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4 years ago

Why is it that the north star is the only star in the night sky that seems to stay still

1 answer:

8 0

I think it is because it is directly about the north or south pole (I forget) so while all the other stars seem to rotate around because the Earth is rotating but the North Star is directly in the center. Don't take my word though.

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Ammonia is formed according to the reaction below. A chemist mixes 21 grams of nitrogen gas and 18 grams of hydrogen gas in a 2.

Rama09 [41]

Answer : The mass of hydrogen gas consumed will be, 4.5 grams

Explanation : Given,

Mass of $N_2$ = 21 g

Mass of $H_2$ = 18 g

Molar mass of $N_2$ = 28 g/mole

Molar mass of $H_2$ = 2 g/mole

First we have to calculate the moles of $N_2$ and $H_2$ .

$\text{Moles of }N_2=\frac{\text{Mass of }N_2}{\text{Molar mass of }N_2}=\frac{21g}{28g/mole}=0.75moles$

$\text{Moles of }H_2=\frac{\text{Mass of }H_2}{\text{Molar mass of }H_2}=\frac{18g}{2g/mole}=9moles$

Now we have to calculate the limiting and excess reagent.

The balanced chemical reaction is,

$N_2(g)+3H_2(g)\rightarrow 2NH_3(g)$

From the given balanced reaction, we conclude that

As, 1 mole of $N_2$ react with 3 moles of $H_2$

So, 0.75 moles of $N_2$ react with $3\times 0.75=2.25$ moles of $H_2$

From this we conclude that, $H_2$ is an excess reagent because the given moles are greater than the required moles and $N_2$ is a limiting reagent because it limits the formation of product.

The moles of hydrogen gas consumed = 2.25 mole

Now we have to calculate the mass of hydrogen gas consumed.

$\text{Mass of }H_2=\text{Moles of }H_2\times \text{Molar mass of }H_2$

$\text{Mass of }H_2=(2.25mole)\times (2g/mole)=4.5g$

Therefore, the mass of hydrogen gas consumed will be, 4.5 grams

5 0

3 years ago

A prairie dog runs into its burrow as a coyote approaches.This behavior helps the prairie dog

Nookie1986 [14]

This behavior helps the prairie dog from being prey upon by coyote.
Prairie dogs live in burrow and they normally do not move much away from their burrows. When they sense danger they will dash quickly back into their burrows. This behavioral adaptation protect them from predators.

4 0

4 years ago

Explain the trend in boling point of alcohols in their homologous series

faltersainse [42]

Explanation:

The boiling point of alcohols also increase as the length of hydrocarbon chain increases

4 0

3 years ago

If a candy bar contains 345 Calories, how many calories is this?

Arisa [49]

Answer: 345,000 calories

Explanation:

Calories in food such as candy bars refer to the amount of energy that the food has. Calories are also called Kilocalories because they are the equivalent of 1,000 calories.

If the candy bar contained 345 calories therefore, and 1 Calorie is 1,000 calories, the calories in the candy bar are:

= 345 * 1,000

= 345,000 calories

4 0

3 years ago

27.8 mL solution of 0.797 M HCHO2 with 0.928 M NaOH. What is the pH for the solution at the equivalence point in the titration?

kati45 [8]

Answer:

8.69 is the pH at the equivalence point

Explanation:

Formic acid, HCHO₂, reacts with NaOH as follows:

HCHO₂ + NaOH → NaCHO₂ + H₂O.

At the equivalence point you will have in the reaction just NaCHO₂ and H₂O. The concentration of NaCHO₂ will be:

<em />

<em>Moles: </em>0.0278L * 0.797mol/L = 0.02216moles

To reach the equivalence point it is necessary to add:

0.02216mol * (1L / 0.928mol) = 0.0239L

Total volume in the equivalence point:

0.0278L + 0.0239L = 0.0517L

Concentration: 0.02216moles / 0.0517L = 0.429M

The equilibrium of NaCHO₂, CHO₂⁻, in water is:

CHO₂⁻(aq) + H₂O(l) ⇄ OH⁻(aq) + HCHO₂(aq)

Where Kb, 5.56x10⁻¹¹ is defined as:

5.56x10⁻¹¹ = [OH⁻] [HCHO₂] / [CHO₂⁻]

In the equilibrium, it is produced X OH⁻ and HCHO₂, and as concentration of NaCHO₂ is 0.429M:

5.56x10⁻¹¹ = [X] [X] / [0.429M]

2.383x10⁻¹¹ = X²

4.88x10⁻⁶ = X = [OH⁻]

As pOH = -log [OH⁻]

pOH = 5.31

And pH = 14 - pH

pH = 8.69 is the pH at the equivalence point

3 0

3 years ago