CHM 107 PDF - Laboratory Apparatus, Hazard Symbols & Safety

Okay, here is the converted information of the image or document into a structured markdown format: ### LABORATORY APPARATUS #### Laboratory Apparatus and their Uses **Beakers:** They are used as a reaction container or to hold liquid, solid samples or chemicals in the laboratory. They are also...

Okay, here is the converted information of the image or document into a structured markdown format: ### LABORATORY APPARATUS #### Laboratory Apparatus and their Uses **Beakers:** They are used as a reaction container or to hold liquid, solid samples or chemicals in the laboratory. They are also used as collectors of liquids during titrations and filtrates form filtration. **Bunsen Burner:** Bunsen burner is a specially prepared burner in which natural gas is used as a fuel for burning. It is used for heating various chemicals, solutions etc. **Reagent Bottles:** Reagent bottles are used to store liquid reagents. **Crucible:** A crucible is a cup-shaped piece of laboratory equipment used to contain chemical compounds when heated to extremely high temperatures. The lid covers the bowl so nothing escapes, or to keep oxygen out of the reaction. It is used to take and handle small quantities of solid chemicals. **Wash Bottle:** A wash bottle is used for dispensing small quantities of distilled water. **Volumetric flask:** A volumetric flask is used to measure precise volumes of liquid or to make precise dilutions. **Tripod stand:** To put containers above especially when heating above a Bunsen burner. **Retort Stand and Clamp:** A retort stand is used for holding pieces of glassware in place with the aid of clamp(s). **Test tube Rack:** A test tube rack is used for holding test tubes containing chemicals waiting for further operations. **Test tube Holder:** A test tube holder is used for holding test tubes when tubes should not be touched. **Safety Glasses:** Safety googles are used to protect the eyes in the laboratory. **Wire Gauze:** A wire gauze is used to spread heat of a burner flame and also supports beakers to be heated by Bunsen burners. **Round-Bottomed Flask:** A round-bottomed flask is used for carrying out reactions at high temperature. **Flat-Bottomed Flask:** A flat-bottomed flask is used for storing solution and carrying out reactions at room temperature. **Funnel:** A funnel is used to transfer solids and liquids without spilling and also used or for filtering when equipped with filter paper. **Burette:** A burette is used to dispense known amount of a liquid reagent in experiments for which precision is necessary such as titration experiments. **Pipette:** A pipette is a laboratory apparatus used intransporting a measured volume of liquid. There are different types of pipettes such as glass pipettes, piston-driven pipettes etc. **Pasteur Pipette:** Pasteur pipette is also known as teat pipette or dropper. It is made of plastics or glass and is used to transfer small amounts of liquids. It is not graduated or calibrated. It is used for addition of liquids, drop wisely. **Erlenmeyer Flask (Conical flasks):** Erlenmeyer flasks are often used in chemistry for titrations. They are also often used to heat liquids. The Erlenmeyer is usually graduated on the side to indicate the approximate volume of contents. It is different from a beaker in its tapered body and narrow neck. The conical shape allows the contents to be swirled or stirred during an experiment, either by hand or by a shaker; the narrow neck keeps the contents from spilling out. **Cuvettes:** A cuvette is a small tube of circular or square cross section, sealed at one end, made of plastic, glass, or fused quartz (for ultraviolet light) and designed to hold samples for spectroscopic experiments. **Measuring Cylinder:** A measuring cylinder is laboratory glassware used for approximate measurements of liquids. It is also used to measure volumes of objects by water displacement methods. **Mortar and Pestle:** A mortar and pestle is a tool used to grind and mix substances, including chemicals in the laboratory. The pestle is a heavy stick, made from porcelain, wood or other materials, whose rounded end is used for pounding and grinding. The mortar is a bowl, which can be made from porcelain, wood, carved stone or other materials. The substance is ground between the pestle and the mortar by rubbing or pounding the substance with the pestle against the wall of the mortar, thus turning it into a fine powder. ### HAZARD SYMBOLS Hazard symbols are symbols that are designed to warn about hazardous materials. These symbols are easily recognized. Some common hazard symbols are listed below. You must be able to recognize