Basic laboratory techniques

Science 6

1. BASIC LABORATORY TECHNIQUES

2. Measuring Volume Place the graduated cylinder on a leveled working area. Make sure that the liquid meniscus is at eye level. For clear samples you should read at the lower meniscus and for dark-colored liquid samples, the upper meniscus .

3. USING PIPET Two types of pipet: 1. volumetric pipet – deliver specific amount of liquid sample 2. graduated pipet – deliver any amount of ample just like that of a graduated cylinder. Rubber aspirator – draw liquid sample into a pipet . Steps in using volumetric pipet: Fill in the pipet with the use of the rubber aspirator above the calibration mark. Remove the rubber aspirator and immediately cover the top of pipet with your index finger. Adjust the level of the meniscus by releasing slightly your right index finger. Drain freely the content of the pipet to the receiver by removing the right index finger.

4. Measuring mass Make sure that the measuring tray is free of any undesirable debris. Place all the riders to zero position and check if the pointer is aligned to the zero mark. If not, use the adjustment knob to position the pointer to zero. Do not place the chemicals directly on the balance pan. Place your samples on a weighing vessel or proper container. Moves first the hundreds rider. If the pointer drops below the zero marker, move the rider back to its original position. Do the same for the tens and the ones until pointer aligns to the zero marker. Read the mass of the sample by adding the positions of the rider.

5. 5. remove the sample and return to the original position. PARTS OF THE TRIPLE BEAM BALANCE

6. PROPER USE OF ANALYTICAL BALANCE Clean the balance before you weigh any sample. Do not place the chemicals directly on the balance pan. Place your sample on a weighing vessel or proper container. Make sure that the windows of the balance are closed before any measurement is made. The analytical balance has “ rezero ” or “tare” function. Place your weighing vessel on the pan and press this function. Wait for the digital readout 0.0000 before you add any chemicals. The digital readout that will appear will be the weight of the chemicals alone. Never weigh samples that are hot for they will damage the electronic parts of the balance. In determining the mass of liquid samples, do not add the sample while the vessel is inside the analytical balance. Always clean the balance after use.

7. USING THE BUNSEN BURNER Make sure that the rubber tubing connected to the gas inlet is secured and not damaged. Close the needle valve and the air ports and their parts after which connect the rubber tubing to the gas outlet. Have your matches ready before opening the gas outlet. Slowly open the needle valve to admit fuel and adjust the height of the flame as desired. At this point, the flame may be yellow and this is referred to as the “luminous flame”. A luminous flame is not used for heating purposes. A nonluminous flame or blue flame is ideal. To obtain a nonluminous flame, adjust the air port so as to admit more air that will mix with the fuel for complete combustion. Complete combustion will take place thus creating a nonluminous flame.

8. HEATING LIQUID SAMPLES - uses burner/alcohol lamp/heating man, and tripod, if using tripod needs wire gauze

9. TRANSFERRING REAGENTS FROM ONE CONTAINER TO ANOTHER SOLID Remove the cover of the reagent bottle (make sure that the cover dis not touch any surface. Use either porcelain or metal spatula to obtain sample. (corrosive chemicals must used porcelain spatula. If there is no spatula, simply tilt the reagent bottle around 45 o and rotating the bottle back and forth. Make sure that the receiver is clean to avoid contamination. LIQUID Use a dropper or pipet. Make sure that the tip of the dropper and the pipet did not touch the receiver bottle to avoid contamination. It can be also be poured to another container (CAREFULLY). A glass rod is used to guide the flow of liquid.

10. SEPARATION TECHNIQUES - Greatly used in separating mixtures - Mixtures contain two or more pure substances.

11. DECANTATION Fast means of separating liquid from heavier solid particles. The mixture is allow to stand for some time to allow the heavy particles settle down. Liquid (also known as decantate ), is slowly poured our to separate from the solid particles. Not applicable to solids that re light and fine.

12. FILTRATION Mixtures of solid and liquid can used this technique Applicable to lighter and finer solid particles. It uses filter paper

13. CENTRIFUGAT-ION Mixture that its solid particles are too small that even decantation and filtration cannot do the separation. Mixture is placed in a centrifuge tube and allowed to spin at a specific speed and time. The finer solid particles clump together at the bottom of the centrifuge tube and the liquid sample can be removed either with decantation or with the use of dropper.

14. DISTILLATION This technique is based on differences in boiling point of the components of the mixture. As the mixture is heated, the component with lower boiling point will evaporate, condense and collected in the receiving vessel first leaving behind the components with higher boiling point.

15. CHROMATO-GRAPHY Separates the components of mixtures based on the affinity of the components to two phases: the stationary and mobile phase. MOBILE PHASE – consists of the mixture and the solvent that moves the mixture through the column. STATIONARY PHASE – system in which the mobile phase flows and where the distribution of the components of the mixture occurs. Common type of chromatography is PAPER CHROMATOGRAPHY.

16. READING LABELS ON CHEMICAL BOTTLE THESE ARE THE GENERAL LABELS THAT NEEDS TO BE READ BEFORE USING THE CHEMICALS. Name of contents Chemical composition Statement of possible hazards and precautionary measures Instruction in case of Contact or Exposure Date prepared Manufacturer