Henry's Law

According to Henry's Law, at a constant temperature the amount of a gas dissolved in a solvent is directly proportional to its partial pressure when it is in equilibrium with its liquid phase. 

Solutions & Solubility 

When an ionic solid dissolves, ions leave the solid and become dispersed in the solvent. This solution can be classified as saturatedunsaturated or supersaturated

Concept: Saturated, Unsaturated and Supersaturated Solutions. 

5m
Video Transcript

Welcome back, guys! In this new video, we're going to take a closer look at solubility. What we should realize is that solubility can have two other names associated with it. Solubility is also called concentration. If they say concentration, it's the same thing as solubility. Another name for concentration or solubility would be molarity. Molarity is moles of solute per liter of solution. Solubility is how much solute can we dissolve in our solvent. They're both basically saying the same exact thing.
When we dissolve a solid, what's going to happen is ions are going to leave that solid and basically dissolve within the solvent. What we should realize is that there’s basically a threshold, a limit to how much solute we can dissolve into something. After a certain point, we can try and try and try and add more and more solid but none of it is going to dissolve because the water, the liquid, has reached its maximum amount of dissolving.
We should realize that when it comes to this, there are different terms we need to be familiar with. We're going to say in a blank solution, the maximum amount of dissolved solute is present in the solvent. What I mean by this is let's say we have a bucket of water. Let’s say that this bucket of water can only dissolve up to 100 grams of solute. Let's say I take 102 grams of solute and I dump it into that bucket. The bucket will dissolve the hundred grams, no problem. But those extra two grams I have are not going to dissolve. They're going to remain as solids clumped up at the bottom of the bucket of water. We're going to say this solution has reached its maximum amount of solute. We're going to say that this solution is saturated. Remember, saturated means that the solution, the solvent, has reached its maximum amount in grams, in moles, whatever of the amount of solute it can dissolve successfully.
In a blank solution, additional amounts of solute can be further dissolved in the solvent. We have our same bucket of water. We say that it can dissolve 100 grams. But let's say I take 90 grams of solute and I dump it in there. All 90 grams will completely dissolve and we still have room to dissolve 10 more grams. We're going to say that this solution is unsaturated. It still has room for it to dissolve more solvent. It will successfully dissolve the 90 but we still have room for 10 more.
Finally, our last type we're going to say in this, in a blank solution more than the equilibrium concentration of solute has been dissolved. What this means is again I have my bucket of water and somehow I get this bucket even though it's supposed to only dissolve 100, I get it to dissolve those extra 2 grams I talked about earlier. We're going to say that this solution is supersaturated. It's gone beyond its limit. You might ask, how do we accomplish this? What you’re going to say here is to do this, you’d have to apply heat. Heat is needed to do this. If you supply heat to it, you'll be able to dissolve beyond your maximum.
But here's the thing. Supersaturated solutions are very unstable. The moment that I take away the heat from the solution, the extra 2 that I dissolved is going to re-solidify and form a precipitate or what we call a solid on the bottom. Remember, heat causes us to create a supersaturated solution. I can dissolve 102 grams, all 102 of it dissolves completely. Once I take away my heat, the extra 2 grams that I have here are going to form a precipitate. They're going to what we say recrystallize. They’re going to recrystallize at the bottom of my bucket of water.
Saturated, unsaturated, supersaturated – all of them deal with solubility, how much solute can I dissolve. All of them deal with molarity. Remember, solubility, concentration, molarity – all the same thing.

In a hypothetical solution 100 mL of water can dissolve up to 100 g of solute. In a SATURATED solution the water has reached its maximum amount of dissolve solute. 

In an UNSATURATED solution additional amounts of solute can be further dissolved in the solvent. 

In a SUPERSATURATED solution the solvent has dissolved beyond its maximum solubility. 

Example: Caffeine is about 10 times as soluble in warm water as in cold water. A student puts a hot-water extract caffeine into an ice bath, and some caffeine crystallizes. What is the identity of the solution before it’s been placed in an ice bath?

a) Saturated

b) Supersaturated

c) Unsaturated

d) Not enough information to answer the question. 

