9. How will you account for the following: ] i) Fresh air cannot be regarded as a pure substance. ii) Sodium chloride contains two elements, but it is still considered a pure substance. iii) A mixture of sugar & water is homogeneous while that of oil & water is heterogeneous.
Answers
Air is mixture of many gases, like, oxygen (O2), Nitrogen (N2), Argon (Ar), Carbon Dioxide (CO2) and many other gases in traces like hydrocarbon etc. Air is mixture of gases so it is not regarded as pure substance, it is mixture of many pure substances.
Sodium Chloride is pure substance because it is having uniform property and constant chemical of sodium & chloride (Na & Cl). Sodium and Chloride are two different elements but when they combine and form NaCl, they will be having constant Chemical property and composition i.e. Salt (NaCl) hence NaCl is pure substance.
Homogeneous mixture is mixture which is having same proportion of its components and have single phase. like when you Dissolve sugar in water, sugar is uniformly distributed in water and make it single phase, hence mixture of sugar and water is homogeneous mixture.
where as, heterogeneous mixture is nothing but, having non uniform composition and have two or more than two phases, so oil and water will make two phases and distribution of oil in water is non uniform, hence oil and water mixture is called as heterogeneous mixture.
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