Tag: basic analytical techniques

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Questions Related to basic analytical techniques

Multiple choice chemistry basic analytical techniques filtration and crystallisation other methods of separation separation techniques

Which of the following can undergo sublimation?

  1. Iodine crystals

  2. Camphor

  3. Naphthalene balls

  4. All of above
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

There are many substances which are converted into gas from solid when heated, and converted from gas to solid when cooled without converting into liquid. Such substances are known as sublime. For example, ammonium chloride, naphthalene balls, camphor, etc.

Multiple choice chemistry basic analytical techniques filtration and crystallisation other methods of separation separation techniques

What is observed when a mixture of common salt and ammonium chloride is heated?

  1. Solid common salt gets deposited on the cooler parts of the funnel, while solid ammonium chloride remains in the china dish

  2. Mixture of common salt and ammonium chloride turns into greenish crystals when allowed to cool

  3. Ammonium chloride is deposited on the cooler parts of the funnel and solid common salt remains in the china dish

  4. Droplets containing both common salt and ammonium chloride appear on the upper part of the funnel, while some molten mixture of common salt and ammonium chloride remains in the china dish
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Sublimation is the transition of a substance directly from the solid to the gas phase without passing through the intermediate liquid phase. Ammonium chloride, camphor, anthracene, napthalene can sublime but common salt cannot sublime. Ammonium chloride evaportaes and forms vapours which rise up the funnel and get deposited in the cooler parts of the funnel. Sodium chloride remains in the china dish as no reaction takes place.

Multiple choice chemistry basic analytical techniques filtration and crystallisation other methods of separation separation techniques

Why does the dish should be properly plugged during sublimation?

  1. To let the vapors escape

  2. To prevent escaping of vapors

  3. To restrict sublimation

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

If the dish in not plugged properly during sublimation, the vapors will escape and cannot be converted into solid on cooling. Thus, separation becomes difficult.

Multiple choice chemistry basic analytical techniques filtration and crystallisation other methods of separation separation techniques

After sublimation of ammonium chloride, how can salt be separated from the filtrate?

  1. Condensation

  2. Chromtography

  3. Evaporation

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

Evaporation technique is used to separate salt from the filtrate. Common salt does not decompose during evaporation. As the water evaporates, fewer and fewer water molecules are present to keep the salt particles apart. The salt, therefore, recrystallizes and can be collected. 

Multiple choice chemistry basic analytical techniques filtration and crystallisation other methods of separation separation techniques

All the impurities after crystallization are left behind in:

  1. mother liquor

  2. impurity solution

  3. dirt liqour
  4. both $B$ and $C$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In crystallisation, the impure substance is dissolved in a suitable solvent to reach its nearly saturated solution at a temperature higher than the room temperature. At this high temperature, the solute has very high solubility in that solvent, so a much smaller quantity of hot solvent is needed for dissolving the solute than the solvent at room temperature.  When the solution is cooled, the pure substance is crystallised. The solution left behind is called mother liquor. All the impurities are left behind in the mother liquor. The purification method depends on the differences in solubility between the compound and the impurity.     

Multiple choice chemistry basic analytical techniques filtration and crystallisation other methods of separation separation techniques

In fractional crystallization the proportion of components in the precipitate will depend on their solubility product.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Fractional crystallization is the method of refining substances based on the differences in their solubility. If a mixture of two or more substances in a solution is allowed to crystallise, the least soluble substance will crystallise first. The proportion of the components in the precipitate will depend on their solubility product.

Multiple choice chemistry basic analytical techniques filtration and crystallisation other methods of separation separation techniques

A separating funnel is used to separate the components of a mixture of:

  1. iodine and sugar

  2. ethanol and water

  3. cooking oil and water

  4. ammonium chloride and iron filings
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

A separating funnel is used to separate the components of a mixture of cooking oil and water. A separating funnel is used to separate the components of a mixture of two immiscible liquids. Cooking oil and water are two immiscible liquids.

Multiple choice chemistry basic analytical techniques filtration and crystallisation other methods of separation separation techniques

A public health inspector suspects that in addition to two harmless dyes (boiling points $69\ ^oC$ and $71\ ^oC$), a lollipop also contains a poisonous green dye (boiling point $73\ ^oC$). Which of the following can be used to confirm his suspicion?

  1. Fractional distillation

  2. Paper chromatography

  3. Filtration

  4. Crystallization
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A public health inspector suspects that in addition to two harmless dyes(boiling points 69 C and 71 C), a lollipop also contains a poisonous green dye (boiling point 73 C). Paper chromatography can be used to confirm his suspicion. Here, different dyes will have different affinity for paper (stationary phase) and solvent (mobile phase). Fractional distillation is used when individual components of mixtures have boiling points more than 30 C. Filtration and crystallisation are used in separation / purification of solid from liquid.