these symbols and explain their significance. Before using any material in the laboratory, look out for the symbol on it. * **Oxidizing:** Substances with this symbol are highly oxidizing. They provide oxygen and consequently allow other materials to burn more fiercely. * **Flammable:** Substances with this symbol catch fire easily. * **Toxic:** This symbol (skull-and-crossbones) is often used to denote danger. It is usually used for poisonous materials. Substances with this substance can cause death when swallowed, breathed in or when absorbed through the skin. * **Harmful:** Substances with this symbol are similar to toxic substances but they are less harmful. * **Corrosive:** Corrosive substances destroy living tissues, including the eyes and skin. When such substances get in contact with the eye or skin, they should be washed quickly with clean water. * **Irritant:** Substances with this symbol are not corrosive but they can cause reddening or blistering of skin. * **Radioactive:** Substances with this symbol contain hazardous quantity of radioactive materials. ### Units of Measurement A system of measurement must be defined in order for people around the world to agree on quantitative observations. Le Systéme International (SI) system, also known as the metric system is used by scientists all around the world for this purpose. The fundamental units of the SI system are listed in the table below | Physical Quantity | Name of Unit | Abbreviation of Unit | | :------------------- | :----------------------- | :------------------- | | Mass | kilogram | kg | | Length | meter | m | | Time | second | s | | Temperature | Kelvin | K | | Electric current | ampere | A | | Amount of substance | mole | mol | | Luminous intensity | candela | cd | Most often, the fundamental units are not convenient to use, therefore prefixes are used to change the size of the unit. Some common prefixes are listed below ### PRACTICAL ONE #### INTRODUCTION Before performing any experiments in the laboratory, the following rules should be read and understood by every student. Read and follow all instructions strictly before proceeding with any experiment. **- SAFETY RULES AND HAZARD SYMBOLS** **SAFETY RULES** **GENERAL** 1. Do not eat, drink or smoke in the laboratory under any circumstances. 2. Always keep your working area clean and tidy and free of clutter. 3. Always keep benches tidy. 4. Do not put solids in sinks to avoid blockage. 5. Always close cylinder valves after use. Make sure you know where to turn off the gas. 6. Always label containers in plain English with the known name of the substance and the appropriate hazard warning symbol. 7. Always secure the tops of reagent bottles immediately after use. 8. Never use your bare hands to transfer chemicals. Use a spatula instead. 9. Never smell gases directly - fan a little of the gas towards the nose instead. 10. Always handle concentrated acids and alkalis with great care. 11. Don't haphazardly mix chemicals! Pay attention to the order in which chemicals are to be added to each other and do not deviate from the instructions. 12. Always read the label on a reagent bottle carefully to make sure it contains the chemical you want. Put the bottle in its original place immediately after use. 13. Always work with fume cupboard sashes as low as possible and always work towards the back of the cupboard. 14. Always clear up spillages immediately they occur. 15. Do not leave equipment using water, gas or electricity on overnight without completing a "Silent Running" form, and always ensure all water hoses are secured with jubilee clips. **HYGIENE** 1. Do not pipette by mouth. 2. Always wash hands after using any substances hazardous to health, on leaving the laboratory and before visiting the toilet. 3. Do not touch surfaces (phones, door handles etc) with your contaminated gloves if they will be touched by others. **Handling Chemicals Safety Summary Lab Rules** * Work with small containers. * Mix chemicals only when your teacher says so. * Read and reread chemical labels. * Read instructions all the way through first. * Use a work tray if your lab has them. * Move carefully and deliberately when handling chemicals. * Add concentrated sulfuric or phosphoric acid to water. * Hold coin-top stoppers between your fingers while pouring. * Hold bottles with your hand over the label. * Replace stoppers immediately. * Keep chemicals away from your face. * Work with harmful volatile chemicals under a good. * Keep chemicals as pure and uncontaminated as possible. * Draw our chemicals with a pipette filter - never by mouth. * Notify your teacher to clean up spills. * Put waste in the proper container. * Clean up your