How to weigh a solid or liquid in organic chemistry laboratory
How to weigh a solid?
To weigh a solid, you will need:
- A balance scale with a digital display
- Weighing boat, crinkle cup, or diagonally folded glazed weighing paper
- The solid reagent you want to weigh
Here are the steps to weigh a solid:
- Place the weighing boat, crinkle cup, or weighing paper on the balance pan.
- Press the "zero" or "tare" button on the balance scale to set the reading to zero with the weighing boat, crinkle cup, or weighing paper on the pan.
- Use a spatula to add small portions of the solid reagent into the weighing boat, crinkle cup, or weighing paper until the desired mass (within 1-2% of the specified amount) is shown on the digital display.
- Record the actual amount used in your notebook.
- If the solid reagent is the limiting reagent, calculate the theoretical yield based on the actual amount used, not on the amount specified in the experimental procedure.
It is important to be precise and accurate when weighing a solid reagent. Use the appropriate weighing boat or paper for the amount of solid you need to weigh, and avoid touching the reagent with your hands or the spatula as it can affect the accuracy of the measurement. Also, make sure to clean the spatula and balance scale after use to avoid contamination.
How to weigh liquid?
Weighing a liquid requires careful consideration of both the liquid and the container. Here is a more detailed explanation of the steps involved:
Determine the tare weight: The tare weight is the mass of the empty container or vessel that will be used to hold the liquid. The weight of the container needs to be known and recorded so that it can be subtracted from the total weight after the liquid is added. This can be done by weighing the empty container on the balance and recording the weight or by using the zero button on the balance to tare the weight of the container.
Use a cap or stopper: If the liquid is volatile and tends to evaporate quickly, a cap or stopper should be used to prevent any loss of the liquid during the weighing process. The cap or stopper should also be included in the tare weight.
Calculate the required volume: To weigh a specific amount of a liquid compound, you need to calculate the required volume from its density. The density of the liquid is typically given in units of g/mL or g/cm^3. You can use the formula density = mass/volume to calculate the required volume. Once you have the volume, you can transfer the liquid to the tared container.
Weigh the container with the liquid: After adding the liquid to the tared container, weigh the container with the liquid and the cap or stopper. The total weight will be the tare weight plus the weight of the liquid and the cap. Subtract the tare weight from the total weight to obtain the weight of the liquid.
Alternatives for small amounts of liquid: If the amount of liquid needed is less than 1g, it may be challenging to measure the required volume accurately. In this case, you can add the liquid drop by drop to the tared container until the desired mass is achieved. Another option is to use a micropipette to measure the liquid accurately.
In summary, weighing a liquid requires careful attention to both the liquid and the container. It is important to determine the tare weight, use a cap or stopper for volatile liquids, calculate the required volume accurately, and weigh the container with the liquid precisely.