2m

Concept: Understanding Henry's Law

3m
Video Transcript

Connected to this is what we call Henry's law. Basically, Henry's law talks about how much gas can we get to dissolve in a solvent. Henry’s law explains the relationship between gas, pressure, and solubility. The solubility of a gas, and remember solubility just means molarity, is directly proportional to the partial pressure of the gas above the solution. All this means is if I increase my pressure, then I increase the solubility of my gas. Because you have to think about in this way. We have a couple of water or something, a bucket of water and we have gas particles above it, floating on top of it.
Here, this represents my pressure. If I push down on this piston, it’s going to push down against the gas. The gases have only one place to go. The gases will go into the liquid. The gas is dissolved in the liquid. That's what we mean by Henry's law. Basically if I increase my pressure, I increase how much gas I have in my solvent because they have no other place to go from pushing down on them.
We're going to say again, solubility of the gas means molarity of the gas. P here, P of the gas means the partial pressure of that gas. Partial pressure of that gas just means that’s the pressure of only that gas. In a container, we usually don't have one type of gas. We usually have a mixture of gases. Collectively, that is the total pressure. But each type with gas has its own individual pressure. That individual pressure is called partial pressure.
Then we're going to say kH here is known as Henry's constant. Together, all three of these give us Henry's law. Remember what solubility is and remember, increasing the pressure will increase the solubility of a gas. 

Henry's Law relates the solubility of a gas over a solution based on the factors of temperature, volume and pressure. 

Example: Henry’s Law Constant for nitrogen in water is 1.67 x 10-4 M•atm-1. If a closed canister contains 113 ppb nitrogen, what would be its pressure in atm? 

6m

As the temperature of the solution increases more and more gas molecules will exit the solvent. 

Problem: In general, as the temperature increases, the solubility of gas in a given liquid ________________, and the solubility of most solids in a given liquid ________________. 

a. Increases, increases

b. increases, decreases

c. decreases, increases

d. decreases, decreases

3m

Problem: At a partial pressure of acetylene 1.35 atm, 1.21 moles of it dissolves in 1.05 L of acetonitrile. If the partial pressure of acetylene in acetone is increased to 12.0 atm, then what is its solubility?

4m

Henry's Law Additional Practice Problems

What is the quantitative relationship between gas solubility and pressure?

a. Avogadro's Law

b. Entropy

c. Enthalpy

d. Boyle's law

e. Henry's law 

Watch Solution

At 25°C and 765 Torr, carbon dioxide has a solubility of 0.0342 M in water. What is its solubility at 25°C and 1210 Torr?

Watch Solution
Calculate the solubility of nitrogen in water at an atmospheric pressure of 0.41 atm (a typical value at high altitude). 


Watch Solution

Calculate the solubility (in M units) of ammonia gas in water at 298 K and a partial pressure of 3.50 bar. The Henry's law constant for ammonia gas at 298 K is 58.0 M/atm and 1 bar = 0.9869 atm. Express your answer in molarity to three significant figures.

Watch Solution

At 20° C and a partial pressure of 760 mmHg the solubility of CO2 in water is 0.169 g/100 mL. What is the solubility of CO2 at 2.7 x 104 mmHg?


Watch Solution

Suppose that you have made a saturated solution of this solute using 53.0 g of water at 20.0 °C. How much more solute can you add if the temperature is increased to 30.0 C?



Watch Solution

Why does the solubility of any gas in water decrease with rising temperature?

Watch Solution

At 298 K, the Henry's law constant for oxygen is 0.00130 M/atm. Air is 21.0% oxygen.

a) At 298 K, what is the solubility of oxygen in water exposed to air at 1.00 atm?
 

 

b) At 298 K, what is the solubility of oxygen in water exposed to air at 0.900 atm?
 

