A sample of hard water contains 0.005 mole of CaCl2 per litre. What is the minimum concentration

A sample of hard water contains 0.005 mole of CaCl2 per...

Key Concepts

Water Hardness and Ion Removal

Water hardness refers to the presence of certain metal cations in water, which can cause scaling and interfere with cleaning processes. In water treatment, precipitation reactions are often employed to remove hardness-causing ions by adding chemicals that supply counter-ions, leading to the formation of insoluble compounds that can be separated from the water.

Ionic Dissociation and Stoichiometry

When an ionic compound dissolves, it dissociates into its constituent ions in fixed ratios as dictated by its chemical formula. Understanding the stoichiometry of this dissociation is crucial when calculating the resulting concentrations of ions that may participate in equilibrium or precipitation reactions.

Solubility Product (Ksp)

The solubility product is a constant that represents the product of the concentrations of the ions produced when a sparingly soluble salt dissolves, each raised to the power of its coefficient in the dissolution equation. It is used to predict whether a precipitate will form under given ionic concentrations in solution.

Precipitation Equilibrium

Precipitation equilibrium describes the state in which a dissolved salt and its solid phase coexist when the product of the ion concentrations equals the salt’s Ksp. When the ion?product in a solution exceeds the Ksp, the excess ions combine to form a precipitate, thereby reducing the concentration of free ions.

Transcript

00:01 Hi student, here we are given a solubility product of calcium fluoride, caf2, as 3 .2 multiplied by 10 raised to minus 11 molar cube and we have to find the solubility in saturated solution.

00:12 So actually we have to find a relationship between ksp, solubility product and solubility s.

00:19 What exactly is a difference between both? solubility product is a constant value.

00:24 It won't change at a particular temperature.

00:27 It is defined at a particular temperature.

00:28 It can only change if temperature changes and it's not affected by the conservation changes of the cf2 taken.

00:35 The cf2 electrolide taken will be having an ionic equilibrium with its constituent ions as cf2 in equilibrium with 1 mole of ca2 plus and 2 moles of f2 minus.

00:47 So this is a 1 -neast 2 ratio salt.

00:49 Cf2 is 1 -neast -2 ratio since this stociometry is the maintained 1 in balanced equation.

00:56 All right.

00:57 So ksp would be given by the equation, its product, it's a maximum possible product of ionic concentrations with the concentration terms raised to the power that is equal to the stociometric coefficient of that particular ion in the balanced equation of ionic equilibrium.

01:17 To be more precise, the product of concentrations, that is 3a2 plus multiplied by f minus concentration, but the power of that concentration term or the term would be raised to the power that is equal to the stoichiometric coefficient of that particular ion.

01:33 In c2c, it is one, but needless to say, it's already one itself, and f minus it's to be said that is square because here we have a coefficient of two here.

01:46 So, in this equation, we have this value to be, this constant value that is given, and at a particular temperature, this won't change even if we change the concentration of cf2.

01:58 Solubility is nothing but it is the number of moles of this electrolyte soluble or the solubility per mole, let's we can say in that way.

02:09 And how many moles of salt or electrolyte would be soluble? that is the measure of this term solubility.

02:16 And let's say in this ratio, one needs to two ratio, this ratio would be corresponding to the solubility ratio also.

02:22 That is 1 molar caf2 if in equilibrium it will give s solubility or solubility of ca2 plus to be s and solubility of f minus to be 2s.

02:37 Since the coefficient is 1 is 2, all right.

02:41 So substituting this solubility values because we need to find a relationship between ksp and s as the equation such as we need to find solubility.

02:50 We are already given ksp.

02:52 So we have to find a relation.

02:54 We can directly substitute s multiplied by f minus concentration is analogous to that of solubility values that is 2 s square we can equate solubility with that of concentration because it itself says the number of moles that is soluble or the solubility is per mole all right so s multiplied by 4 s square that is 4s cube only and this 4s cube is equal to ksp now we have got a relationship between ksp and solubility.

03:28 Using this we can simply get the value of solubility of cf2 in saturated solution...

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