Is Matter Around Us Pure

Q. List the various types of homogeneous and heterogeneous mixtures with examples.

Q. You are given two liquids A and B. One is a compound or a pure substance and the other is a mixture (solution). How will you select the compound?

Q. When iron filings and sulphur are mixed in a particular fashion, the following observations are made.

1. No iron gets attracted to a magnet placed in the resultant matter.
2. A foul smelling gas is released when the mixture is treated with dilute sulphuric acid. Giving reasons, state whether the resultant substance is a mixture or a compound.

Q. 5 g and 10 g respectively of copper sulphate are added into two beakers each containing 100 g water. The compositions of these two mixtures are different. Are these homogeneous mixtures? Explain.

True solution

A solution, in which the particles of the solute are broken down to such a fine state that every portion of the solution has the same properties, is called a true solution. A true solution is a homogeneous mixture of two or more substances. In a true solution, the particles of the solute are broken down to a diameter of the order of 10-8 cm or less. e.g., sugar dissolved in water, iodine in ethyl alcohol (tincture).

Characteristics of True Solution

1. A true solution is always clear and transparent, i.e., light can easily pass through it without scattering. This path of light is not visible in a solution.
   
2. The particles of solute break down to almost molecular size and their diameter is of the order of 1 nm (10^-9 metre) or less.
   
3. A true solution can completely pass through filter paper as particle size of solute is far smaller than the size of pores of filter paper. Thus, the particles of the solute cannot be separated by filtration.
   
4. A true solution is homogeneous in nature.
   
5. In a true solution, the particles of solute do not settle down, provided temperature is constant. Thus, the true solution is stable in nature.
   
6. From a true solution, the solute can easily be recovered by evaporation or crystalliasation.

Solute. The substance(s) present in smaller proportion in a solution is called solute.

Solvent. The substance present in larger proportion in a solution is called solvent. If a homogeneous mixture or a solution is formed by dissolving 2 g salt in 100 g water, then salt is the solute and wateris the solvent.

Solubility. The maximum a mount of the solid that can be dissolved in a given amount of the solvent (water) is termed its solubility at that temperature.

Differentiate between a saturated solution and an unsaturated solution

Saturated solution. A solution in which no more of the solid (solute) can be dissolved at a given temperature is called a saturated solution.

Unsaturated solution. A solution in which more of the solid can be dissolved at the given temperature is called an unsaturated- solution.

Test whether a given solution is saturated or not.

If to a given solution, more salt is added and it dissolves, then it is unsaturated. If the salt added settles down; it is saturated.

Q. How will you prepare a saturated solution of copper sulphate in water at 50ºC? What will happen if this solution is allowed to cool?

Q. Given a solution of substance A, how will you test whether it is saturated or unsaturated with respect to A at the prevailing temperature? What is observed when a hot saturated solution of a substance is allowed to cool?