Unit 8 - Chemical Analysis Flashcards
What is a pure substance
-single element or compound not mixed with any other substance
-pure elements and compounds melt and boil at specific temperatures
-melting and boiling point can be used to distinguish pure substances from mixtures
-you can test purity of substance by measuring it’s be,ting or boiling point, the closer your measured value is to the actual MP/BP the purer your substance
What is a formulation
-mixture that has been designed as a useful product
-many products are complex mixtures in which each chemical has a purpose
-made by mixing components in carefully measured quantities to ensure product has required properties
-examples include fuels, cleaning agents, paints, medicines, alloys, fertilisers and foods
What is the test for hydrogen
-hold a burning splint at the open end of a test tube containing hydrogen
-hydrogen burns rapidly with a squeaky pop sound
Test for oxygen
-glowing splint inserted into test tube of gas
-splint will relight in presence of oxygen
What is the test for carbon dioxide
-uses an aqueous solution of calcium hydroxide (limewater)
-when carbon dioxide is shaken with or bubbled through limewater the limewater turns milky (cloudy)
Test for chlorine
-uses litmus paper
-when damp litmus paper is put into chlorine gas the litmus paper is bleached and turns white
What is chromatography
-can be used to separate mixtures and can give information to help identifying substances
-involves stationary ( chromatography paper) mobile phase (solvent)
-compounds in a mixture may separate into different spots deepening on the solvent but a pure substance will produce just one spot in all solvents
Equation used in chromotography
Rf = distance moved by substance / distance moved by solvent
What do flame tests identify
-Metal ions (cations)
-if a sample contains a mixture of ions is used some flame colours can be masked
What colour flame does lithium compounds produce
Crimson
What colour flame does sodium compounds form
Yellow flame
What colour flame does calcium (Ca^2+) compounds form
Orange - red flame
What colour flame does copper (Cu^2+) compounds form
Green flame
How to test for carbonates
-React with dilute acids to form carbon dioxide gas
-then connect this test tube to test tube containing limewater if present it will go cloudy
How to test for halides (bromide, chloride, iodide) and results
-add couple of drops of dilute nitric acid and silver nitrate solution
-chloride gives a white precipitate of silver chloride
-bromide gives a cream precipitate of silver bromide
-iodide gives a yellow precipitate of silver iodide
How to test for sulfates
-sulfate ions in solution produce a white precipitate with barium chloride solution and dilute hydrochloric acid
How to test for metal hydroxides and what they test for
-sodium hydroxide solution can be used to identify some metal ions
Precipitate and ionic equation for calcium (Ca^2+) hydorixde
-white
Ca^2+ + 2OH- —> Ca(OH)2
Precipitate and ionic equation for copper (II) (Cu^2+)
-blue
Cu^2+ + 2OH- —> Cu(OH)2
Precipitate and ionic equation for iron II (Fe^2+)
-green
Fe^2+ + 2OH- —> Fe(OH)2
Precipitate and ionic equation for iron III (Fe^3+)
-brown
Fe^3+ +3OH - —-> Fe (OH)3
Precipitate and ionic equation for aluminium (Al^3+)
-white at first but then dissolves in excess sodium hydroxide to form a colourless solution
-Al^3+ + 3OH- —> Al(OH)3
Precipitate and ionic equation for magnesium (Mg^2+)
-white
Mg^2+ + 2OH- —>Mg(OH)2
Advantages of instrumental methods (using machines)
-very sensitive = they can detect even the tiniest amounts of substances
-very fast and tests can be automates
-very accurate
What is the flame emission spectroscopy and the process
Example of an instrumental method used to analyse metal ions in solutions
-sample is place into flame
-electrons are excited by flames heat and gain energy
-these electrons transfer this energy as light when they return to their original energy levels
-the output is a line spectrum that can be analysed to identify the metal ions in the solution and measure their concentrations
What colour flame does potassium compounds give
Lilac flame
Why for example does caesium and rubidium have different line spectra
Different arrangements of electrons so emit different wavelengths of light when heated
