All the reagents are in excess except the final hydrochloric acid which is in the right amount.

Related equations

②?BaCl2?+?Na2SO4?=?BaSO4↓ + 2 NaCl

③?MgCl2?+ 2 NaOH =?Mg(OH)2↓ + 2 NaCl

④?CaCl2?+?Na2CO3?=?CaCO3↓ + 2 NaCl; BaCl2?+?Na2CO3?=?BaCO3↓ + 2 NaCl

⑤ NaOH + HCl = NaCl + H2O; Na2CO3?+ 2 HCl = 2 NaCl + CO2↑ + H2O

. Extended information:

Crude salt contains insoluble impurities such as silt and sand, and soluble impurities such as Ca2+, Mg2+, SO42-? etc. Insoluble impurities can be removed by filtration, while soluble impurities such as Ca2+, Mg2+, SO42- can be removed by adding BaCl2, NaOH and Na2CO3 solution to produce precipitation, or by adding BaCO3 solid and NaOH solution. The water is then evaporated to obtain a purer refined salt.

Procedure

Weigh 2 grams of crude salt (to the nearest 0.1 gram) on a pallet balance. Measure 10 ml of water with a measuring cylinder and pour it into a beaker. Take a spoonful of coarse salt with a medicine spoon and add it to the water and stir it with a glass rod and observe the phenomenon (What role does the stirring of the glass rod play in dissolving the coarse salt? (Stirring speeds up the rate of dissolution). Next, add more coarse salt, stirring with the glass rod as you go, until the coarse salt no longer dissolves. Observe whether the solution becomes cloudy.

1. Weigh the remaining coarse salt on a balance and calculate the approximate number of grams of coarse salt dissolved in 10 milliliters of water.

2. Add excess BaCl2 (to remove sulfate ions) BaCl2+Na2SO4==BaSO4↓+2NaCl

3. Add excess NaOH (to remove magnesium ions) MgCl2+2NaOH==Mg(OH)2↓+2NaCl

4. Add excess Na2CO3 (to remove calcium and Barium ions in BaCl2) Na2CO3+CaCl2==CaCO3↓+2NaCl

5. Na2CO3+BaCl2==BaCO3↓+2NaCl

(Note: Interchangeable 2, 3 two steps or 3, 4 two steps. the amount of Na2CO3 must remove all the BaCl2, you can use the pH test paper to control the (Add the amount.)

6 filtration

To the filtrate add appropriate amount of HCl (to remove excess NaOH, Na2CO3, you can choose to use pH test paper to control the amount added, or direct evaporation)

7. evaporation of crystals

filtration to pay attention to a post, two low, three leaning.

①"A stick" means that the angle of folding the filter paper to match the caliber of the inner wall of the funnel, so that the wet filter paper close to the inner wall of the funnel without bubbles, because if there are bubbles will affect the filtration speed.

② "two low" refers to the edge of the filter paper to be slightly lower than the edge of the funnel, the second is the entire filtration process, but also always note that the liquid surface of the filtrate is lower than the edge of the filter paper. This can prevent impurities unfiltered and flow directly into the beaker, so that the unfiltered liquid and filtrate mixed together, and make the filtrate turbid, did not achieve the purpose of filtration.

③ "three against" one means that the liquid to be filtered when poured into the funnel, beaker beakers of liquid to be filtered beaker mouth to lean on the tilt of the glass rod (glass rod diversion), to prevent splashing and liquid to be filtered to break through the filter paper; the second refers to the lower end of the glass rod should be gently leaning against the three layers of filter paper in order to prevent breaking the filter paper (three layers of filter paper). One side is thicker than the other side of a layer of filter paper, three layers of filter paper side is not easy to be broken); Third, the neck of the funnel should be close to the receiver of the filtrate receiver wall, in order to prevent the liquid from splashing out.

Calculation of yield

Calculate the yield of refined salt by comparing purified sodium chloride with crude salt.

(Error analysis: Significantly low: A. The crude salt was poured into the water all at once during dissolution and filtered immediately B. Some liquid and solids were spilled during evaporation.C. The solids were not completely transferred to the paper.

High: The purified salt is weighed before it is completely dry. The crude salt contains other soluble solids.)

The role of glass rods

Glass rods were used 5 times in this experiment.

1. When dissolving: stirring to accelerate dissolution.

2. Before filtering: moisten the filter paper by dipping it in water.

3. When filtering: drain.

4. When evaporating: stirring, so that the liquid is evenly heated, to prevent the liquid from splashing.

5. in calculating yield: transferring the solid to paper with a glass rod.

(Be careful not to touch the wall of the glass when stirring the glass rod)

Reference: