chemical analysis topic 8

whats a pure substance, when does it melt/boil, how can you test for purity, what do impurities do….

whats a pure substance, when does it melt/boil, how can you test for purity, what do impurities do….

• pure substance → something that only contains 1 compound/ element throughout - not mixed w anything else

• will melt/ boil at a specific temp

• can test purity of sample by measuring its melting/boiling point & comparing it w the mp/bp of pure substances (find from data book), the closer measured value is to actual mp/bp the purer ur sample is

• impurities in sample will lower mp & increase melting range of your substance, and will also increase bp & may result in sample boiling at range of temps

whats formulation, pigment, solvent, binder, additives

• formulations → useful mixtures w precise purpose that r made by following ‘formula’. Each component in a formulation is present in a measures quantity & contributes to properties of formulation so that it meets its required function

• pigment → gives paint colour

• solvent → used to dissolve the other compounds & alter viscosity

• binder (resin) → forms film that holds pigment in place after its been painted on

• additives → added to further change physical & chemical properties of the paint

what r formulations important & example, where r they found in everyday life, when u buy a product… & example

• formulations r really important to pharmaceutical industry. For example, by altering formulation of a pill, chemists can make sure it delivers drug to correct part of the body at right concentration, that its consumable & have a long shelf life

• in everyday life, formulations can be found in cleaning products, fuels, cosmetics, fertilisers, metal alloys & even food & drink

• when buy product u might find it has info about its composition on packaging. For example, ratio/ percentage of each component, this tells u a products formulation & also lets u choose formulation w right composition for ur particular use

whats chromatography, mobile phase, stationary phase

• chromatography → is an analytical method used to separate substances in a mixture. Can then use it to identify substances

• mobile phase → where molecules can move. Always liquid/ gas

• stationary phase → where molecules cant move. Can be solid/ really thick liquid

during chromatography the substances in sample…., mobile phase moves through the…,

chemicals that spend more time in mobile phase, components mixture will normally separate…

1. during chromatography experiment, the substances in sample constantly move between the mobile & stationary phase - an equilibrium is formed between the 2 phases

2. mobile phase moves through the stationary phase & anything dissolved in mobile phase moves w it. How quickly chemical moves depends on how its ‘distributed‘ between 2 phases - whether it spends more time in mobile phase/ stationary phase

3. chemicals that spend more time in mobile phase than stationary phase will move further

4. components in a mixture will normally separate through the stationary phase so long as all components spend diff amounts of time in mobile phase. No. of spots may change in diff solvents as the distribution of chemical will change depending on solvent. A pure substances will only every form 1 spot in any solvent as there is only 1 substance in sample

whats a chromatogram, R_f equation, y is chromatography often carried out, R_f value is dependant on solvent…

• result of chromatography analysis is called chromatogram

• R_f= distance travelled by substance (B) / distance travelled by solvent (A)

• chromatography is often carried out to see if certain substance is present in a mixture. To do this, u run a pure sample of that substance (a reference) alongside the unknown mixture. If R_f values of reference & one of spots in mixture match, the substance may be present (although u haven’t yet proved they’re same)

• R_f value is dependant on solvent - if change solvent the R_f values for substance will change. Can test both mixture & reference in no. if diff solvents. If R_f value of reference compound matches R_f value of one of spots in mixture in all the solvents then its likely the reference compound is present in mixture. If spots in mixture & spot in reference only have same R_f value in some solvents then the reference compound isnt present in mixture

What r the 4 tests for gases

1. Chlorine → chlorine bleaches damp litmus paper, turning it white (may turn red for moment first though - because a solution of chlorine is acidic)

2. oxygen → if put glowing splint inside test tube containing oxygen, the oxygen will relight the glowing splint

3. carbon dioxide → bubbling carbon dioxide through (or shaking carbon dioxide with) an aqueous solution of calcium hydroxide (limewater) causes the solution to turn cloudy

4. hydrogen → if hold a splint at open end of test tube containing hydrogen, you’ll get squeaky pop (noise comes from hydrogen burning quickly w oxygen in air to form H_2O)

whats the test for dilute acid which can help detect carbonates

• carbonates r substances that contain CO_3²- ions. Can test whether mystery solution contains carbonate ions by putting sample in test tube & then using dropping pipette to add couple of drops of dilute acid. Should then connect test tube to a test tube of limewater. If carbonate ions r present, carbon dioxide will be released that will turn limewater cloudy when it bubbles through it

whats the test for sulfates w HCL & barium chloride

• to identify sulfate ions (SO_4²-), use a dropping pipette to add couple drops of dilute hydrochloric acid (HCL) following bu couple drops of barium chloride solution (BaCl_2) to test tube containing ur mystery solution. If sulfate ions r present a white precipitate of barium sulfate will form

what the test for halides (Cl^-, Br^-, I^-) w nitric acid & silver nitrate, what r the 3 precipitates that could form & from what

• to identify a halide ion, add couple drops of dilute nitric acid (HNO_3), followed by couple drops of silver nitrate solution (AgNO_3) to solution

compounds of some metals…, can test for various metal ions by… & give 5, to do the test…, u can use these colours to…, (flame test)

….

some metals r insoluble &…, in this test add…, what r the 6 metal ions & colour of precipitate & ionic equation for precipitate formation

….

during flame emission spectroscopy…, what does it pass through & what does that do, combination of wavelengths emitted by ion depends…, intensity of spectrum indicates…, this means…

• during flame emission spectroscopy a sample is placed in a flame. As ions heat up their electrons become excited. When the electrons drop back to their og energy levels they transfer energy as light

• the light passes through a spectroscope which can detect diff wavelengths of light to produce a line spectrum

• combination of wavelengths emitted by a ion depends on its charge & its electron arrangement. Since no 2 ions have the same charge & same electron arrangement, diff ions emit diff wavelengths of light. So each ion produces a diff pattern of wavelengths & has diff line spectrum

• intensity of spectrum indicates the concentration of that ion in solution

• means that line spectrums can be used to identify ions in solution & calculate their concentrations

flame emission spectroscopy can also be used to…. & this means..

• flame emission spectroscopy can also be used to identify diff ions in mixtures. This makes it more useful than flame tests, which only work for substances that contain a single metal ion

chemists often use…, 3 advantages of using machines

• chemists often use instrumental analysis (test that uses machines) such as flame emission spectroscopy instead of conducting tests

• advantages of using machines:

  • very sensitive - can detect even the tiniest amounts of substances

  • very fast & tests can be automated

  • very accurate