work bench when finished **Thermometer Safety Summary Lab Rules** * Don't shake thermometers. * Use thermometers only in the range they're suited for. * Lay thermometers down on a towel or wire screen to cool, away from the edge of the bench. * Let your teacher clean up broken thermometers. **Glass Tubing Safety Summary Lab Rules** * Use an inserter to place glass tubing in a stopper or remove it. * Or, lubricate the tubing and protect your hands with leather gloves. **Centrifuge Safety Summary Lab Rules** * Place equally filled test tubes in a centrifuge to balance it. * Don't try to stop the spinning with your hand. Dressing For Safety Summary Lab Rules * Don't wear extremely loose clothing. * Fabrics should be sturdy and natural. * Wear older clothes and coyer them with a lab apron. * Wear long pants or long skirts to cove your legs * Wear closed leather shoes to protect your feet. * Tie up long hair. * Remove rings and watches. * Take out contact lens * Cover your eyes with goggles with side shields. * Protect your hands with the right kind of gloves. Behavior in the Laboratory Summary Lab Rules * Don't fool around in lab. * Keep aisles clear of personal belongings. * Stand on a step stool when you have to reach. * Keep makeup in your purse. * Keep food and drinks outside **Bunsen Burner and Glassware Safety Summary Lab Rules** * Heat volatile organics in a heating mantle or steam bath in a hood- not over Bunsen burner. * Check the gas hose for cracks. * Make sure the hose fits securely on the gas valve and Bunsen burner fittings. * Stand back from the burner while lighting it. * Strike matches away from you. * Turn on the gas after lighting the match.. * Turn the gas off immediately if the flame sputters, flares, or goes out, or if you smell gas. * Check glassware for stars or cracks. * Clamp narrow-necked containers to the ring stand. * Move test tubes back and forth through the flame at the angle while heating. * Don't heat closed containers. * Hold hot glassware in beaker tongs or hot mitt. **Emergency Equipment Summary Lab Rules** * Clean and dry the skin around a cut before a bandage is applied. * Rinse chemicals from your eyes in the eyewash fountain. * Rinse chemicals from your hands and arms with water in the sink. * Remove your clothes on the way to safety shower to rinse large spills from your body. * Extinguish small fires in containers by covering them. * Let your teacher use an extinguisher to put out large fires. * Put out clothing fires in the safety shower. * If there's no other way to put out a clothing fire, use a fire blanket carefully to keep flames away from the face and neck. **Demonstrating Safety Equipment** Students must know the location of each piece of safety equipment in the lab as following: * SAFETY SHOWER. Activate the shower. Use a large container to catch the water. Make sure you know how to shut off the water * WORK TRAY. Spill water on the tray, and show that the spill is contained * EYEWASH. Push the bar or lever on the eyewash fountain * FIRE EXTINGUISHER Stress that only you may use the fire extinguisher. Briefly demonstrate how to use it. Be sure to get it recharged * FIRE BLANKET. Pull the fire blanket out of its box, and demonstrate dropping it on top of a prone body * FUME HOOD. Light incense or a smoke candle inside the fume hood. Have a student lower the glass door and turn on the fan. Watch as the smoke is drawn away from the classroom * FIRST AID KIT. Have a student open the first aid cabinet and remove a box of bandages .Open the box to make sure there are bandages in it, and show the content to the class. Then return the bandages to the cabinet Fill in the blank. 1. Pour chemicals from large reagents bottles into \_\_\_\_\_\_ before measuring. 2. Read and \_\_\_\_\_\_ a chemical label before using the chemical. 3. When diluting an acid, always add \_\_\_\_\_\_ to \_\_\_\_\_\_ . 4. Work with volatile chemicals under a \_\_\_\_\_\_ 5. Use a \_\_\_\_\_\_ or \_\_\_\_\_\_ draw liquid into a pipette. 6. Strike matches \_\_\_\_\_\_ your body. 7. Move test tubes back and forth at an \_\_\_\_\_\_ while heating. 8. Hold hot glassware \_\_\_\_\_\_ with \_\_\_\_\_\_ or \_\_\_\_\_\_ 9. When inserting lubricated glass tubing into a stopper, protect your hands with \_\_\_\_\_\_ 10. Always protect your eyes with \_\_\_\_\_\_ when working in the laboratory. 10. Stand on a \_\_\_\_\_\_ if you need to reach. 11. Rinse chemicals from your eyes in an \_\_\_\_\_\_ 12. \_\_\_\_\_\_ clothing on the way to the safety shower. 