(2) solution: let the mass of CaCO in the scale be x.

CaCO 3 +2HCl==CaCl 2 +H 2 O+CO 2

100 ? Forty-four

x？ 3.3g

x=7.5g

The mass fraction of CaCO in scale is:

A: The mass fraction of CaCO 3 in this scale is 75%.

Analysis: (1) Calculate the mass of hydrochloric acid according to the constant amount of solute during dilution, find out the volume, and select the required measuring cylinder;

(2) According to the existing knowledge, calcium carbonate can react with hydrochloric acid to generate carbon dioxide, while magnesium hydroxide reacts with hydrochloric acid to generate magnesium chloride and water, and no gas is generated. According to the data provided in the table, the quality of calcium carbonate can be obtained, so that the content of calcium carbonate can be obtained.

(1) According to the mass of concentrated solution × mass fraction of concentrated solution = mass of dilute solution × mass fraction of dilute solution,

The required hydrochloric acid mass = =27.0g, the volume is 27.0g÷1.18g/cm3 = 23cm3 = 23ml, and a 50mL measuring cylinder is selected;

(2) No matter whether the sample of 10g is pure calcium carbonate or magnesium hydroxide, the hydrochloric acid required for complete reaction does not exceed 10g, so the hydrochloric acid is excessive. Calcium carbonate can react with hydrochloric acid to produce carbon dioxide, but magnesium hydroxide can't. When the gas mass does not change, it means that calcium carbonate has completely reacted, so the reaction is completed after 4 minutes.

Let the mass of calcium carbonate required to produce 3.3g carbon dioxide be x.

Calcium carbonate+2 HCl/CaCl2+carbon dioxide =+water

100 44

x 3.3g

x=7.5g

The mass fraction of CaCO in scale is:

7.5g

10.0g

× 100%=75%

Answer: (1)27.0, 50mL；;

(2) Answer: The mass fraction of CaCO 3 in this scale is 75%.