 

c) If atmospheric pressure suddenly changes from 1.00 atm to 0.900 atm at 298 K, how much oxygen will be released from 4.10 L of water in an unsealed container?

Watch Solution

A) What is the Henry's law constant for CO 2 at 20°C?

B) What pressure is required to achieve a CO 2 concentration of 9.60 x 10 -2?

C) At 1 atm, how many moles of CO2 are released by raising the temperature of 1 liter of water from 20∘C to 25∘C?

Watch Solution

Identify the TRUE statement describing trends in solubility.

a. Increasing the temperature of a solution increases the solubility of gases in solution.

b. Increasing the partial pressure of a gas above solution decreases the solubility of the gas in solution.

c. The solubility of a gas in a solution increases as its molar mass increases.

d. The solubility of most solids in solution increases as the pressure increases.

Watch Solution

The solubility of nitrogen gas at 25 °C and 1 atm is 6.8 × 10  -4 mol/L. If the partial pressure of nitrogen gas in air is 0.76 atm, what is the concentration (molarity) of dissolved nitrogen?

A. 6.8 × 10 -4 M

B. 5.2 × 10 -4 M

C. 4.9 × 10 -4 M

D. 3.8 × 10 -4 M

E. 1.1 × 10 -5 M

Watch Solution

The Henry's law constant (k H) for O2 in water at 20°C is 1.28 x 10 -3 mol/L•atm. How many grams of O2 will dissolve in 1.75 L of H 2O in contact with air, where the partial pressure of O2 is 1.32 atm?

A. 0.0541 g

B. 0.0473 g

C. 0.0946 g

D. 0.0270 g

E. 0.946 g

Watch Solution

All carbonated beverages are bottled under pressure because____________________

A) if the pressure is increased, the solubility of the gas will increase.

B) this will avoid the external contamination during the storage process.

C) if the pressure is increased, the solubility of the gas will decrease.

D) the pressure is necessary to keep the gas above the solution.

E) the temperature changes constantly but the gas will remain with the same solubility.

Watch Solution

The solution of nitrogen gas at 25°C and a nitrogen pressure of 522 mmHg is 4.7 x 10 -4 mol/L. What is the value of Henry's Law constant in mol/L•atm?

A. 6.8 x 10-4 mol/L • atm
B. 9.0 x 10-7  mol/L • atm
C. 1.5 x 10-4  mol/L • atm
D. 3.2 x 10-4  mol/L • atm
E. 4.7 x 10-4  mol/L • atm

 

Watch Solution

Coca-Cola took a public relations hit a few months ago when it was discovered that their “scientists” stated that obesity was due to insufficient exercise and not sugary soft drinks (New York Times, August 9, 2015). 

The partial pressure of carbon dioxide in the headspace of bottled Coke (the space above the liquid) is 3-4 atm, so let’s assume 3.5 atm. The Henry’s law constant for CO2(g) at 20°C is 3.91 x 10-2 mol/L∙atm. Calculate the solubility (mol/L) of carbon dioxide in water at 20°C.

Watch Solution

Nitrogen gas, N(g), has a certain solubility when dissolved in octane (l). In which of the following cases would the solubility of N(g) decrease?

I) lowering the temperature of the solvent

II) increasing the amount of solvent

III) reducing the pressure of N (g)

1. I and II

2. II only

3. II and III

4. I and III

5. III only

6. I only

7. I, II and III

Watch Solution

Calculate the number of moles of oxygen that will dissolve in 45 L of water at 20°C if the partial pressure of oxygen is 0.21 atm. Henry's constant for oxygen is 0.0013 mol/ L•atm

1. 0.00027 mol

2.  0.0013 mol

3. 0.012 mol

4. 0.0062 mol

5. 0.28 mol

Watch Solution

The "fizz" in a carbonated beverage is from carbon dioxide that has been dissolved in the aqueous solution. This is typically achieved by pressuring the "head space" (the empty space above the liquid in the bottle) with carbon dioxide gas. 

a. What is the concentration of CO 2 in a soda that has been pressurized with 3.0 atm of CO 2 (in molarity)? Assume a Henry's law constant of 0.0769 M/atm. 

