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Natali [406]
3 years ago
7

Why was helium absent from mendeleev's original periodic table of 1871?

Chemistry
1 answer:
34kurt3 years ago
6 0
<span>This is because it was not yet discovered during that time. Helium (noble gases) was extremely difficult to discover that time because it does not react with other elements. And now since Mendeleev had based his table on the similar properties of known elements he could not have included Helium in his table.</span>
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What is the mass in grams of 5.2 moles of NaCl?<br> 303.89 g<br> 0.09 g<br> 119.6 g<br> 1828
Vitek1552 [10]

Explanation:

mole=mass/molar mass

mass= mole×molar mass

m= 5.2×( 23+35.5)

m= 5.2×58.5

m= 304.2g

6 0
3 years ago
The solubility of a certain compound in ice-cold water is 0.16 g in 100 mL. Its solubility in hot water is 4.35 g in 100 mL. Wha
jonny [76]

Answer:

96.32 %

Explanation:

Given that:

The solubility of compound in hot water = 4.35 g / 100 mL

The solubility of compound in cold water = 0.16 g / 100 mL

Which means that in 100 mL of hot water, the dissolved compound is 4.35 g and in cold water, the dissolved compound is 0.16 g

Hence, on transition, compound that will catalyze is 4.35 - 0.16 g = 4.19 g

So,

\%=\frac {4.19}{4.35}\times 100

Percent recovery for re-crystallization of this compound from water= 96.32 %

3 0
3 years ago
Which statements describe the death of stars? Check all that apply.
Sveta_85 [38]

Answer:A and B

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5 0
3 years ago
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A 2-kg box is pushed from rest to a speed of 29.7 m/s in 21 seconds. What is the power require to accelerate the box.
Alona [7]

Answer:

P = 83.16 Watt

Explanation:

Given data:

Mass of box = 2 Kg

velocity of box = 29.7 m/s

Time = 21 sec

Power = ?

Solution:

Formula:

Power = work done/time

Now we will calculate the work done.

W = force × distance ...... (1)

d = speed /time

d = 29.7 m/s× 21 s

d = 623.7 m

Force:

acceleration = 29.7 m/s / 21 s

a = 1.4 m/s²

Force = m×a

Force = 2 kg×1.4 m/s²

Force = 2.8 N

Now we will put the values in equation 1.

W = F × d

W = 2.8 N ×623.7 m

W = 1746.36 Nm

Now for power:

P = W / time

P = 1746 Nm / 21 s

P = 83.16 Watt

5 0
3 years ago
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How many nickels are in 3 rolls of nickels
oee [108]

1 roll of nickels has 40 nickles.

40 * 3 = 120

120 nickels in 3 rolls of nickels.

3 0
3 years ago
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