped into metal compound being tested
- hold loap in roaring flame of bunsern burner
- use colour of flame to identify metal ion in the compound
Why is sodium hydroxide solution used?
Can be used to identify metal ions that form insoluble hydroxides in precipitation reactions
What ions form white precipitates when tested with sodium hydroxide solution?
- aluminium ions
- calcium ions
- magensium ions
What happens if you add more sodium hydroxide to aluminium ions,calcium ions and magensium ions?
The precipitate formed with aluminium ions dissolves however the white precipitate formed with calcium or magnesium ions will not dissolve (so calcium and magnesium can be distinguished by a flame test)
What colour precipitates forms with copper(II) ions?
Blue precipitate
What colour precipitates forms with iron(II) ions?
Green precipitate is produced
What colour precipitates forms with iron(III) ions?
Brown precipitate is formed
How can you test a substance for being a carbonate?
Add dilute acid to a carbonate - it fizzes and produces carbon dioxide gas - the gas turns limewater milky (cloudy)
What happens with carbon dioxide gas in limewater - explain why this happens?
Carbon dioxide reacts with the alkaline, calcium hydroxide - it forms a white precipitate of calcium carbonate which turns the limewater milky (cloudy)
How can you identify halides?
By adding dilute nitric acid and then silver nitrate solution which produces a precipitate of silver halide
Which colour will the precipitates be when identifying halides?
- Chloride - white
- bromide - cream
- iodide - yellow
How can you test for sulfates?
By adding hydrochloric acid (to remove carbonate ions that would form)and then barium chloride solution which produces a white precipitate of barium sulfate (which tells you sulfate ions are present)
Benefits of modern instrumental methods over older?
- they are highly accurate and sensitive
- they are quicker
- they enable small samples ro be analysed
Disadvantages of using instrumental methods are that the equipment …?
- is usually expensive
- takes special training to use
- gives results that can often be interptreted only by comparison with data from known substances
What is flame emission spectroscopy?
An exmaple of an instrumental method which will tell us which metal ions are present from their characteristics line spectra and also the concentration of metal ions in a solution
How are fomulations made?
Made by mixing the components in carefully measured quantities to ensure that the product has the required properties - examples formulations are fuels,medicines and foods
How can Rբ values be used to identify compounds?
Different compounds have different Rբ values in different solvents, which can be used to help identify the compounds
How can chromatography be used to seperate mixtures of substances dissolved in a solvent?
Mixture of substances dissolved in a solvent move up a piece of chromatography paper - the different substances are seperated because of their different solubilities in the solvent used
