Chemical Analysis

• Pure substance

  A substance that contains only one element or compound - not a mixture
• Pure substance examples

  water

  copper sulfate

  glucose

  oxygen gas

  sodium chloride
• Pure substance melting & boiling point

  A chemically pure substance will melt or boil at a specific temperature
• Testing for a pure substance

  By measuring its melting or boiling point and comparing it with the melting or boiling point of the pure substance - find in a data book

  The closer your measured value is to the actual melting or boiling point, the purer the sample is
• Reference substances

  A pure sample that's run next to the tested substance to see if it's a component in the mixture - provide valuable evidence but not proof
• Impurities affect on boiling point

  Impurities will increase the boiling point & may result in the sample boiling at a range of temperatures
• Impurities affect on melting point

  Impurities will lower the melting point & increase the melting range of your substance
• Formulation

  A mixture that has been designed to produce a useful product
• Quantities in a formulation

  Each chemical component must be present in a precisely measured quantity
• Formulation examples (7)

  fuels

  cleaning agents

  paints

  metal alloys

  medicines

  fertilisers

  foods
• Paint formulation substances (4)

  Pigment

  Solvent

  Binder

  Additives
• Pigment in paint

  Pigment - gives the paint colour - white paints have titanium oxide
• Solvent in paint

  Solvent - dissolves the other components & alters viscosity
• Binder in paint

  Binder - forms a film that holds the pigment in place after it's been painted on
• Additives in paint

  Additives - further change the physical & chemical properties of paint
• Chromotography

  A method of separation & analysis of a mixture of soluble chemical substances
• Chromatogram in chromatography

  end product
• Base line in chromatography

  pencil line
• Stationary phase in chromatography

  chromatography paper
• Solvent font in chromatography

  height reached by solvent
• Mobile phase in chromatography

  solvent
• Chromatography phases states

  Stationary - solid or viscous liquid

  Mobile - liquid or gas
• Chromatography experiment

  1. use a pencil to draw a horizontal line near the bottom of the chromatography paper

  2. place the chromatography paper in a beaker containing a small volume of solvent

  3. let the solvent move to a few cm below the end of the paper

  4. as the solvent rises through the paper it dissolves the sample mixture which will then travel up the paper
• Small and large particles in a chromatography

  Small particles travel further than large particles due to the differences in solubility & their attractions with the paper
• Where is the solvent in a chromatography?

  Solvent is below the base line so it doesn't run up the paper
• Chromatography explanation

  The substances in the sample constantly move between the mobile & stationary phases - an equilibrium is formed between the 2 phases

  The mobile phase moves through the stationary phase and anything dissolved in the mobile moves with it.

  How quickly a chemical moves depends on how it's distributed between the 2 phases

  More time in the mobile than stationary = moves further through the stationary
• Pure substances in a chromatography

  Only ever form one spot in any solvent as there is only one substance in the sample
• Time molecules spend in each phase depends on

  How soluble they are in the solvent & how attracted they are to the paper

  Higher solubility & low attraction = more time in the mobile phase
• Rf value

  Distance travelled by substance / distance travelled by solvent

  
• Test for chlorine gas

  Chlorine bleaches damp litmus paper, turning it from red to white
• Test for oxygen gas

  Relights a glowing splint
• Test for carbon dioxide gas

  Bubble through limewater & it turns cloudy
• Test for hydrogen gas

  Lit splint - squeaky pop
• Why is there a 'squeaky pop' when a lighted splint is placed into hydrogen?

  This noise is generated because hydrogen burns rapidly in the presence of oxygen to give H2O
• Test for carbonates

  -add dilute acid

  -bubbles of CO2 gas produced through limewater

  -should turn limewater cloudy

  
• Test for halides

  1. Add dilute nitric acid

  2. add silver nitrate solution

  3. produces a precipitate of silver halide
• Chlorine precipitate colour

  white
• Bromine precipitate colour

  cream
• Iodide precipitate colour

  yellow
• Why do you add dilute nitric acid when testing for halides?

  Removes carbonate ions - these could disrupt test results by forming a precipitate with the silver ions