How to Calculate the Concentration of a Solution

2024 Author: Samantha Chapman | [email protected]. Last modified: 2023-12-17 09:13

A freshwater aquarium can become very salty over time. Certain fish foods and tap water can add surprising amounts of salt to the aquarium in a very short period of time. During the hot season a lot of water evaporates, but the dissolved calcium and salt remain in the tank as much as the chlorides. Although this test reveals the presence of sodium chloride, the precipitates may also include calcium chloride. Check the sodium chloride concentration with this method. Obviously this technique can also be used with plain water in which you suspect there is salt. Don't be discouraged with chemistry; doing this test is quite simple and inexpensive.

Steps

Step 1. Measure the volume of the water sample precisely

In this article we use the International System (S. I.) and milliliters (mL).

Step 2. Use an additive that will produce insoluble sodium chloride

In this case, AgN03 (silver nitrate) is used. Measure the silver nitrate from a burette or a small syringe and add it to the water sample until the solution stops and becomes cloudy. It is important to know exactly the amount of silver nitrate you have added, in this way you can calculate the amount of salt.

Step 3. When the silver nitrate no longer cloud the solution, record the number of mL you used

You have to dose the nitrate very slowly and observe the solution carefully. For example, suppose 3 mL of AgNO3 is served in 3 mL of water sample to make it clear.

Step 4. The reaction is:

"Ag +" + "Cl-" - AgCl (s) "(s) means solid, ie the precipitate of the 3 mL solution.

Step 5. Determine the molar mass of AgNO3 that caused the precipitate

To do this, use the periodic table and add the atomic weights of silver, nitrogen and oxygen (multiply that of oxygen by 3 because the molecules are 3).

• Step 6.

  

  

  Step 7. The molar ratio is = 0.017660886 g / mole

  Don't round this number, not yet.

  

  Step 8. Multiply the molar ratio by the molar mass of sodium chloride, which is the atomic weight of sodium plus that of chlorine

• Step 9.

  Step 10. The approximate result is 1.03g of NaCl in 3 mL of water sample

  This means too much NaCl. Change the aquarium water 10% at a time in 10 days.

  Advice

  • Use only clear plastic or glass.
  • Here is a video: [1]
  • Ag + 2 HNO3 → AgNO3 + NO2 + H2O

  Warnings

  • Keep the AgNO3 solution in a dark, sealed bottle. It is sensitive to light.
  • If you want your silver back then: Cu (s) + 2 AgNO3 (aq) → Cu (NO3) 2 + 2 Ag (s) Remember that (s) means solid.
  • Be careful when working with strong acids. Work under an extractor hood or outdoors.
  • Wear protective gloves and goggles.