Chapter 05: Separation of Substances

    I. Multiple Choice Questions (MCQs).
    Q.1. A pure substance consists of only one type of
    a) properties
    b) particles
    c) materials
    d) none of these
    Answer b) particles
    Q.2. A mixture in which its constituents are not distributed uniformly, is called
    a) homogeneous
    b) heterogeneous
    c) supernatant
    d) saturated
    Answer: (b) heterogeneous
    Q.3. When the visible unwanted particles are removed by hand, the process is called
    a) handpicking
    b) winnowing
    c) sieving
    d) threshing
    Answer: (a) handpicking
    Q.4. A single machine, by which both harvesting and threshing are carried out, is called
    a) harvester
    b) thresher
    c) combine
    d) none of these
    Answer: (c) combine
    Q.5. During the process of sedimentation, the particles which settle down are known as
    a) supernatant
    b) sediment
    c) residue
    d) filtrate
    Answer: (b) sediment

    II. Fill in the blanks by selecting appropriate words from the given list :
    List : Sieving, evaporation, homogeneous, proportions, electromagnet
    Q.1. A mixture contains two or more different substances mixed together in any _______________.
    Q.2. All solutions are _____________ mixtures.
    Q.3. Salt is obtained from sea water by _________________.
    Q.4. A temporary but very powerful magnet which attracts iron filings when electric current is passed through it, is called the _____________.
    Q.5. _____________ cannot be used when the particles of the components of a mixture, are of the same size.

    Ans: (1) proportions
    (2) homogeneous
    (3) evaporation
    (4) electromagnet
    (5) Sieving
    III. Match the items of Column A with those of Column B.

    Ans. 1-(c ), 2-(d), 3-(a), 4-(e), 5-(b)

    III. Write ‘T’ for the true and ‘F’ for the false statements.
    Q.1. Steel is a homogeneous mixture of iron and carbon, formed on mixing them in
    their molten states.
    Q.2. The different substances that are present in a mixture are called its materials.
    Q.3. Most of the substances, which are found in nature, contain some harmful or
    unwanted substances.
    Q.4. Sieving can be used when the particles of the components of a mixture are of the
    same size.
    Q.5. The process of separation of the clear liquid layer without disturbing the settled
    solid (sediment) is called decantation.

    Answer: 1- T, 2-F, 3-F, 4-F, 5-T

    V. Very Short Answer Questions.

    Q.1. Define pure substance.
    Answer: A substance consists of only one type of particles is known as pure substance.

    Q.2. What do you mean by mixture?
    Answer: A mixture contains two or more different substances mixed together in any proportion.

    Q.3. Define threshing.

    Answer: The process of separating the grains from the stalks of plants is known as threshing.

    Q.4. When is process of winnowing used for separation of a mixture?

    Answer: Winnowing is used for separating the components of a mixture, when they are nearly of the same size and the particles cannot be distinguished easily.

    4. On what basis is process of sieving used for separation of a mixture?
    Answer: If the components of a mixture are of different sizes, they can be separated by sieving.

    VI. Short Answer Questions.

    Q.1. What do you mean by sedimentation and decantation?

    Answer: The process of separating insoluble solids suspended in a liquid by allowing them to settle down is known as sedimentation.
    The process of pouring out the clear liquid without disturbing the sediment is known as decantation.

    Q.2. What do you mean by magnetic separation? Name a mixture in which this method is used from separation.

    Answer: The separation of magnetic materials from nonmagnetic materials, using a magnet is known as magnetic separation. Magnetic separation method is used to separate iron filings from a mixture of scrap.
    Q.3. Write three characteristic properties of a mixture which are useful while separating its components. Explain with proper examples. Ans:

    Q.4. Why is it necessary to separate the constituents of a mixture? Discuss with examples.

    Answer: Most of the substances, which are found in nature, contain some harmful or unwanted substances. These must be removed before using them. Others may contain a mixture of useful substances which need to be separated. For example the harmful constituents present in river water are removed by various processes before supplying it to our homes as drinking water.

    Q.5. What do you mean by evaporation and condensation? Describe a mixture in which these methods are used for separating its constituents.
    Answer: When a liquid changes into gaseous state on gentle heating, such that the liquid does not boil, the process is called evaporation.
    The process of conversion of water vapour into its liquid form is called condensation. Evaporation is used for separating salt from sea water. Sea water contains a mixture of salts. It is allowed to stand in shallow pits for a few days. Water evaporates and changes into vapour by the heat of the sun and the salt is left behind.

    VII. Long Answer Questions.
    Q.1. What do you mean by filtration? In which case this method is used? Describe an experiment in which the process of filtration is used to separate the constituents of a mixture.

    Answer: Filtration is the process of separation of insoluble solid constituents of a mixture, from a liquid by passing through a suitable porous material. Filtration used to separate insoluble solid components from a liquid. Filtration can be used to obtain clear water from muddy water.

    Materials Required : Muddy water, beaker, funnel, glass rod, filter paper and stand Procedure : Set up the funnel in the stand and keep beaker below as shown in the figure.
    Fold the filter paper to make a quadrant. Open the quadrant by keeping three layers on one side and one layer on the other side. Place the paper cone in the funnel. Now pour muddy water into the funnel with the help of a glass rod. Collect the filtrate in a beaker. Open the filter paper cone to observe the contents.

    The beaker below the funnel contains clear water without any mud particles. All the mud particles are retained on the filter paper cone.

    Q.2. What is distillation? In which kind of mixture this method of separation is used? How can you separate immiscible liquids by using a separating funnel?

    Answer: The process of separation of a liquid, from a soluble salt solution, by the evaporation of liquid and recondensation of its vapour in another vessel, is called distillation.
    Oil and water are two liquids which are not miscible with each other. A mixture of oil and water can be separated by using separating funnel. It is a device having a stopcock at its bottom. The mixture is taken in this funnel. Oil being lighter forms the upper layers. Water being denser forms the lower layers. When the stopcock opened, the layer flows out leaving the oil layer behind.

    Q.3. On which condition are the sedimentation and decantation methods used to separate a mixture? Explain the methods briefly.
    Answer: Sedimentation and decantation methods are used to separate insoluble solids from liquids. It is based on the difference in weights of different components.
    In a beaker take a mixture of sand and water. Allow it to stand undisturbed for some time. You will observe that the sand particles have settled down at the bottom of the beaker and a layer of clear water is formed above it. Slowly pour this upper layer into another beaker taking care that the sediment of sand is not disturbed.

    Q.4. How will you obtain clear water from the muddy water, if you are provided with two glass tumblers and no other apparatus?
    Answer:

    i. Take muddy water in 1st tumbler
    ii. Wait and wait and wait until the mud in the water settles down at the bottom of the tumbler
    iii. Now you should see mud collected (or sedimentated) the bottom of the tumbler iv. CAREFULLY pour the translucent water (it still has some mud) into 2nd tumbler
    v. Now wait until the mud present in that water settles down.
    vi. You will find much more transparent solution as compared to the transparency of the muddy water.

    In this way we can obtain the clear water from muddy water.

    Leave a Reply

    Your email address will not be published. Required fields are marked *