Solutions Online Test 10th Science Lesson 9 Questions in English

The substances present in a mixture may exist in one or more physical state. For example, when we burn wood, the smoke released is a mixture of solid carbon and gases like CO2, CO, etc.

The kind of homogenous mixtures are termed as “solutions”.

A solution is a homogeneous mixture of two or more substances. In a solution the component which is present in lesser amount (by weight), is called solute and the component, which is present in a larger amount (by weight) is called solvent.

The solute gets distributed uniformly throughout the solvent and thus forming the mixture homogeneous. So, the solvent acts as a dissolving medium in a solution.

The process of uniform distribution of solute into solvent is called dissolution.

A solution must at least be consisting of two components (a solute and a solvent). Such solutions which are made of one solute and one solvent (two components) are called binary solutions.

A solution may contain more than two components. For example if salt and sugar are added to water, both dissolve in water forming a solution. Here two solutes are dissolved in one solvent. Such kinds of solutions which contain three components are called ternary solutions.

In binary solutions, both the solvent and solute may exist in any of these physical states. But the solvent constitutes the major part of the solution. Its physical state is the primary factor which determines the characteristics of the solution.

Most of the substances are soluble in water. That is why, water is called as ‘Universal solvent”.

On the basis of type of solvent solutions are classified into two types. They are aqueous solutions and non-aqueous solutions.

The solution in which water acts as a solvent is called aqueous solution. E.g. Common salt in water, Sugar in water and Copper sulphate in water.

The solution in which any liquid other than water acts as a solvent is called non-aqueous solution. Solvent other than water is referred to as non-aqueous solvent.

Generally alcohols, benzene, ethers, carbon disulphide, acetone, etc., are used as non-aqueous solvents.

Examples for non-aqueous solutions: Sulphur dissolved in carbon disulphide, Iodine dissolved in carbon tetrachloride.

Based on the amount of solute in the given amount of solvent, solutions are classified into the following types as, saturated solution, unsaturated solution and Super saturated solution.

Saturated solution: A solution in which no more solute can be dissolved in a definite amount of the solvent at a given temperature is called saturated solution. e.g. 36 g of sodium chloride in 100 g of water at 25°C forms saturated solution.

Unsaturated solution: Unsaturated solution is one that contains less solute than that of the saturated solution at a given temperature. e.g. 10 g or 20 g or 30 g of Sodium chloride in 100 g of water at 25°C forms an unsaturated solution.

Super saturated solution is one that contains more solute than the saturated solution at a given temperature. e.g. 40 g of sodium chloride in 100 g of water at 25°C forms super saturated solution.

Super saturated solution state can be achieved by altering any other conditions liken temperature, pressure. Super saturated solutions are unstable, and the solute is reappearing as crystals when the solution is disturbed.

Concentrated and dilute solutions: It is another kind of classification of unsaturated solutions. It expresses the relative concentration of two solutions with respect to their solutes present in the given amount of the solvent.

When we compare two solutions having same solute and solvent the one which contains higher amount of solute per the given amount of solvent is said to be ‘concentrated solution’.

Differentiating solutions as dilute and concentrated is a qualitative representation. It does not imply the quantity of the solute. This difference is observed by means of some physical characteristics such as color, density, etc.

The extent of dissolution of a solute in a solvent can be better explained by its solubility. Solubility is a measure of how much of a solute can be dissolved in a specified amount of a solvent.

Solubility is defined as the number of grams of a solute that can be dissolved in 100 g of a solvent to form its saturated solution at a given temperature and pressure.

Solubility’s of some common substances in water at 25°C

There are three main factors which govern the solubility of a solute. They are Nature of the solute and solvent, Temperature and Pressure.

Nature of the solute and solvent: The nature of the solute and solvent plays an important role in solubility. Although water dissolves an enormous variety of substances both ionic and covalent, it does not dissolve everything.

Non-polar compounds are soluble in non-polar solvents. For example, Fat dissolved in ether. But non-polar compounds do not dissolve in polar solvents; polar compounds do not dissolve in non-polar solvents.

Generally solubility of a solid solute in a liquid solvent increases with increase in temperature. For example, a greater amount of sugar will dissolve in warm water than in cold water.

