chemical analysis

• to refer to a substance being pure it means nothing has been added to it and its at it natural state in chemistry this means a substance that only contains one compound or element throughout
• the boiling point and melting point of a substance tells you how pure it is
• to test if a sample substance is pure you can measure its melting and boiling points and compare theses results to the melting and boiling points of pure substances which are recorded on a data book
• impurities in your sample will :

  
  

  • decrease melting point
  • increase boiling point
• impure substances boil and melt over a range of temperatures
• formulations are useful mixtures made with a specific formula to match a specific purpose
• formulations use precise amounts of compounds and have a particular function
• by altering the formulation of a pill you can make sure it goes to the right part of the body at the right concerntration and that the pill is consumable and has a long shelf life
• when you buy a product like paint of cleaning agents the composition and formular of the product is on the packaging
• paper chromotography is a method used to seperate substances from a mixture so you can identify each substance
• chromotography to seperate dyes in an ink: part 1

  • take a piece of filter paper and draw a line near the bottom in pencil this is called the base line and add a sample of ink on the baseline
  • get a beaker and fill it abit with a solven like water and ethenol and put filter paper in making sure baseline and ink sample are just above it
  • put lid on beaker to stop solvent evaporating
• chromotography of seperating dyes in a ink: part 2

  • wait for solvent to seep up paper and each different dye will travel up the paper at different rates
  • once solvent has reached the top of the paper take filter paper out and leave it to dry
• once you take filter paper out of beaker and leave it to dry you get a pattern of spots going up this is called a chromatogram
• to explain why chemicals move up the filter paper at different rates we use the terms:

  • mobile phase - the molecules can move and are usually gas and liquid
  • stationary phase - the molecules cant move and are ususally solids and thick liquids
• in chromotography the solvent is the mobile phase as its a liquid and its molecules move up the filter paper
• in chromotography the filter paper is the stationary phase as its a solid and its molecules dont move
• we use a chromatogram to measure the Rf value of each chemical
• Rf = distance travelled by substance(ink)

  distance travelled by solvent(how far the solvent whent on the paper)
• testing for chlorine will turn damp litmus paper white
• testing for oxygen will re light a glowing splint
• testing for hydrogen will make a glowing splintb in a test tube of hydrogen create a squeaky pop
• testing for carbon dioxide will turn calcium hydroxide cloudy
• to test if a solution contains carbonate ions put a sample of it in a test tube and add dilute acid to it (HCL) and then connect this test tube to some calcium hydroxide if carbonate ions are present carbon dioxide is released and turns the calcium hydroxide cloudy
• anions are negatively charged ions
• cations are positively charged ions