 

 

 

 

b. How does the solubility of CO 2 in water change after it is opened and is at equilibrium with the air (i.e. does it become more or less soluble)?

Watch Solution

True or false: The Henry's Law constant for a gas should decrease with an increase in temperature. __________

Watch Solution

The solubility of N2 in blood at 37°C and a partial pressure of 0.8 atm is 5.6 x 10 ‐4 mole/L. A deep‐sea diver breathes compressed air with a partial pressure of N2 equal to 4.8 atm. Assume that the total volume of blood in the body is 5.0 L. Calculate the amount of N2 gas released (in liters at 37°C and 1.00 Atm) when the diver returns to the surface, where the partial pressure of N2 is 0.80 atm.

A) 0.356 L
B) 0.0540 L
C) 0.427 L
D) 0.342 L
E) 0.085 L

 

Watch Solution

Calculate the pressure of O2 necessary to generate an aqueous solution that is 6.0 x 10‐2 M in O 2 at 25° C. The Henry’s law constant for  O 2 in water at 25°C is 1.3 x 10 ‐3 mole/L•atm

A) 7.8 x 10‐5 atm
B) 2.1 x 10‐2 atm
C) 46 atm
D) 1.28 x 104 atm
E) none of these

 

 

 

Watch Solution

 The solubility of ammonia gas, NH 3, at 25 oC is 5.8 x 101 M/ atm. If the partial pressure of ammonia gas in air is 0.87 atm, what is the concentration (molarity) of the dissolved ammonia? 

a. 4.05 x 101 M

b. 7.68 x 101 M

c. 6.98 x 101 M

d. 5.05 x 101 M

e. 1.41 x 101

Watch Solution

Determine the Henry's law constant for ammonia in water at 25°C if an ammonia pressure of 0.022 atm produces a solution with concentration of 1.3 M.

A) 59 M/atm

B) 0.017 M/atm

C) 0.029 M/atm

D) 35 M/atm

E) 0.038 M/atm

Watch Solution

The solubility of oxygen in lakes in the Rocky Mountains is affected by the altitude. If the solubility of O2 from the air is 2.67 x 10-4 M at sea level and 25°C, what is the solubility of O 2 at an elevation of 12,000 ft where the atmospheric pressure is 0.657 atm? Assume the temperature is 25°C, and that the mole fraction of Oin air is 0.209 at both 12,000 ft and at sea level.

A) 1.75 x 10-4 M

B) 2.67 x 10-4 M

C) 3.66 x 10-4 M

D)4.06 x 10-4 M

E) none of the above

Watch Solution

Calculate the mass of nitrogen (in g) dissolved at room temperature in 50 L of water. The atmospheric pressure is 1.3 atm. Assume that the mole fraction of nitrogen is 0.78 in air and the Henry's law constant for nitrogen in water at this temperature is 6.1 x 10-4 M/atm.

A. 0.019 g

B. 0.017 g

C. 0.865 g

D. 0.433 g

E. 8.65 x 10-3 g

Watch Solution

At what pressure will the solubility of carbon monoxide (CO) gas be 1.26 x 10  -1 g/L at 25 oC? The Henry's Law constant for carbon monoxide at 25 oC is 3.40 x 10-2 M/atm

A. 3.71 atm
B. 0.132 atm
C. 7.56 atm
D. 0.270 atm
E. 1.53 x 10-4 atm

Watch Solution

The solubility of an uknown gas at 1.28 atm is 0.528 mg/mL. Calculate the pressure at which the solubility of the gas is 0.367 mg/mL.

a. 0.151 atm

b. 0.889 atm

c. 1.12 atm

d. 0.248 atm

e. 1.84 atm

Watch Solution

Henry's law constant for dissolved oxygen in water is k = 1.2 x 10  -3 M•atm-1. Suppose you could buy a bottle of water claiming that it contains 72 ppm oxygen. What pressure would the water have to be bottled under to obtain the claimed concentration?

a. 60.0 atm

b. 0.063 atm

c. 3.68 atm

d. 1.88 atm

e. 1.61 atm

 

Watch Solution

Determine the solubility of Nin water exposed to air at 25°C if the atmospheric pressure is 1.2 atm. Assume that the mole fraction of nitrogen is 0.78 in air and the Henry's law constant for nitrogen in water at this temperature is 6.1 x 10-4 M/atm.

