It serves as the negative control
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Water is often used as a control sample because it is a neutral substance that does not interfere with the experiment. By comparing the results from the experimental samples to the control sample of water, researchers can more accurately determine the effects of the variables being tested. Additionally, water is readily available, inexpensive, and easily controlled for consistency.
A sample bottle is used to hold small quantities of liquid for analysis or testing. It allows for convenient and safe storage and transportation of samples for various purposes such as laboratory testing, quality control, or research.
Extracting with 25ml of water is often used in sample preparation to dissolve, dilute, or extract compounds for analysis. It is a common method to dissolve water-soluble components from a sample and can be used to extract analytes of interest for further testing or analysis. The volume of water used can be adjusted based on the solubility and concentration of the compounds being targeted.
Lime water is used during the reaction of the acid sample with marble chips to test for the presence of carbon dioxide. If carbon dioxide is produced during the reaction, it will react with the lime water to form a white precipitate of calcium carbonate, confirming the presence of carbon dioxide in the acid sample.
In order to determine the mass of the water sample, you would need to know the density of water. The density of water is approximately 1 g/cm3. Therefore, the mass of a 20 cm3 sample of water would be 20 grams (20 cm3 * 1 g/cm3 = 20 grams).
A control tube is used in experiments to provide a baseline for comparisons. It is used to ensure that any changes in the experiment can be attributed to the variables being tested, rather than external factors.