Chem-Lab-Notes.pdf

Chem Lab notes: Centrifuge Safety Handling Chemical Safety: Equalize test tubes for balance Don’t try to stop it with your hand Work...

Chem Lab notes: Centrifuge Safety Handling Chemical Safety: Equalize test tubes for balance Don’t try to stop it with your hand Work with small containers (when transferring) Mix chemicals only when told to (go signal by the Dressing for Safety professor) Don’t wear extremely loose clothing Read and re-read chemical labels Wear sturdy natural fabrics Read instructions all the way through first Wear older clothes and a lab apron Use a work tray Wear long pants or long skirt Move carefully and deliberately Wear clothed leather shoes Add acid to water (a-z) Tie up long hair Hold coin-top stoppers while pouring Remove rings and watches Replace stoppers immediately Take out contact lenses Keep chemicals away from your face Cover your eyes with goggles with side shields Work with harmful volatiles under a hood Protect hands with right kind of gloves Keep chemicals pure and uncontaminated Use a pipette filler-never your mouth Behavior in Lab Put waste in a proper container Don’t fool around Clean up when finished Keep aisles clear Bunsen Burner and Glassware Safety Stand on step stool Keep make up in purse Heat volatiles in a heating mantle or a steam Keep food and drinks outside bath in a hood Check gas hose for cracks Emergency Equipment Fit hose securely on gas valve and Bunsen burner Clean and dry cut Stand back while lighting Rinse eyes in eyewash fountain Strike matches away from you Rinse hands and arms in sink Turn on gas after lighting the match (light on the side) Remove clothes and rinse large spills in safety shower Turn gas off if flame sputters, flares, goes out or if you smell goes Cover small fires Check glassware for stars or cracks Let teacher handle larger fires Clamp narrow necked containers Put out clothing fires in safety shower Move test tubes back and forth at an angle Use fire blanket carefully to keep flames away from face and neck Don’t heat closed containers Hold hot glassware in beaker tongs or hot mitts Protecting Yourself Thermometer Safety: PPE Lab coats must be fastened Don’t shake the thermometers Avoid loose clothing Use thermometers in suitable temperature range Don’t wear sandals or open shoes, and skimpy Lay thermometers on towel or wire screen away clothing from edge Long hair should be tied Let teachers clear up broken thermometers Safety goggles – for chemicals, glass or heat. Gloves- remove before using instruments, Class Tubing Safety telephone, and leaving the laboratory Use an inserter Lubricate tubing and wear leather gloves Laboratory hygiene Never eat, drink or smoke laboratory Don’t apply cosmetics Avoid touching of eyes, face, and mouth. Always wash your hands before you leave and before eating. General Hazards Fire Breakage of glassware Sharps Spillages Pressure equipment & gas cylinders Extremes of heat & cold Chemical hazards Biological hazards Radiation Heat test tubes at an angle directing the opening Always ADD ACID to water oppositely to you and other people in the laboratory. Don’t smell any chemicals directly – use hands for whiff Do not pipet solutions by mouth – use a rubber suction or other device to fill a pipet Spillages- clear up spillages. Dispose hazardous toxic waste Remember that the lab is a place for serious work Wash your hands with soap and water before leaving Electrical equipment – always do a visual check on electrical equipment, never use defective equipment AVOIDING FIRES General tidiness Keep your workplace tidy. Clear up waste, deal with washing up and put things away as you finish with them (CLAYGO) Make sure everything is safe before you leave things unattended A tidy laboratory avoids accidents to everyone Waste Materials Dispose of waste lab materials safely Do not put materials down the drain or in with normal waste unless athorised Laboratory Equipment Never use any laboratory equipment unless you are trained & have been authorised to do so.  As well as injuring yourself you may cause very costly damage First aid All laboratory worker should undergo simply first aid training. o all chemical splashes should be washed 15-20 minutes o control bleeding with direct pressure, avoiding any foreign bodies such as glass always report accidents to instructor.  Measurement in Chemistry Laboratory Two Types of data: Qualitative Data Descriptive, non-numerical data Ex. Color, phase, texture Quantitative Data Numbers with units Ex. 10mL, 5g International System (SI) – units is the standard units of measurement used by scientists and scientific works. Accuracy – the closeness of the observation or measured value value to the true value. Precision – closeness of a set of true values obtained from identical measurement of something. Error Uncertainty Does not mean ‘mistale” Describe both imprecision and inaccuracy collectively. Categories Systematic errors  o Difference between an observation and the true value that are consistent form one observation to the next Random errors o They are unpredictable and change from one observation to another. Percent Error Expresses error as a percentage of the accepted value. Error can be either positive or negative. Positive error means that the measured