13. Extinguish small fires in containers by \_\_\_\_\_\_ them. 14. Put out clothing fires in a \_\_\_\_\_\_ ### PRACTICAL TWO #### MEASUREMENT AND DENSITY Density of a substance is defined as its ratio of mass to volume., there are different dimensions as lb/ft³ or g/cm³ (which is the same as g/mL). The density of an element or compound is a characteristic physical property at a specified temperature and atmospheric pressure and is therefore useful in identifying the substance. In the general chemistry laboratory, density is most often determined by finding both the mass and volume of a substance, independently, and calculating the density by dividing the mass by the volume. Mass determinations are easily accomplished by weighing a sample on a balance. However, the determination of volume is not always straightforward and methods may vary in accord with the nature of the sample. For instance, if the solid is a large object of regular shape, such as cubic or cylindrical, one can measure its dimensions and calculate the volume from the appropriate formula ($V = s^3$ for a cube and $V = \pi r^2 h$ for a volume of the water displaced (according to Archimedes' Principle, the volume of the liquid displaced is equal to the volume of the object which does the displacing). If the sample is composed of small particles, as sand and table salt are, one might be tempted to fill a graduated cylinder with sample and read the volume from the calibration marks. This could lead to a large error in the determination of the volume because such granular samples have a considerable amount of empty space between particles. A more accurate determination of the volume of such samples may be obtained by adding a known volume of liquid to the sample, stirring to ensure mixing of the solid and the liquid, and reading the total volume of the mixture from the calibration marks. The actual volume occupied by the particles of granular solid is then determined as the difference between the total volume (of the liquid plus solid) and the volume of the liquid alone. This method is effective as long as the solid does not dissolve in the liquid. **PRELAB EXERCISES:** 1. Why should weighing data, or any other measurement data should, be recorded immediately in your laboratory manual and not on a scrap of paper? 2. An object was carefully weighted five times on a chemical balance. The masses were: 11.36g: 11.37g: 11.40g: 11.38g: and 11.39g. a. Calculate the average value of these measurements. b. Calculate the standard deviation, s.d., of this set of measurements using the range of the data and the square root of the number measurement averaged. (please show all work) 3. Calculate the density of a solid if it has a mass of 8.47g and a volume of 3.24$cm^3$.. Please show your calculations, with units, below. #### RECORD SHEET **A. MEASUREMENT AND DENSITY** 1. Measuring the mass of a solid and determining the quality of a balance Unknown number \_\_\_\_\_\_\_\_\_\_\_\_\_\_\__\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ Mass of unknown (first weighing):\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ (Reminder: significant figures and units) Mass of unknown (second weighing):\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ Mass of unknown (third weighing):\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ Average mass of the unknown:\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ Highest measured mass:\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ Lowest measured mass:\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ Standard deviation of the averaged value:\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ **B. MEASURING THE VOLUME OF A LIQUID** 1. Which volume is represented by the nearest (closed spaced) division on your graduated cylinder? \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ 2. Number of drops to increase volume by 1.0ml: \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ (e.g. from 15.0ml to 16.0ml or from 3.0ml to 31.0ml) Number of drops to increase volume by 1.0ml: \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ (from 16.0ml to 17.0ml or from 31.0ml to 32.0ml) Number of drops to increase volume by 1.0ml: \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ (from 17.0ml to 18.0ml or from 32.0ml to 33.0ml) 3. Average number of drops per millimeter: \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ (please show calculations below) **C. DETERMINING THE DENSITY OF A SOLID** Density Unknown Number Accompany each measured and calculated value with the correct unit. | | Trial II | Trial II | | :---------------- | :------------------------------- | :------------------------------- | | 1. Mass of Density Unknown: | \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ | \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ | | 2. Burette reading (before adding