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# Different kinds of glassware are used to measure the volume of liquids and solutions: - graduated cylinder, burette, - pipette, etc. - A volumetric flask is used to prepare a known volume of a solution. # SI unit of density = $\frac{Sl unit of mass}{Sl unit of volume}$ = kg m⁻³ or g ml⁻¹ or g cm...

# Different kinds of glassware are used to measure the volume of liquids and solutions: - graduated cylinder, burette, - pipette, etc. - A volumetric flask is used to prepare a known volume of a solution. # SI unit of density = $\frac{Sl unit of mass}{Sl unit of volume}$ = kg m⁻³ or g ml⁻¹ or g cm⁻³ # Temperature is a measure of the hotness or coldness of an object. There are three common scales to measure temperature, namely: - °C (degree Celsius) - °F (degree Fahrenheit) - K (Kelvin) # The Kelvin scale is related to Celsius scale as follows: - K = C + 273.15 # Laws of Chemical Combination - The elements combine with each other and form compounds. - This process is governed by five basic laws discovered before the knowledge of molecular formulae. ## 1.4.1 Law of conservation of mass: - Antoine Lavoisier (1743-1794) is often referred to as the father of modern chemistry. - He carefully performed many experiments, namely combustion, burning of phosphorus and mercury, both in the presence of air. - Both resulted in an increase in weight. - After several experiments he found that the weight gained by the phosphorus was exactly the same as the loss of weight by the air. - He observed that, *Total mass of reactants = Total mass of products*. - This law can also be stated as *mass can neither be created nor destroyed*. ## 1.4.2 Law of Definite Proportions: - French chemist, Joseph Proust, conducted experiments on two compounds of copper carbonate. - One of the samples was of natural origin and the other one was prepared in the laboratory. - He found that the composition of copper carbonate in it was same for both the samples. - This law can also be stated as *a given compound always contains same proportion of the constituent elements by mass regardless of its source*. ## 1.4.3 Law of Multiple Proportions: - This law was proposed by John Dalton in 1803. - It has been observed that two or more elements may form more than one compound. - The Law of multiple proportions can explained by many experiments on some compounds formed by two elements, A and B. - In these compounds, the masses of element A which combine with a given mass of element B are always in the ratio of small whole numbers, for example, hydrogen combines with oxygen to form two compounds, namely water and hydrogen peroxide.