Tag: basic analytical techniques

Questions Related to basic analytical techniques

Which of the following can undergo sublimation?

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

  1. Iodine crystals

  2. Camphor

  3. Naphthalene balls

  4. All of above

Show answer
Correct Option: D
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.

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

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

  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

Show answer
Correct Option: C
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.

Why does the dish should be properly plugged during sublimation?

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

  1. To let the vapors escape

  2. To prevent escaping of vapors

  3. To restrict sublimation

  4. None of above

Show answer
Correct Option: B
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.

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

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

  1. Condensation

  2. Chromtography

  3. Evaporation

  4. Sublimation

Show answer
Correct Option: C
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. 

Ammonium chloride doesnt actually undergo sublimation upon heating. 

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

  1. True

  2. False

Show answer
Correct Option: A
Explanation:

Ammonium chloride doesn't actually undergo sublimation upon heating. It decomposes and forms ammonia gas and hydrogen chloride gas.Thus the given statement is true.

Non volatile substances can undergo sublimation. 

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

  1. True

  2. False

Show answer
Correct Option: B
Explanation:

Sublimation is the process of transition of a substance from the solid to the gaseous state without passing through the liquid state. Non-volatile compounds cannot vaporise and hence, cannot undergo sublimation.

All the impurities after crystallization are left behind in:

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

  1. mother liquor 

  2. impurity solution

  3. dirt liqour

  4. both $B$ and $C$

Show answer
Correct Option: A
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.     

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

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

  1. True

  2. False

Show answer
Correct Option: A
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.

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

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

  1. iodine and sugar

  2. ethanol and water

  3. cooking oil and water

  4. ammonium chloride and iron filings

Show answer
Correct Option: C
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.

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?

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

  1. Fractional distillation

  2. Paper chromatography

  3. Filtration

  4. Crystallization

Show answer
Correct Option: B
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.