density unknown): | \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ | \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ | | 3. Burette reading (after adding density unknown): | \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ | \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ | | 4. Volume of density unknown: | \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ | \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ | | 5. Density of unknown: | \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ | \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ | (show all calculations below with units; state the answer to 3 significant figures) #### PRACTICAL THREE **DETERMINATION OF THE FORMULA OF A HYDRATE** **INTRODUCTION** Compounds that firmly held water molecules into its solid structure are called Hydrates. A defined number of water molecules are associated with each formula unit of primary material in hydrates. The water presence in the hydrate is referred to as **water of hydration**, this can be removed by heating, after removal of water the left over is said to be anhydrate or anhydrous. Hydrates formulas shows the fixed water content in their crystals. **Examples** Calcium chloride, $CaCl_2 \cdot 4H_2O$, clearly shows that four molecules of water are associated with each formula unit of calcium chloride named Calcium chloride tetrahydrate. Copper (II) sulfate shows that 5 molecules $CuSO_4 \cdot 5H_2O$ of water are present for each mole of copper (II) sulfate, and it is named copper (II) sulfate pentahydrate. Some salt can form more than one hydrate. Cobalt (II) chloride $CoCl_2$, forms a red hydrate with the formula $CoCl_2 \cdot 6H_2O$ cobalt (II) chloride hexahydrate and a violet hydrate, which is $CoCl_2 \cdot 2H_2O$ cobalt (II) chloride dihydrate. The mole ratio of water to salt is revealed in their names. Most hydrates will lose their water of hydration when heated strongly, leaving the anhydrous (water- free) salt behind. Some hydrate display a color change as the water is lost $CoCl_2 \cdot 6H_2O \xrightarrow{-4H_2O} CoCl_2 \cdot 2H_2O \xrightarrow{-2H_2O} CoCl_2$ Red violet blue The loss of water by a hydrate is reversible. If the anhydrous salt is exposed to moist air or some other source of water, it will regain the water of hydration. The property of reversibility can be used to distinguish true hydrates from other compounds that produce water when heated. The hydrate can be reformed from the anhydrous salt by the addition of water. In this experiment, you are to determine the percent water in hydrate obtained from your instructor. If you do this, you will be given the general formula of the hydrate as "salt.xH2O" with this formula and the percent water, you can then calculate the value of and complete the formula of the compound. The following equations summarize the calculation required in this experiment: 1. **CALCULATING THE PERCENTAGE OF WATER IN HYDRATE** The percent water by mass in a hydrate is determined by dividing the mass lost by the hydrate with heating by the mass of the original sample. Multiplying this fraction by 100% will give the percentage water in the hydrate. Mass of hydrate sample= (mass of crucible + unknown) - (mass of crucible + lid) Mass of water driven off = (mass of crucible + unknown) - (mass of crucible + residue after final heating) Percent $H_2O = \frac{mass \space of \space water \space driven \space off}{mass \space of \space hydrate \space sample} \times 100%$ 2. **Calculating the formula of a hydrate** Here you are to calculate the value of x in the formula of the hydrate, salt x H20. x is determined by dividing the number of mole of water lost by the hydrate sample by the number of salt in the sample. Since this is the moles of salt without the water of hydration it will be called the anhydrous salt. Your instructor will give you the formula of the anhydrous salt, and from this you can calculate its formula mass, you can convert the mass of the anhydrous salt to moles of the anhydrous salt. The formula mass of water, $H_2O$, is 18.0g/mole. Mass of anhydrous salt = (mass of crucible + lid + residue after final heating) - (mass of crucible + lid) Moles of anhydrous salt in sample = $\frac{mass \space of \space anhydrous \space salt}{Formula \space mass \space of \space anhydrous \space salt}$ Mole of water in hydrate sample = $\frac{mass \space of \space water \space driven \space off}{Formula \space mass \space of \space water}$ $X =\frac{moles \space of \space water \space in \space hydrate \space sample}{Moles \space of \space anhydrous \space salt \space in \space sample}$ The formula of the hydrate is then saltxH20 * **PRELAB EXERCISES:** 1. How would you test a colourless crystalline compound to determine if it was a hydrate? . 