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2 years ago

A sample of helium gas has a volume of 2.75 L at STP. How many grams of He are present?

1 answer:

4 0

Molar mass He = 4.0 g/mol

1 mole --------- 22.4 L ( at STP )
? mole ---------- 2.75 L

2.75 x 1 / 22.4 => 0.1227 moles

1 mole He ------------ 4.0 g
0.1227 moles --------- ?

0.1227 x 4.0 / 1 => 0.4908 g of He

hope this helps!

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(I)how many atoms are present in 7g of lithium?

ICE Princess25 [194]

Answer :

(i) The number of atoms present in 7 g of lithium are, $6.07\times 10^{23}$

(ii) The number of atoms present in 7 g of lithium are, $1.204\times 10^{24}$

(iii) The number of moles of $F_2$ is, 1 mole

The number of moles of $CO_2$ is, 0.5 mole

The number of moles of $OH^-$ is, 1 mole

Explanation :

Part (i) :

First we have to calculate the moles of lithium.

$\text{Moles of }Li=\frac{\text{Mass of }Li}{\text{Molar mass of }Li}$

Molar mass of Li = 6.94 g/mole

$\text{Moles of }Li=\frac{7g}{6.94g/mol}=1.008mole$

Now we have to calculate the number of atoms present.

As, 1 mole of lithium contains $6.022\times 10^{23}$ number of atoms

So, 1.008 mole of lithium contains $1.008\times 6.022\times 10^{23}=6.07\times 10^{23}$ number of atoms

Thus, the number of atoms present in 7 g of lithium are, $6.07\times 10^{23}$

Part (ii) :

First we have to calculate the moles of carbon.

$\text{Moles of }C=\frac{\text{Mass of }C}{\text{Molar mass of }C}$

Molar mass of C = 12 g/mole

$\text{Moles of }C=\frac{24g}{12g/mol}=2mole$

Now we have to calculate the number of atoms present.

As, 1 mole of carbon contains $6.022\times 10^{23}$ number of atoms

So, 2 mole of carbon contains $2\times 6.022\times 10^{23}=1.204\times 10^{24}$ number of atoms

Thus, the number of atoms present in 7 g of lithium are, $1.204\times 10^{24}$

Part (iii) :

To calculate the moles of $F_2$ :

$\text{Moles of }F_2=\frac{\text{Mass of }F_2}{\text{Molar mass of }F_2}$

Molar mass of $F_2$ = 38 g/mole

$\text{Moles of }F_2=\frac{19g}{19g/mol}=1mole$

Thus, the number of moles of $F_2$ is, 1 mole

To calculate the moles of $CO_2$ :

$\text{Moles of }CO_2=\frac{\text{Mass of }CO_2}{\text{Molar mass of }CO_2}$

Molar mass of $CO_2$ = 44 g/mole

$\text{Moles of }CO_2=\frac{22g}{44g/mol}=0.5mole$

Thus, the number of moles of $CO_2$ is, 0.5 mole

To calculate the moles of $OH^-$ ions :

$\text{Moles of }OH^-=\frac{\text{Mass of }OH^-}{\text{Molar mass of }OH^-}$

Molar mass of $OH^-$ = 17 g/mole

$\text{Moles of }OH^-=\frac{17g}{17g/mol}=1mole$

Thus, the number of moles of $OH^-$ is, 1 mole

4 0

2 years ago

Pete drives 150 meters in 18 seconds what is his speed in meters per second

Vladimir [108]

Well, you would have to divide 150 metres by 18 seconds.

150/18 = 8 1/3 m/s OR 8.333 m/s

4 0

2 years ago

Calculate the volume that a 0.323-mol sample of a gas will occupy at 265 K and a pressure of 0.900 atm. 4.36 L 4.36 L 4.63 L 4.6

ikadub [295]

The volume that a 0.323-mol sample of a gas will occupy at 265 K and a pressure of 0.900 atm is 7.81L.

<h3>HOW TO CALCULATE VOLUME?</h3>

The volume of a gas can be calculated using the following formula:

PV = nRT

Where;

P = pressure (atm)
V = volume (L)
R = gas law constant (0.0821 Latm/molK)
n = number of moles
T = temperature (K)

V = 0.323 × 0.0821 × 265 ÷ 0.900

V = 7.027 ÷ 0.9

V = 7.81L

Therefore, the volume that a 0.323-mol sample of a gas will occupy at 265 K and a pressure of 0.900 atm is 7.81L.

Learn more about volume at: brainly.com/question/1578538

4 0

1 year ago

The carbon-14 radioisotope has proved most useful in:

valkas [14]

Measuring the amount of radiation in an area

8 0

2 years ago

Identify the chemical reaction Below: Ca(OH)2 + HCI CaCl2 + H20

belka [17]

Answer:

Neutralizaion reaction!

Explanation:

Calciumhydroxide under Hydrochloric acid gives Calciumchloride with the formation of water.

3 0

2 years ago