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Put 20.8g mixture of zinc and zinc sulfate (without crystal water) into 179.6g dilute sulfuric acid, and then completely react to obtain 200g unsaturated zinc sulfate solution. Calculate the mass fraction of zinc sulfate in the solution 20% Find out the calculation process
According to the law of conservation of mass, the hydrogen generated is 20.8 + 179.6-200 = 0.4g
Zn+H2SO4=H2+ZnSO4
65 2 161
X 0.4g Y
X=13g Y=32.2g
ZnSO4:20.8-13+32.2=40g
w=40g/200g×100%=20%
In order to determine the content of sodium carbonate in edible flour soda, Li Tong designed and carried out the following experiments: 1. Weigh 3.4g flour soda sample in a beaker, add 20ml water and stir until the sample is completely dissolved; 2. Add enough CaCl2 solution to it until no precipitation is formed; 3. Filter and remove the precipitate After drying, the weight is 3.0g (regardless of the mass loss in operation). Please calculate: what is the mass fraction of Na2CO3 in edible flour alkali? (accurate to 0.1%)
Let the mass fraction of sodium carbonate in edible noodle soda be x.na2co3 + CaCl2 = CaCO3 ↓ + 2nacl106 & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; 1003.4g × X & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; 3.0g106100 = 3.4g × x3.0g, X ≈ 93.5%. A: the mass fraction of sodium carbonate in edible noodle soda is 93.5%
Uncle Zhang typed a manuscript. In the first two hours, he typed nine pages in total. In the second three hours, he typed four pages per hour. How many pages per hour does Uncle Zhang average?
The sum of 9 plus 3 times 4 divided by 5 equals 4.2 pages
A and B move in the same direction at the same point on a circle with a diameter of 100 meters. A walks 18.84 meters per minute, B walks 12.56 meters per minute. How many minutes can b catch up with a
Circumference = 3.14 × 100 = 314m
B can catch up with a in a few minutes
314 ÷ (18.84-12.56) = 50 minutes to catch up
If you understand and solve your problem,
It's better to calculate by recursion
（789325+5562122）÷78×456
=6351447÷78×456
=81428.807692307692307692307692308×456
=37131536.307692307692307692307692
Is that right
School is about to start, and there are only 14 practical problems left in Grade 5 of primary school! The prawn is willing to help, right! The most important thing is to have answers!
Teach you a move: change the data of the topic
Two students went to play and shared the car rental fee. When it was about to start, three students came to share the car rental fee with 15 people. As a result, the original 12 people were less than 1 yuan each. How much is the car rental fee?
1 × 12 = 12 yuan
12 △ 3 = 4 yuan / person
4 × 15 = 60 yuan
A: the rental fee is 60 yuan
Car a and car B leave each other from the two places. Car a travels 69 kilometers per hour, and car B 72 kilometers per hour. Car a leaves one hour later, and car B starts. What's the distance between the two places?
69 × (1 + 3) + 72 × 3 = 492km
One day after the heavy snow, Xiaoguang and his father measured the circumference of a circular flower garden. They walked the same starting point, route, direction, and the same size of shoes. Xiaoguang's step length was 54 cm, and his father's step length was 72 cm. Because their footprints overlapped, only 60 footprints were left on the snow. Find the perimeter of the flower garden
54 = 18 × 372 = 18 × 454 and the least common multiple of 72 = 18 × 3 × 4 = 216, so the footprints of 216 cm are overlapped once (excluding the footprints of the starting point), leaving 216 △ 54 + 216 △ 72-1 = 4 + 3-1 = 6 on the snow; 60 △ 6 = 10 (Times), and the perimeter of the flower bed is 216 × 10 = 2160 (CM); a: the perimeter of the flower bed is 2160 cm
If 13 is 30, then 16 is ()
A. 15B. 60C. 540
30 △ 13 × 16, = 90 × 16, = 15
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