Molar concentration is a size which shows how many moles of a substance are in the 1st liter of solution. For example, it is known that in liter of solution there are exactly 58.5 grams of table salt – chloride sodium. As molar this substance just also makes 58.5 g/mol, one may say, that in this case you have one-molar solution of salt. (Or, in the form of record, 1M solution).
It is required to you
- - table of solubility of substances.
Instruction
1. The solution of this task depends on specific conditions. If you know the exact mass of substance and exact volume of solution, then the decision very simple. For example, 15 grams of chloride barium contain in 400 milliliters of solution. What its molar concentration?
2. Begin with the fact that remember an exact formula of this salt: BaCl2. According to Mendeleyev's table, determine atomic masses of the elements which are its part. And, taking into account index 2 at chlorine, receive molecular weight: 137 + 71 = 208. Therefore, molar mass of chloride of barium of 208 g/mol.
3. And under the terms of a task, solution contains 15 grams of this substance. How many it in moths? Having divided 15 into 208, receive: about 0.072 asking.
4. Now you should consider that solution volume on 1 liter, and only 0.4. Having divided 0.072 on 0.4, receive the answer: 0.18. That is, you have approximately 0.18-molar solution of chloride barium.
5. Let's a little complicate the solution of a task. Let's assume that you would begin to dissolve in 100 milliliters of water at the room temperature already mentioned, well familiar to you, table salt – chloride sodium. You added it in the small portions, carefully stirring and waiting for full dissolution. And there came the moment when the next small portion was not dissolved up to the end, despite intensive hashing. It is required to define what molar concentration of the received solution.
6. First of all, you should find tables of solubility of substances. They are in the majority of chemical reference books, it is also possible to find for these data on the Internet. You without effort define that at the room temperature a saturation limit (that is, a solubility limit) chloride sodium – 31.6 grams / 100 water gram.
7. Under the terms of a task, you dissolved salt in 100 milliliters of water, but its density is almost equal to 1. So we draw a conclusion: the received solution contains about 31.6 grams of chloride sodium. The small not dissolved surplus and also some change of volume at dissolution of salt can be neglected, the error will be small.
8. Respectively, in 1 liter of solution would contain in 10 times more of salt – 316 grams. Considering that the molar mass of chloride sodium as it was specified in the beginning, is 58.5 g/mol, you will easily find the answer: 316/58.5 = 5.4-molar solution.