(12) (20 12? In order to determine the CuO content in the copper oxide sample used in the "carbon reduction of copper oxide" experiment, Maoming's interest group conducted the following experiment.

(1) hydrochloric acid; CuCl 2； (2)4.8g； (3) Answer: The mass fraction of solute in sodium hydroxide solution is 8%.

(1) After sodium hydroxide was put in, there was no precipitation at first, so the added NaOH first reacted with hydrochloric acid in the filtrate and then with copper chloride in the solution to generate copper hydroxide precipitation.

(2) According to the equations CuO+2HCl═CuCl 2 +H 2 O and CuCl 2 +2NaOH═Cu(OH) 2 ↓+2NaCl, each molecule of copper oxide can eventually generate 1 molecule of copper hydroxide, so the relation of CuO ~ Cu (OH) 2 can be established;

Let the mass of copper oxide in the sample be x.

CuO~Cu(OH) 2 80？ 98

x？ 5.88 grams

X = 4.8g

(3) Let the mass of sodium hydroxide reacting with copper chloride be y..

Cuprous chloride 2+2 NaOH Cu (OH) 2 ↓+2 sodium chloride

80? 98

Y5.88g.

y=4.8g

Therefore, the mass fraction of solute in sodium hydroxide solution = × 100%=8%.