How to calculate a caption

How to calculate a caption

Very often in the chemical analysis instead of mass concentration the caption of solution which shows the content of any substance in one milliliter of solution is used. For record of a caption the symbol in the form of capital Latin letter t is accepted. And unit of its measurement is g/ml.

It is required to you

  • - paper;
  • - handle;
  • - calculator.


1. For finding of a caption on the dissolved substance (simple caption) use a formula: T = m/V where T is a caption; m – the mass of the substance dissolved in liquid, V – solution volume in milliliters or cubic centimeters.

2. Besides, you will be able to calculate a caption on the defined substance. This size is called still a conditional caption. For this purpose the formula is required: T (a/b) = mb/Va, where T (a/b) - substance a solution caption on substance b; mb is the mass of substance b (in grams) which interacts with this solution; Va is substance a solution volume (in milliliters).

3. For example, it is necessary to find a caption of the solution of phosphoric acid weighing 18 g received at dissolution of H3PO4 in 282 milliliters of water. Density of solution is equal to 1.031 g/ml. For a start find weight, the prepared solution, considering at the same time that 282 ml of water will be equal to 282 g: 28+282 = 300 (g). Then, count its volume: 300/1.031 = In 291 (ml). Now substitute in a formula and find a caption: 18/291 = 0.0619 (g/ml).

4. Besides above the described methods, you can also calculate a caption, knowing the equivalent weight and normality (equivalent concentration). T = Sn*Mekv/1000 where T is a caption, Sn – normality, Mekv – equivalent weight.

5. Quite often you will face tasks in which it will be required to express a caption of one substance through another. For example, the condition is given: 25 ml of solution of sodium hydroxide were spent for titration of 20 ml of solution of hydrochloric acid with a caption of 0.0035 g/ml. It is necessary to calculate NaOH caption on HCl.

6. At first write down the reaction equation: NaOH + HCl = NaCl + H2O. Then calculate an alkali solution caption on a formula: T (NaOH) = T(HCl) * V (HCl) * M (NaOH)/M (HCl) * V (NaOH). Having substituted digital values, receive a caption of sodium hydroxide of equal 0.0031 g/ml. It was necessary to calculate value, necessary for the solution of a task: T (NaOH/HCl) = T(NaOH) * Mekv (HCl) / Mekv (NaOH) of =0.0028 g/ml

Author: «MirrorInfo» Dream Team