2. Cobalt (11) chloride is commonly obtained from chemical supply houses as a hydrate with the formula CoCl2.6H2O. An analysis showed that 25.0g of this hydrate contains 11.3g of water. What is the percent water by weight in this hydrate? 3. Why is it necessary to heat the hydrate gently at first and then more strongly only after most of the water has been driven off? 4. A 0.940g sample of barium chloride dehydrate is heated and 0.800g of anhydrous residue remains after cooling. 5. How many moles of anhydrous barium chloride were present in the sample? 6. How many moles of water were present in the sample? * **EXPERIMENTAL PROCEDURE:** 1. **Determining the percent water and the formula of a hydrate** 2. Collect a crucible from your instructor label as your group alphabet, record on the report sheet, handle the crucible with crucible tongs. 3. Determine the mass on a zeroed balance. Record the mass on the report sheet to the maximum accuracy allowed by the balance. Use the same balance for all weighing. 4. Obtain the unknown hydrate into the crucible 5. Put the entire sample of the unknown hydrate in the crucible. Weigh the crucible + unknown to the maximum accuracy of the balance and record this mass on the Report sheet. 6. Place the crucible inside an oven and heat for 12 to 15 minutes. If heated too strongly for several minutes, some hydrate may decompose beyond the simple loss of water. After the allotted time, return the crucible to the wire gauze and let it cool to room temperature. When it is cool, weigh the crucible + residue to the maximum accuracy of the balance and record this mass on the Report sheet as the "after first heating" entry. 1. Repeat the heating - cooling- weighing cycle a second time, this time heating the crucible to about ten minutes. Record this mass on the Report sheet as the "after second heating" entry. 2. Repeat the heating-cooling-weighing sequence until two successive weighings agree within ± 0.040g. When this occurs you can be confident that all the water has been driven out of the hydrate and only anhydrous salt remains. Use this final mass in the calculations. 3. Calculate the percentage of water in the unknown hydrate. Show all calculations clearly on the back of the report sheet. $Percent \space H_2O = \frac{mass \space of \space water \space driven \space off}{Mass \space of \space hydrate \space sample} \times 100%$ 4. Calculate the number of moles of water lost by the hydrate as it was heated. Calculate the number of moles of anhydrous salt remaining in the crucible. Record both values on the report sheet. Then calculate the value of x in the formula of the hydrate. $X= \frac{mol \space of \space water \space in \space the \space hydrate \space sample}{mol \space of \space anhydrous \space salt \space in \space sample}$ Show all calculations on the back of the report sheet. #### RECORD SHEET **DETERMINATION OF THE FORMULA OF A HYDRATE** * Unknown number: * Mass of crucible + lid + unknown * Mass of crucible + lid * Mass of unknow hydrate * Mass of crucible + lid + residue... * .....after first heating * ......after second heating * .......after third heating * Mass of anhydrous salt * Mass of water lost * Percent water in unknown hydrate * Formula of unknown hydrate (from your instructor) * Moles of water in the hydrate sample * Moles of anhydrous salt in the hydrate sample * Complete formula of the hydrate #### PRACTICAL FOUR **GRAVIMETRIC ANALYSIS** **Introduction** Gravimetric analysis is concerned with the process of producing and weighing a compound or element in as pure a form as possible after some form of chemical treatment has been carried out on the substance to be examined. The mass of the element, ion or radical in the original substance can be readily determined from the knowledge of the formula of the compound and the relative atomic masses of the constituent elements. It deals with the measurement of the mass of a substance produced or left at the end of a chemical conversion. In this experiment, the amount of sulphuric acid present in a given solution will be determined gravimetrically by reacting the acid with barium chloride. The amount of the acid can be obtained by weighing $BaSO_4$ produced during the reaction. The equation of the reaction is $H_2SO_4 + BaCl_2 \longrightarrow BaSO_4(s) + 2HCl (aq)$ $BaSO_4$ is suitable for this gravimetric determination because its precipitate is (i) readily and completely formed from the solution being analyzed. (ii) pure and easily filtered (iii) a solid of known composition and its molar mass is sufficiently large that an appreciable and easily weighed mass of precipitate will be produced * **PRELAB EXERCISES:** 1. Distinguish between a gravimetric and volumetric method of analysis. 