Weigh 2g of crude salt (accurate to 0. 1 g) with a tray balance. Measure10ml of water with a measuring cylinder and pour it into a beaker. Add a spoonful of crude salt to the water with a medicine spoon and stir it with a glass rod to observe the phenomenon (what role does the stirring of the glass rod play in the dissolution of crude salt? Stir to accelerate dissolution). Then add the crude salt, stir with a glass rod while adding it until the crude salt no longer dissolves. Observe whether the solution becomes turbid. Weigh the remaining crude salt on the balance and calculate how many grams of crude salt are dissolved in 10 ml water.

Step 2 filter

After folding the filter paper, dip it in water with a glass rod to make it cling to the inner wall of the funnel, make the upper edge of the filter paper lower than the funnel mouth, make the liquid level of the solution lower than the upper edge of the filter paper, make the beaker mouth for pouring the liquid cling to the glass rod, make the end of the glass rod cling to one side with three layers of filter paper, and make the end of the funnel cling to the inner wall of the beaker for receiving filtrate. Pour the liquid slowly. When there is no water in the filter paper, carefully observe the residue on the filter paper and the color of the filtrate. When the filtrate is still turbid, it should be filtered again.

If the filtrate is still turbid after two times of filtration, check the device and analyze the reasons, for example, the filter paper is damaged, the liquid level in the funnel is higher than the edge of the filter paper during filtration, and the instrument is unclean. After finding out the reasons, operate again.

Step 3 evaporate

Pour the clarified filtrate into an evaporating dish. Place the evaporating dish on the iron ring of the iron frame and heat it with alcohol lamp.

At the same time, the filtrate is continuously stirred with a glass rod (evenly heated to prevent liquid splashing).

When a large amount of solids appear in the evaporating dish, stop heating. Use the waste heat of the evaporating dish to evaporate the filtrate.