2NH 3 +H 2 SO 4 ="=" (NH 4 ) 2 SO 4?
34 98?
x? 50g×9.8%? 34/ x? = 98/50g×9.8%? ( 1)
X = 1.7g The mass of ammonia gas is 1.7g? ( 1)
(2)N % =( 1.7g× 14/ 17)/ 100g× 100%? = 1.4%? (2 points)
(3) 1.92% ~ 4% ( 1) ∵ 1.4% ∵ 1.92%? ∴ Milk powder is unqualified? ( 1)
(4) It is assumed that at least yg melamine needs to be added.
100g× 1.4% ﹢y×84/ 126? = (100g-y) ×1.92% (2 points)
y = 0.8g? Add at least 0.8g melamine (1 min).
Analysis: (1) According to the chemical equation of the reaction between ammonia and sulfuric acid, calculate the mass of ammonia from the mass of sulfuric acid consumed by absorbing ammonia;
(2) According to the method of detecting protein, the mass of N element in absorbed ammonia is 100g of milk powder sample, and the calculation can be completed by using the mass fraction of N element in milk powder = × 100%;
(3) According to the average mass fraction of nitrogen in protein is 65438 06%,
Using the mass fraction of nitrogen in milk powder = × 100%, the mass fraction range of nitrogen in milk powder containing protein 12g ~ 25g 100g was calculated. Comparing the mass fraction of N element in the milk powder sample with the national standard to judge whether the milk powder is qualified or not;
(4) After melamine is added to the milk powder, part of the N element comes from protein in the milk powder, and the other part comes from the added melamine. The addition amount is calculated when the mass fraction of N element in the added milk powder reaches the national minimum standard.
Solution: (1) Let the mass of ammonia produced be X.
Ammonium bicarbonate+sulfuric acid/(NH
34 98
x? 50g× 9.8%
x= 1.7g
(2) Nitrogen content in milk powder = × 100%= 1.4%.
(3) Every 100g of milk powder contains protein 12g, and the mass fraction of nitrogen in milk powder = × 100%= 1.92%.
Every 100g of milk powder contains 25g of protein, and the mass fraction of nitrogen in milk powder = × 100%=4%.
The mass fraction of nitrogen in qualified milk powder is 1.92% ~ 4%,
∵ 1.4%< 1.92%
Unqualified milk powder
(4) making the mass of melamine to be added at least Y.
100g× 1.4%﹢y×× 100%=( 100g﹢y)× 1.92%?
y=0.8g
Answer: (1) The mass of ammonia is1.7g; ;
(2) The content of nitrogen in milk powder is 65438 0.4%;
(3) the milk powder is unqualified;
(4) At least 0.8g melamine should be added.