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Chemical Analysis
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- 1What is a pure substance?Something that only contains one compound or element throughout.
- 2Pure Substance: Boiling/Melting PointA chemically pure substance will melt or boil at a specific temperature.
- 3How can you test the purity of a sample?By measuring its melting or boiling point and comparing it with the melting or boiling point of the pure substance (which you can find from a data book).
- 4The closer the measured boiling/melting point of the sample tested is to the actual melting/boiling point, ____?The purer your sample is.
- 5What will impurities in your sample do to the melting point of the substance?Lower the melting point and increase the melting range of your substance.
- 6What will impurities in your sample do to the boiling point of the substance?Increase the boiling point and may result in your sample boiling at a range of temperatures.
- 7What are formulations?Useful mixtures with a precise purpose that are made by following a 'formula'. Each component in a formulation is present in a measured quantity, and contributes to the properties of the formulation so that it meets its required function.
- 8An Example of Formulations: PaintPaints are formulations composed of:
Pigment - gives the paint colour, for example titanium oxide is used as a pigment in white paints.
Solvent - used to dissolve the other components and alter the viscosity.
Binder (resin) - forms a film that holds the pigment in place after it's been painted on.
Additives - added to further change the physical and chemical properties of the paint.
Depending on the purpose of the paint, the chemicals used and their amounts will be changed so the paint produced is right for the job. - 9Why are Formulations Important in the Pharmaceutical Industry?For example, by altering the formulation of a pill, chemists can make sure it delivers the drug to the correct part of the body at the right concentration, that it's consumable and has a long enough shelf life.
- 10Give some examples of where formulations can be found in everyday life?In cleaning products, fuels, cosmetics, fertilisers, metal alloys and even food and drink.
- 11What is Chromatography?An analytical method used to separate the substances in a mixture. You can then use it to identify the substances.
- 12What are the 2 Phases in Chromatography?A mobile phase - where the molecules can move. This is always a liquid or a gas.
A stationary phase - where the molecules can't move. This can be a solid or a really thick liquid. - 13During a chromatography experiment, what happens to the substances in the sample?They constantly move between the mobile and the stationary phases - an equilibrium is formed between the two phases. The mobile phase moves through the stationary phase, and anything dissolved in the mobile phase moves with it.
- 14How quickly a chemical moves depends on what?How it's 'distributed' between the two phases - whether it spends more time in the mobile phase or the stationary phase. The chemicals that spend more time in the mobile phase than the stationary phase will move further.
- 15What is the End Result in Chromatography?The components in a mixture will normally separate through the stationary phase, so long as all the components spend different amounts of time in the mobile phase. The number of spots may change in different solvents as the distribution of the chemical will change depending on the solvent.
- 16How Many Spots Would a Pure Substance Form?A pure substance will only ever form 1 spot in any solvent as there is only one substance in the sample.
- 17During Paper Chromatography, what is the Stationary Phase and what is the Mobile Phase?The stationary phase is the chromatography paper (often filter paper) and the mobile phase is the solvent (e.g. ethanol or water).
- 18The Amount of Time the Molecules Spend in each Phase depends on what 2 things?How soluble they are in the solvent.
How attracted they are to the paper.
Molecules with a higher solubility in the solvent, and which are less attracted to the paper, will spend more time in the mobile phase - they'll be carried further up the paper. - 19The Result of Chromatography Analysis is called what?A chromatogram.
- 20What is an Rf value?The ration between the distance travelled by the dissolved substance (the solute) and the distance travelled by the solvent. The further through the stationary phase a substance moves, the larger the Rf value.
- 21What formula can you use to calculate the Rf value?Rf = distance travelled by substance / distance travelled by solvent
- 22Why is Chromatography often carried out?To see if a certain substance if present in a mixture. To do this, you run a pure sample of that substance (a reference) alongside the unknown mixture. If the Rf values of the reference and one of the spots in the mixture match, the substance may be present (although you haven't proved they're the same).
- 23What is the Rf value dependent on? Explain.The Rf value is dependent on the solvent - if you change the solvent the Rf value for a substance will change. You can test both the mixture and the reference in a number of different solvents. If the Rf value of the reference compound matches the Rf value of one of the spots in the mixture in all the solvents, then it's likely the reference compound is present in the mixture. If the spots in the mixture and the spot in the reference only have the same Rf value in some of the solvents, then the reference compound isn't present in the mixture.
