Chapter 14 - Elements, Compounds and Mixtures
1. Who are my companions?
| Group ‘A’ | Group ‘B’ |
|---|---|
(i) Stainless steel | (a) Non-metal |
(ii) Silver | (b) Compound |
(iii) Bhajani mixture for milling | (c) Mixture |
(iv) Salt | (d) Element |
(v) Coal | (e) Alloy |
(vi) Hydrogen | (f) Metal |
Ans:
| Group ‘A’ | Group ‘B’ |
|---|---|
(i) Stainless steel | (e) Alloy |
(ii) Silver | (f) Metal |
(iii) Bhajani mixture for milling | (c) Mixture |
(iv) Salt | (b) Compound |
(v) Coal | (d) Element |
(vi) Hydrogen | (a) Non-metal |
(ii) Write the names of elements from the following symbols : Zn, Cd, Xe, Br, Ti, Cu, Fe, Si, Ir, Pt.
Zn
Ans: Zinc
Cd
Ans: Cadmium
Xe
Ans: Xenon
Br
Ans: Bromine
Ti
Ans: Titanium
Cu
Ans: Copper
Fe
Ans: Iron
Si
Ans: Silicon
Ir
Ans: Iridium
Pt
Ans: Platinum
3. What are the molecular formulae of the following compounds ?
Hydrochloric acid, sulphuric acid, sodium chloride, glucose, methane.
Ans:
Hydrochloric Acid – HCl
Sulphuric Acid – H₂SO₄
Sodium Chloride – NaCl
Glucose – C₆H₁₂O₆
Methane – CH₄
4. Give scientific reasons.
(a) Buttermilk is churned to get butter.
Ans:
Churning is one of the methods of separation. The particles of butter are all spread out in the buttermilk. By stirring, they aggregate due to centrifugal force and form one solid mass; therefore, buttermilk is churned to get butter.
(b) In chromatography, the ingredients of a mixture rise up to a limited height when water rises up to the upper end of the paper.
Ans:
Chromatography is a separation technique used to separate the different components of a liquid mixture. Separation of substances by chromatography is based on two properties of the substance:
(i) the solubility of the substance in the solvent that moves up
(ii) the ability of the substance to stick to the stationary filter paper
These properties are different for different substances and are mutually exclusive. It is the reason why all the components of the mixture rise to a limited height when the water rises to the upper end of the paper.
(c) A wet cloth is wrapped around a water storage container in summer.
Ans:
The moisture in the wet cloth evaporates during the summer season. During its evaporation, it absorbs some amount of heat from the water storage container. The water inside the container thus becomes cooler. Hence, a wet cloth is wrapped around a water storage container in summer.
5. Explain the difference.
(a) Metals and non-metals
Ans:
| Metals | Non-metals |
|---|---|
(i) Metals have luster. | (i) Non-metals do not have lustre. |
(ii) Metals are good conductors of heat and electricity. | (ii) Non-metals are not good conductors of heat and electricity. |
(iii) Normally, metals have a high density. | (iii) Normally, non-metals have less density. |
(iv) At normal temperature, metals are in their solid states except for mercury, which is in its liquid state. | (iv) At normal temperature, non-metals are either in a solid or a gaseous state, with the exception of bromine, which is in a liquid state. |
(b) Mixtures and compounds.
Ans:
| Mixtures | Compounds |
|---|---|
(i) A mixture is obtained by mixing two or more substances. | (i) A compound is made of two or more elements chemically combined in a fixed proportion. |
(ii) The constituents of a mixture retain their original properties. | (ii) The properties of a compound are entirely different from the properties of its constituents. |
(iii) A mixture can be further subdivided into simpler substances by simple physical processes. | (iii) A compound can be further divided into simpler substances by chemical means only. |
(c) Atoms and molecules.
Ans:
| Atoms | Molecules |
|---|---|
(i) An atom is the smallest particle in an element that has the properties of the element. | (i) Molecules are formed by the combination of two or more atoms. |
(ii) An atom is not stable by itself. | (ii) A molecule is usually stable enough to exit by itself. |
(iii) It is not possible to breakdown the atom further, retaining the properties of the element. | (iii) Molecules can be divided into individual atoms. e.g., a water molecule can be further divided into oxygen and hydrogen atoms. |
(d) Separation by distillation and by separating funnel.
Ans:
| Separation by distillation | Separation by separating funnel |
|---|---|
(i) For separation of solutes from the solution, the method of distillation is used. | (i) For separation of two immiscible liquids the method of separating funnel is used. |
ii) Heat is given during the separation. | (ii) Heat is not given during the process. |
6. Write answers to the following questions in your own words.
(a) How are the components of mixtures separated by simple methods ?
Ans: There are various methods to separate the mixtures some of these are filtering, sifting, picking, winnowing, combing with magnet.
(i) Filtering: To separate insoluble substances from the solution.
(ii) Shifting: Shifting is done to separate solids of various sizes.
(iii) Picking: By this method, substances that are needed /or not needed are separated out.
(iv) Winnowing: The substances which are lighter in weight and those that are unwanted are removed from this mixture
(v) Combing with Magnet: The mixture that contain iron particles is specially combed with Magnet.
(b) Which elements (metals and non-metals), compounds and mixtures do we use in our day-to-day life ?
Ans: Elements:
Metals – iron, gold, silver, copper.
Non-Metals – Carbon, oxygen, hydrogen, nitrogen.
Compounds – Sugar, salt, oil.
Mixtures – Soap, alloys like steel, brass, 22 carat gold.
(c) In everyday life, where and for what purpose do we use centrifugation?
Ans: We use centrifugation for the following purposes in our daily lives:
(i) Drying of wet clothes in the spin tub of a washing machine.
(ii) Working of roller coasters in amusement park.
(iii) Removing water from wet lettuce in salad spinner.
(iv) Making buttermilk from youhurt.
(d) Where are the methods of separation by distillation and by separating funnel used? Why ?
Ans: Distillation:
(i) Distillation is the separation method used to separate impurities or dissolved salt from the solution.
(ii) By this method the Salute and the solvent are separated.
(iii) For removing salt from seawater distillation is used.
Using Separating Funnel:
1) When two liquids in a mixture which are immiscible with each other are to be separated, the method of separating the funnel is used.
2) This method can be used for separation of mixtures of kerosene and water.
(e) Which precaution will you take while using the methods of distillation and separation by separating funnel?
Ans:
(i) In this method of distillation, the entire apparatus should be properly set up.
(ii) The distillation flask should be carefully heated.
(iii) In the separating funnel experiment care should be taken to well manipulate the stopcock.
(iv) The malfunctioning stopcock many a times releases the liquids inadvertently.