2. Mention three advantages offered by gravimetric analysis. 3. An excess of $BaCl_2$ is added to 5.00ml of a 0.250 M $H_2SO_4$ solution. What will be the mass of the resulting precipitate? 4. **Experimental Procedures** Measure out 10ml of 0.5M $BaCl_2$ into a 100ml beaker. Warm this solution for about 10 minutes on water baths or hotplate \[DO NOT HEAT TO DRYNESS]. While the above solution is being heated, measure 5ml of the $H_2SO_4$ solution given into another 100ml beaker and add 5ml of 1M HCl solution to it. This ensures that large particles of precipitate are formed. Heat this solution for about 5 minutes (Don't heat to dryness). Remove the two solutions from water bath and slowly add the $BaCl_2$ solution into the beaker of $H_2SO_4$ solution when the two are still hot. Stir vigorously but add the $BaCl_2$ slowly to ensure that large particles are formed. Rinse the stirring rod with distilled water before removing it from the beaker. Filter the mixture using a pre-weighed filter paper placed in a funnel. Wash the precipitate from the stirring rod and the beaker with distilled water. Carefully transfer the wet filter paper from the funnel onto a clean dry paper and dry in the oven. Repeat the procedure above for a second determination. Record your report following the pattern shown below #### RECORD SHEET **GRAVIMETRIC DETERMINATION OF SULPHATE ION** | | TRIAL 1 | TRIAL 2 | | :---------------- | :------------------------------ | :------------------------------ | | Mass of filter paper (g) | \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ | \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ | | Mass of $BaSO_4$ and filter paper (g) | \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ | \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ | | Mass of $BaSO_4$ precipitated (g) | \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ | \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ | Average mass of $BaSO_4$ precipitated Moles of $BaSO_4$ precipitated Concentration (in mol.$dm^{-3}$) of $H_2SO_4$ used for precipitation. **VOLUMETRIC ANALYSIS (TITRIMETRIC ANALYSIS)** **Introduction** Volumetric analysis is a technique for determining the concentration of a solution by measuring volumes of solutions. Volumetric analysis is usually achieved by adding a solution of known concentration (standard solution) to another solution until the chemical reaction between the two solutes is complete. In titration, a measured volume of one solution is placed in a conical flask and the other solution is added from the burette. As the solution is gradually added from the burette, a point is reached when the reaction would have occurred exactly according to the stoichiometry of the reaction and none of the reagents will be present in excess. This is called the stoichiometry point or equivalence point. The stoichiometry point is identified by adding an indicator- an organic compound which changes colour in the presence of excess of the added reagent. **APPARATUS AND TECHNIQUE** **(a) STANDARD FLASK** A standard flask is designed to contain a definite volume when filled to the calibration mark. It must not be heated or filled with hot solution; any solution it is to contain must be at room temperature. **(b) PIPETTE** A pipette is designed to deliver a fixed volume of liquid when correctly filled to the calibration mark. Before use, the pipette must be washed with detergent solution, tap water and distilled water. Finally the pipette must be rinsed with the solution it is to measure. This is done by pouring some of the solution into a clean dry beaker and sucking sufficient solution from the beaker into the pipette to fill its lower stem. Hold the pipette horizontal and rotate it gently so that the solution washed the bulb and upper stem up to above the calibration mark. Allow the wash solution to drain. Rinse at least a second time. To fill the pipette place the tapered-end well below the level of the solution and suck the solution to a point above the calibration mark using a pipette teat. Retain the solution in the pipette by placing a dry forefinger on the mouth-piece. Remove the pipette from the solution and allow the surplus solutions on the outside to drain away. Bring the solution level down until the meniscus just touches the calibration mark by gently releasing the fore-finger. Then allow the solution to run unto a conical flask when all the solution has run out, allow the pipette to drain for 30 seconds, keeping the tip contact with the side of the conical flask for about