- 24How do you Test for Chlorine Gas?Chlorine bleaches damp litmus paper, turning it white. (It may turn red for a moment first though - that's because a solution of chlorine is acidic.)
- 25How do you Test for Oxygen Gas?If you put a glowing splint inside a test tube containing oxygen, the oxygen will relight the glowing splint.
- 26How do you Test for Carbon Dioxide Gas?Bubbling carbon dioxide through (or shaking carbon dioxide with) an aqueous solution of calcium hydroxide (known as limewater) causes the solution to turn cloudy.
- 27How do you Test for Hydrogen Gas?If you hold a lit splint at the open end of a test tube containing hydrogen, you'll get a 'squeaky pop'. (The noise comes from the hydrogen burning quickly with the oxygen in the air to form H2O).
- 28What are Carbonates?Carbonates are substances that contain CO3 2- ions.
- 29How do you Test for Carbonates?Put a sample in a test tube. Use a dropping pipette to add a couple of drops of dilute acid. Then connect the test tube to a test tube of limewater. If carbonate ions are present, carbon dioxide will be released that will turn the limewater cloudy when it bubbles through.
- 30Give an example for reaction of carbonate with dilute acid
- 31What are Sulfate Ions?Sulfate Ions are substances that contain SO4 2-
- 32How do you Test for Sulfate Ions?Use dropping pipette to add a couple of drops of dilute HCl followed by a couple of drops of barium chloride solution (BaCl2) to a test tube containing mystery solution.
If sulfate ions are present, a white precipitate of barium sulfate will form. - 33Give the equation for the Test for Sulfate Ions
- 34How can you Test for Halide Ions?Add a couple of drops of dilute nitric acid (HNO3), followed by a couple of drops of silver nitrate solution, AgNO3, to your mystery solution.
- 35Give the results for the Test for Halide Ions
- 36How do you Carry out Flame Tests?Clean a platinum wire loop by dipping it in some dilute HCl and then holding it in a blue flame from a Bunsen burner until it burns without any colour. Then, dip the loop into the sample you want to test and put it back in the flame. Record the colour of the flame.
- 37Give the results for the Flame TestsLithium ions - crimson
Sodium ions - yellow
Potassium ions - lilac
Calcium ions - orange-red
Copper - green - 38What does the Flame Test only work for and why?For samples that contain a single metal ion. If the sample tested contains a mixture of metal ions, the flame colours of some ions may be hidden by the colours of others.
- 39Why can Metals Form a Coloured Precipitate with NaOH?Many metal hydroxides are insoluble and precipitate out of solution when formed. Some of these hydroxides have a characteristic colour.
- 40Explain the Test of Metals with NaOHAdd a few drops of sodium hydroxide solution to a solution of your mystery compound - in the hope of forming an insoluble hydroxide.
- 41Give the results for colour of the precipitates in the Test of Metals with NaOHCalcium - White
Copper - Blue
Iron (Fe2+) - Green
Iron (Fe3+) - Brown
Aluminium - White at first. But then redissolves in excess NaOH to form a colourless solution.
Magnesium - White - 42What happens during a Flame Emission Spectroscopy?A sample is placed in a flame. As the ions heat up their electrons become excited. When the electrons drop back to their original energy levels, they transfer energy as light.
The light passes through a spectroscope, which can detect different wavelengths of light to produce a line spectrum. - 43The combination of wavelengths emitted by an ion during Flame Emission Spectroscopy depends on what?Depends on the charge of the ion and its electron arrangement. Since no 2 ions have the same charge and the same electron arrangement, different ions emit different wavelengths of light. So each ion produces a different pattern of wavelengths, and has a different line spectrum.
- 44The intensity of the spectrum during Flame Emission Spectroscopy indicates what?The concentration of that ion in solution.
- 45Flame Emission Spectroscopy can be used to do what?Identify ions in solution and calculate their concentrations.
- 46Chemists often use instrumental analysis (i.e. tests that use machines), such as flame emission spectroscopy, instead of conducting tests. Why?Advantages of Using Machines:
Very sensitive - can detect even the tiniest amounts of substances.
Very fast and tests can be automated.
Very accurate.
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- Fichas sobre Chemical Analysis, creado por Jasmine Sillence el 07/02/2022.
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- Jasmine Sillence
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