value was larger than the real/accepted value value. Negative means that the measured value was smaller than the are value value Use the absolute value for percent error. Recording Measurements Significant figures. Any number in a measurement that is known with certainty plus one which is an estimated number. Significant Figures Rules Laboratory Measurement Density  Stoichiometric Calculation determine the amount of salt in seawater, or to determine the mass of the counter-ion of an unknown The Alkaline Earth Metals chloride compound. But the analyte could also bean The elements of the main group 2 of the periodic table other ion. are called the alkaline earth metals. The constituents of The analyte is reacted with a counter-ion with which it the group are Beryllium (Be), Magnesium (Mg), Calcium forms an insoluble compound, which can then be (Ca), Strontium(Sr), Barium (Ba) and Radium (Ra). isolated and weighed. From the mass of the precipitate Common for the elements of this group is that they are the amount of the analyte can be calculated. If the metals in their pure form, with low densities and low analyte is the chloride ion, then the counter-ion could be melting and boiling points. They all react with halides (F, silver, Ag⁺, because AgCl is insoluble in water. Cl, Br, I) to form metal halides. Since the number of valence electrons of the alkaline earth metals is 2, the general formula of the formed metal halides is MX₂, where M is the metal and X is the halide. All of the alkaline earth metals occur naturally, although Radon only occurs as a decay product from Uranium or Thorium, and is highly radioactive. Magnesium and Calcium are both among the top-8 most abundant elements on the Moles and Avogadro’s number earth’s surface. Balancing chemical equation A chemical equation shows what happens in the chemical reaction. The basic chemical reaction can be written as follows: In a balanced equation, the total number of atoms of each kind (e.g. A) in the reactants and products is the same. Calculating molecular weights The relationship between the different components of the reaction is referred to as the reaction stoichiometry. The relationship between M, m and n The number of moles, n, of a substance can be found by using the following equation Gravimetric analysis Where m is the mass and M is the molecular weight if Gravimetric analysis is a technique to determine the the given substance. amount of an analyte based on mass. A common example of a gravimetric analysis is to determine the amount of chloride in a solution - for example, to The molecular weight, M or Mw, is the mass in grams per percentage of the theoretical yield you obtained in a one mole (g/mol or gᐧmol⁻¹) of a substance. It can be given experiment. It is calculated by: calculated from the atomic weights of its constituent atoms, but when you look at the unit (g/mol) you can see that it can also be calculated if you know the mass of a substance (g) and how many moles that corresponds to In most cases, when the yield of a reaction is mentioned (mol). without referring to either theoretical, experimental or percentage yield, it is implicitly the percentage yield that is meant. Conversion between moles of molarity By rearranging this equation you can also calculate how many grams, a certain number of moles should weigh, by When a compound is dissolved in a solvent the isolating m in the equation: concentration of the compound is usually given in moles per liter (mol/l or mol·l⁻¹) which also called molarity, M. To calculate how large a volume, V, of a solution with a known concentration, c, to use in order to obtain a certain number of moles, n, the following equation is used. Limiting and excess reagents The equation can be rearranged to isolate for n or c if it should be desired. In the chemical equation where we form water from hydrogen and oxygen, we can see that hydrogen and Experimental thoroughness and accuracy. oxygen reacts in a 2:1 ratio. This means that if you have two moles of hydrogen molecules and one mole of When performing chemical experiments in the oxygen molecules, you have stoichiometric amounts of laboratory a great deal of thoroughness and accuracy is the reagents, and you form two moles of water. necessary if you want to obtain reliable and reproducible results. It is important when you are performing a reaction that you measure accurate amounts of reactants to ensure the highest possible conversion, and thoroughness when you isolate your product, to minimize the loss and achieve the highest possible yield. It is even more crucial when you are performing When calculating the theoretical yield of your reacting, experiments within analytical chemistry. Here, you have to take into account which is the limiting sloppiness will not just lead to a poor yield, but can lead reagent. to a wrong conclusion to the analysis. Theoretical, experimental and percentage yield The theoretical yield of a reaction is the amount of product you would get if you use up all of the limiting reagent, and if there is no loss, e.g. by degradation of reactant or product or by formation of byproducts. The experimental yield is the actual amount of product you obtain when performing a given experiment. The percentage yield is a calculation of how large a