The solubility of the endothermic process increases with increase in temperature. Exothermic process solubility decreases with increase in temperature.

The Solubility of gases in liquid decrease with increase in temperature. Generally, water contains dissolved oxygen. If water is heated the solubility of oxygen in water decreases so oxygen escapes in the form of bubbles.

Aquatic animals live more in cold regions because more amount of dissolved oxygen is present in the water of cold regions. This shows that the solubility of oxygen in water is more at low temperatures.

Effect of pressure is observed only in the case of solubility of a gas in a liquid. If the pressure is increased the solubility of a gas in liquid increases.

The common examples for solubility of gases in liquids are carbonated beverages, i.e. Soft drinks, household cleaners containing aqueous solution of ammonia, formalin aqueous solution of formaldehyde, etc.

The effect of pressure on the solubility of a gas in liquid is given by Henry’s law. It states that, the solubility of a gas in a liquid is directly proportional to the pressure of the gas over the solution at a definite temperature.

Most of the chemical reactions take place in solutions form. So it is essential to quantify the solute in solvent to study the reactions. To quantify the solute in a solution, we can use the term “concentration”.

Concentration of a solution may be defined as the amount of solute present in a given amount of solution or solvent.

Quantitatively, concentration of a solution may be expressed in different methods. But here we shall discuss percentage by mass (% mass) and percentage by volume (% volume).

Mass percentage of a solution is defined as the percentage by mass of the solute present in the solution. It is mostly used when solute is solid and solvent is liquid. Mass Percentage = (Mass of the solute / Mass of the solution) * 100

Usually, mass percentage is expressed as w/w (weight / weight); mass percentage is independent of temperature.

Volume of the ethanol = 30 ml and Volume of the water = 70 ml Volume percentage = (Volume of the solute / Volume of the solution)* 100 = Volume of the solute / (Volume of the solute + Volume of the solvent) * 100 Volume percentage = 30 / (30+ 70) * 100 = 30%

Mass of the solute (NaOH) = 20 g and Mass of the solvent H2O = 100 g Mass percentage of the solute = Mass percentage of solute / (Mass of the solute +Mass of the Solvent)*100 = 20 * 100 / (20+100) = 16.67 % Mass percentage of solvent = 100 – (Mass percentage of the solute) = 100- 16.67 = 83.33%

Usually volume percentage is expressed as v/v (volume / volume). It is used when both the solute and solvent are liquids. Volume percentage decreases with increases in temperature, because of expansion of liquid.

In the commercial products that we come across in our daily life such as a solution of syrups, mouth wash, antiseptic solution, household disinfectants etc., the concentration of the ingredients is expressed as v/v. Similarly, in ointments, antacid, soaps etc., the concentration of solutions are expressed as w/w.

When ionic substances are dissolved in water to make their saturated aqueous solution, their ions attract water molecules which then attached chemically in certain ratio. This process is called hydration.

The ionic substances crystallize out from their saturated aqueous solution with a definite number of molecules of water. The number of water molecules found in the crystalline substance is called water of crystallization. Such salts are called hydrated salts.

On heating these hydrated crystalline salts they lose their water of crystallization and become amorphous or lose their color (if they are colored).

The number of water molecules in blue vitriol is five. So its water of crystallization is 5. When blue colored copper sulphate crystals are gently heated, it loses its five water molecules and becomes colorless anhydrous copper sulphate.

Magnesium sulphate hepta-hydrate MgSO4.7H2O (Epsom salt) water of crystallization is 7. When magnesium sulphate hepta-hydrate crystals are gently heated, it loses seven water molecules and becomes anhydrous magnesium sulphate.

Certain substances when exposed to the atmospheric air at ordinary temperature absorb moisture without changing their physical state. Such substances are called hygroscopic substances and this property is called hygroscopy.

Hygroscopic substances are used as drying agents. Example: Con Sulphuric acid (H2SO4), Phosphorus Pentoxide (P2O5), Quick lime (CaO) and Silica gel (SiO2).

Deliquescent substances lose their crystalline shape and ultimately dissolve in the absorbed water forming a saturated solution.

Deliquescence is at its maximum when the temperature is low and the atmosphere is humid.

Examples for deliquescence are Caustic soda (NaOH), Caustic potash (KOH) and Ferric chloride (FeCl3).