Chemistry in the third year of junior high school, 3 and 4 questions will help to solve them.

3.Solution: 100g of national standard milk powder:

Contains protein of a mass of.

The mass of the nitrogenous element is *16% =

Suppose the protein content of 100g of milk powder is x

x :2x = The protein content of the milk powder is lower than the national standard due to <.

Solution: The distance traveled by the person in a year = 5 km days 365 days = l 825 km The energy consumed by the person in a year = 170 kJ km 1 825 km = 3l0 250 kj

The amount of fat consumed by this person in a year = 310 250 kj 32 200 kj kg = 9 635 1 kg = 9 64 kg

A: The mass of fat consumed by this person in 1 year (measured in 365 days) is approximately.

The protein content of the national standard milk powder = , the nitrogen content is.

The milk powder has a nitrogen content of 2% and a protein content of 2% 16% =, which does not meet.

A CA should be m>n>p

The discoloration range of phenolphthalein is as follows, and only the m spot is red.

This generally available chemical equation is mainly that proteins will denature and precipitate when they encounter heavy metals, preventing heavy metals from being absorbed by the human body.

sodium hydroxide excess); NaOH+SO2==NaHSO3 (a small amount of sodium hydroxide);

2naoh+co2==na2co3+h2o;(Actually, the same as SO2) 3(1) Graduated cylinder, rubber tip dropper; (2) Add 1-2 drops of phenolphthalein as an indicator.

3) Match: first calculate the mass of NaOH as; According to the chemical equation, it can be calculated: 60 m=40 m=; And the quality of the acetic acid solution is; So the mass fraction of acetic acid is.

1) The correct is a reason that heavy metals will complex with proteins to denature proteins, so egg whites are taken to prevent protein denaturation in the body, and there is no specific chemical equation;

2）2naoh+co2=na2co3+h2o;2naoh+so2=na2so3+h2o;2naoh+sio2=na2sio3+h2o

3) (1) NaOH + CH3COOH = CH3COONA + H2O Experimental procedure (1) Rubber tip dropper and graduated cylinder.

2) Add 1-2 drops of phenolphthalein indicator Data processing Consumption of sodium hydroxide 40ml*1g ml*1%= The amount of the converted substance is, so the total amount of acetic acid reacted with it is converted to mass, so the mass fraction of the acetic acid solution is, which is consistent with the label labeling.

The oxidation of glucose in the body is not burning, the combustion is only vigorous oxidation.

Magnesium reacts with oxygen, nitrogen, and carbon dioxide in the air, but not with hydrogen and rare gases.

3.No carbon dioxide dissolves in water to form carbonic acid.

d. The intensity of the combustion of substances is related to the concentration of oxygen.

b. Larger than the mass of the magnesium belt c, equal to the quality of the magnesium belt participating in the reflection plus the quality of oxygen participating in the reflection cannot.

1. The mass of the remaining substance after the evaporation of water: 84g-25g=59g, the mass of the precipitated crystal:

Solubility = 2Because water in the original solution is superfluous and can dissolve 5g of the substance, s=5g with one decimal place).

3.The first evaporation is an unsaturated solution, and the second is a saturated solution, so s=3g 5g*100g=60g

Analysis: (1) The solution gradually fades from yellow to colorless, and there is a reddish-brown precipitate.

2）fecl3 + 3naoh → fe（oh）3↓ +3nacl（3）nacl、naoh

4) Let the consumed HCl mass be X G, then there is:

hcl + naoh → nacl + h2ox g 16 g × 10%

Solution: x = g

Therefore, the HCl mass fraction in industrial hydrochloric acid = g 20 g) 100 %.

The answer should be this