Weighing containers

For reagent solutions as defined above (i.e. 1) it is usually sufficient to weigh out approximately the amount of material required, using a watchglass or a plastic weighing container, and then to add this to the required volume of solvent which has been measured with a measuring cylinder. 

Note Phosgene is eery hazardous and only professional chemists working with a fume hood should even think about using this method. It can be dissolved in a weighed container of DMF (dimethylformamide) and a second weighing will give the phosgene concentration. 

At first, before the pressure reaches 10-25 MPa, subquality emulsion is returned into reactor 3. After the operating pressure (30 MPa) has been established, quality emulsion is pumped into collector 8. The duration of homogenisation depends on the amount of emulsion mixture and the pressure in apparatus 6. The finished product from collector 8 is poured into readied and weighed containers. 

To find the molecular weight of any gaseous substance it is necessary therefore only to find the weight in grams of 22.4 liters of the gas under standard conditions. In actual practice it is not convenient to weigh containers which hold 22.4 liters. It is only necessary to know the weight of any volume and the conditions of the experiment. From these data the molecular weight can be calculated. 

Taring is the act of setting the scale to zero when a container is on the balance. Consequently, further weighings do not require subtracting the already-weighed container. 

General purpose balances which weigh to the nearest 0.01 g with a capacity of about 300 g. Chemicals may be dispensed for weighing, into a suitable weighing container, directly onto these balances. 

The most useful feature of this type of balance is the electronic zero facility (self-taring), which means the mass of the weighing container can be subtracted automatically before weighing chemicals. 

Place an empty weighing container (see p. 24) centrally on the balance pan and allow the reading to stabilize. If the object is larger than the pan, take care that no part rests on the body of the balance or the draught shield as this will invalidate the reading. Press the tare bar to bring the reading to zero. 

It is poof experimental technique to use i large containers to woiijli nut small masses you are atf mpliiui lo measure small differences between targe numbers For small masses use a small weighing container (Fig. 4.4). i. - . ... 

These come in various materials, shapes and sizes from glass weighing boats to beakers and even special glazed paper. The weighing container to be used depends on several factors ... 

Some of the common types of weighing container are shown in Fig. 4.4. 

Fig. 4.4 Weighing containers (a) plastic weighing dishes (b) weighing bottles (c) weighing boat.

Lock the balance,pan.by pressing the bar/button and remove /the-weighing container from the balance. --... 

Subtract the weight of the empty weighing container from p that of the weighing container plus sarnple and you now know the mass of cherqical, to an accuracy of four decimal places, f > which has Seen transferred into-your volumetric. flask/ Beaker.. -- oncbnical flask. - - I... 

The mass of a liquid is always obtained by difference. Liquids that are noncoiTO-sive and relatively nonvolatile can be transferred to previously weighed containers with snugly fitting covers (such as weighing bottles) the mass of the container is subtracted from the total mass. 

Weighing - never weigh anything directly onto a balance s pan you may contaminate it for others. Use an appropriate weighing container such as a weighing boat, sample tube, weighing paper, conical flask, beaker. 

Weighing paper - It is common practice to put a piece of paper onto the pan of general-purpose balances. The mass of the paper is then tared off before the weighing container is placed on the balance pan. The paper protects the balance pan from corrosion by spillages and also allows you to discard easily any material spilt without affecting the weighing. 

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