Solutions-Class 7-Science-Chapter-14-Elements, Compounds and Mixtures-Maharashtra Board

1. Zn- Zinc

2. Cd- Cadmium

3. Xe- Xenon

4. Br- Barium

5. Ti- Titanium

6. Cu- Copper

7. Fe- Iron

8. Si- Silicon

9. Ir- Iridium

10. Pt- Platinum

• Butter milk has two components- water and fat/cream.
• Churning helps in the separation of these two components.
• By stirring they aggregate due to centrifugal force and form solid lump.
• The fat/cream collects on the top as a result of churning while the remaining part is left behind as liquid.
• To separate butter, the buttermilk is therefore churned.

Chromatography is a separation technique used to separate the different components in a liquid mixture. Separation of substances by chromatography is based on two properties of the substance:

1. Solubility of the substance in the solvent that moves up
2. Ability of the substance to stick to the stationary filter paper

These properties are different for different substances and are mutuall opposite to each other. Since water is a solvent, it rises rapidly across the chromatography filter paper. But the solutes will not rise with that speed. Therefore, the ingredients of a mixture rise up to a limited height when water rises up to the upper end of the paper.

A wet cloth is wrapped around water containers in summers to keep the container and the water inside it cools. The water present in the cloth evaporates. During evaporation it absorbs some amount of heat from the water storage container. The water inside the container thus becomes cooler. Thus keeping the container and water cool a wet cloth is wrapped around it.

The components of mixtures are separated by simple methods like:
Distillation: When mixtures consist of two or more pure liquids than distillation is used. Here the components of a liquid mixture are vaporized, condensed and then isolated. The mixture is heated and the component which is volatile vaporizes first. The vapour moves through a condenser and is collected in a liquid state. This helps in making potable water from sea water

Separating funnels: Separation using separating funnels is used in case of immiscible liquids. It is based on the difference in the density of the two liquids. It can be used in separation of oil from water etc, two different types of immiscible oils etc.

Chromatography: It can be used to separate the coloured components of a mixture on the basis of the difference in the speeds of the components on chromatograph paper, when dissolved in the same solvent. The component which moves slowly (i.e., the less-soluble component) appears as a spot on the lower side of the paper. The component which moves faster (i.e., the more-soluble component) appears as a dot on the higher side of the paper.

Centrifugation: Centrifugation is the process where a mixture is separated through spinning. It is used to separate skim milk from whole milk, water from your clothes, and blood cells from the blood plasma. 

Magnetic Separation: If there is adulteration of semolina with iron, the magnet is combed through it for removing these iron particles. The mixture that contains iron particles is specially combed with a magnet,

Sifting : Sifting is done to separate solids of various sizes. The larger particles and
the smaller particles can be separated by sifting.

Picking and sorting : By this method, a substances that are needed/or not needed
are separated out
 

Mixtures we use in our daily life are- lemon and water, sugar and milk, salt and water, cereal and milk, cement, Soap,alloys like steel,brass etc.
Compounds - salt (NaCl), sugar (C₁₂H₂₂O₁₁), baking powder (NaHCO₃), Oil, etc.
Elements - Metals-aluminium, copper, iron, silver, gold etc. Non-metals –Carbon, hydrogen, oxygen etc.
 

By using method of centrifugation the particles of smaller size are separated due to centrifugal force.

We use centrifugation for the following purposes in our daily lives:

• We use stirrer for making buttermilk from yoghurt.
• Drying of wet clothes in the spin tub of a washing machine
• Separation of blood components in medical science
• Working of roller coasters in amusement park
• Removing water from wet lettuce in salad spinner

1) Distillation : Distillation is the separation method used to separate impurities
or dissolved salts from the solution. By this method, the solute and the solvent are separated.
For removing salt from sea water, distillation method is used. This helps in making potable water from sea water.
2) Using separating funnel : Separation using separating funnels is used in case of immiscible liquids. It is based on the difference in the density of the two liquids. It can be used in separation of oil from water etc. two different types of immiscible oils etc. This method can be used for separation of mixture of kerosene and water.

Precautions required during distillation:

• The apparatus should be set in a proper manner with all the components fitted well.
• Never heat the system that is totally closed from the outside atmosphere to prevent explosion.
• Add boiling chips to reduce bumping (rapid boiling causing the liquid to expel out of the container).
• Control the rate of heating so not to overheat to avoid bumping.

Precautions required while using separating funnel for separation:

• The funnel should be tightly fixed to the stand in an erect position.
• The liquid in the funnel should be left undisturbed to allow it to separate.
• The stopper should be removed carefully without disturbing the setup.