Tag: crystallisation

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Multiple choice chemistry changes around us crystallisation process of separating components of a mixture physical changes

One of most common solvent used for crystallization is:

  1. syrup

  2. normal saline

  3. water

  4. sulphuric acid
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

One of the most common solvents is water. It is also called as a universal solvent.

Crystallization is the process of formation of crystals. Since water can be easily added or removed from the system. It is the most common for eg. ${ CuSO } _{ 4 }.5{ H } _{ 2 }O$
                                     ${ Fe } _{ 2 }{ O } _{ 3 }.n{ H } _{ 2 }O$

Multiple choice chemistry changes around us crystallisation process of separating components of a mixture physical changes

The process of obtaining salt by evaporation of seawater is known as :

  1. crystallisation

  2. sedimentation

  3. galvanization

  4. amalgamation
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

It is known as crystallization - because salt is obtained in crystal form.

Sedimentation is depositing solid as sediment
Galvanization - is the process of protecting iron/metal by a coating of zinc.
Amalgamation - is the formation of amalgam (an alloy of mercury with another metal).

Multiple choice chemistry changes around us crystallisation process of separating components of a mixture physical changes

Crystals are formed by ions, atoms, and molecules having an internal pattern that is ___________ and ___________.

  1. irregular, non-repeating

  2. regular, repeating

  3. regular, non-repeating

  4. none of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In crystalline solids, the atoms, ions or molecules are arranged in an ordered and symmetrical pattern that is repeated over the entire crystal. The smallest repeating structure of a solid is called a unit cell, which is periodically repeated in three dimensions on a lattice.

Multiple choice chemistry changes around us crystallisation process of separating components of a mixture physical changes

Which of the following is the most common solvent used for crystallization?

  1. Organic solvent benzene

  2. Plain water

  3. A salt solution of water

  4. Dilute solution of sulphuric acid
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The most common solvent used in crystallization is water, it does not dissolve the substance to be purified at room temperature, but it dissolves it well at solvent's boiling point, and dissolves soluble impurities well at room temperature.
Water is capable of dissolving a variety of different substances than any other liquid and is called the universal solvent.

Multiple choice chemistry changes around us crystallisation process of separating components of a mixture physical changes

Solvent dissolve large amount of solute at________

  1. room temperature

  2. boiling temperature

  3. freezing temperature

  4. less than room temperature but more than freezing temperature
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The solvent dissolves a large amount of solute at boiling temperature, i.e an increase in temperature increases the solubility of the solute. As the temperature increases, the particles of the solid move faster which increases the chances that they will interact more with the solvent molecules. As the temperature increases, the amount of solute that can be dissolved in a solvent increases generally is high at their individual boiling points.

Multiple choice chemistry changes around us crystallisation process of separating components of a mixture physical changes

Vacuum desiccator is used  _____ 

  1. for drying crystals

  2. for purifying crystals

  3. for separation of crystals

  4. for the process of crystallisation
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Desiccators are an economical and reliable way to assure dry, dust-free storage and organization of humidity sensitive products valuable reagents in crystalline form. Proper storage conditions can be optimized by selecting a desiccator size, shape and control mechanism best suited for the application.
The lower compartment of the desiccator contains lumps of silica gel, anhydrous calcium chloride to absorb water vapor. The substance needing the desiccation is put in the upper compartment, on a glazed perforated ceramic plate. The ground glass rim of the desiccator lid must be greased with a thin layer of vacuum grease. 

Multiple choice chemistry changes around us crystallisation process of separating components of a mixture physical changes

Phenolphthalein is a synthetic indicator and its color in acidic and basic solutions, respectively are: 

  1. red and blue

  2. blue and red

  3. pink and colorless

  4. colorless and pink
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Phenolphthalein [3,3-Bis (4- hydroxyphenyl)- 2 benzofuran- 1-one] is often used as an indicator in acid-base titrations. It turns colourless in acidic solutions and pink in basic solutions.

Multiple choice chemistry changes around us crystallisation process of separating components of a mixture physical changes

A synthetic indicator phenolphthalein gives ________ colour in basic solution.

  1. red

  2. blue

  3. pink

  4. colourless
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Phenolphthalein [3,3-Bis (4- hydroxyphenyl) - 2 benzofuran- 1-one] is often used as an indicator in acid-base titrations. It turns colourless in acidic solutions and pink in basic solutions. Phenolphthalein is slightly soluble in water and usually dissolved in alcohols for use in experiments. It is a weak acid which can loose $H^{+}$ ions in solution. Phenolphthalein molecule is colourless and phenolphthalein ion is pink in colour. When a base is added to phenolphthalein, the molecule turns in to ions leading to more ionization as $ H^{+} $ ions are removed.