1 points sorted
Crude salt contains insoluble impurities (such as sediment) and soluble impurities (such as MgCl2, CaCl2, etc.), the purification of crude salt includes crude extraction and fine extraction. Crude extraction through filtration to remove sand and other insoluble impurities, and then evaporate the water, that is, to obtain the "refined salt". In fine extraction, the soluble impurities in the solution of "fine salt" can be removed gradually by choosing suitable impurity removal reagents (excess). At the same time, in the subsequent operation of the excess of the removal reagent should also be completely removed.
1.1 The removal of insoluble impurities in the crude salt - crude extraction
(1) Instruments: medicine spoon, tray balance, beaker, glass rod, funnel, iron stand (including iron ring), evaporation dish, alcohol lamp, crucible clamp.
(2) Steps: dissolution, filtration, evaporation and crystallization yield calculation.
(3) 4 roles of glass rod.
(1) Dissolving: stirring, accelerate the dissolution of crude salt; (2) filtration: drainage, to prevent the liquid from splashing; (3) evaporation: to prevent heating due to local overheating, resulting in droplet splashing; (4) after evaporation: transfer of solids. to Mg (OH) 2, CaCO3 precipitate.
(2) Filter to remove Mg (OH) 2, CaCO3 precipitate.
(3) Add appropriate amount of dilute hydrochloric acid to the filtrate to remove excess NaOH, Na2CO3, and convert them to NaCl.
(4) Heat and evaporate, remove excess HCl and solvent water, and get NaCl crystals.
2 Examination forms
2.1 Examination of the removal of insoluble impurities in crude salt
Example 1 The ocean is a huge treasure trove of resources, from which many substances can be obtained, Lianyungang is rich in seawater resources.
Crude salt obtained by drying seawater contains a variety of soluble impurities and insoluble impurities (sediment, etc.). In the laboratory to remove the insoluble impurities in the crude salt to obtain refined salt steps are: dissolution, filtration, evaporation and calculate the yield.
(1) In the filtration operation, the end of the glass rod should be gently angled to the _______ side. To prevent droplets from splashing during evaporation, in addition to stirring with a glass rod, the operation can be taken _______.
(2) The following operation may lead to high yield of refined salt is _____ (fill in the letter).
a. The salt is not completely dissolved that is filtered
b. The liquid level is higher than the edge of the filter paper during filtration
c. Not all of the refined salt adhering to the vessel is transferred to the weighing paper
Analysis:This question examines the steps in the purification of crude salt. Involving the following points: the purification of crude salt filtration and evaporation precautions; experimental error analysis and other knowledge. Specific analysis is as follows: (1) filtration operation, in order to prevent the breakage of the filter paper, the end of the glass rod should be gently leaning against the side of the three layers of filter paper. In order to prevent droplets from splashing when evaporating, in addition to stirring with a glass rod, you can also take the operation is to remove the alcohol lamp. Salt is not completely dissolved that filtration, will lead to part of the loss of salt, resulting in the production of refined salt yield is low; filtration of the liquid surface above the edge of the filter paper, will lead to part of the insoluble substances remain in the salt, resulting in the production of refined salt yield is high; the vessel is not all the sticking of the refined salt to the weighing paper, will lead to the quality of the refined salt is small, resulting in the production of refined salt yield is low.
Answer: (1) three layers of filter paper, remove the alcohol lamp; (2) b.
2.2 Removal of soluble impurities from a solution of refined salt
Example 2: Preparation of refined salt from crude salt (containing the impurities Na2SO4, MgCl2, CaCl2 and silt).
(1) Add water to dissolve, with the device shown in Figure 2 to remove the sediment in the crude salt, the role of the glass rod is _______.