A. 1.5 x 10-4 M

B. 6.5 x 10-4 M

C. 5.7 x 10-4 M

D. 1.8 x 10-4 M

E. 3.6 x 10-4 M

Watch Solution

Calculate the number of grams of nitrogen gas that will dissolve in 125 L of water if the partial pressure of the nitrogen gas is 0.79 atm. Henry’s law constant for nitrogen gas is 0.00060 M/atm.

A. 0.83 g

B. 1.7 g

C. 0.00047 g

D. 0.059 g

Watch Solution

Why is it that the contents of a bottle of soda opened at room temperature tend to expand all over the persons hand’s holding the bottle, but the same bottle if opened when chilled just makes a slight hissing sound?

1. The carbon dioxide gas intentionally dissolved in the soda is more soluble at lower temperatures.

2. The bottle allows more gas to expand through the pores of the plastic at lower temperatures.

3. The bottle shrinks at low temperatures, creating less headspace for the gas above the soda, which means more gas dissolves in it, so less escapes when the bottle is opened.

4. The nitrogen gas intentionally dissolved in the soda is more soluble at lower temperatures.

Watch Solution

A mixture of gases contains 7.5 g H 2 and 29.6 g N 2 with a total pressure of 525 torr.

Calculate the solubility of nitrogen gas if its Henry’s constant is 6.1 x 10  –4 M/atm. 

Watch Solution

In general, as the temperature increases, the solubility of gas in a given liquid ________________, and the solubility of most solids in a given liquid ________________

  1. Increases, increases
  2. Increases, decreases
  3. Decreases, increases
  4. Decreases, decreases
Watch Solution

In deep sea diving, nitrogen is dissolved in the bloodstream under the high pressure. This leads to the condition known as “the bends.” Actually, nitrogen is much more soluble in fatty tissue than it is aqueous solutions (e.g. blood), and the nitrogen dissolved in the brain at a higher pressure can be a great concern for divers.

 

The Henry’s law constant for N2(g) in fatty tissue is around 2 x 10-3 mol/L•atm at 25°C (as opposed to 6.8 x 10-4 mol/L•atm in water at that same temperature). Calculate the concentration of N2(g) in fatty tissue if the air pressure is 2.5 atm (that would correspond to a depth of about 50 feet). Remember the air is roughly 79% nitrogen.

Watch Solution

Recently, I was given laughing gas (N 2O, MW = 44.013 g/mol) during some dental work. They did this by applying a tube over my nose and flowing N2O into the tube, increasing the partial pressure of N2O to 0.4 atm. If the concentration of N2O in my blood after the dental procedure was 1.25 x 10-3 M, calculate the Henry's law constant for N2O.

Watch Solution

The solubility of CO2 in water at 25 °C and 1 atm is 0.034 mol/L. What is its solubility under atmospheric conditions where the partial pressure of CO2  is 0.003 atm? 

Watch Solution

Fish breathe the dissolved air in water through their gills. Assuming the partial pressures of Nand O2 in air to be 0.80 atm and 0.20 atm, respectively, calculate the concentrations of oxygen and nitrogen in water at 298 K. Henry’s law constant for N2 (g) and O2 (g) in water at 298 K are 6.8 x 10-4 and 1.3 x 10-3 mol L-1 atm-1, respectively.

Watch Solution

Calculate the mass of oxygen (in mg) dissolved in a 5.00 L bucket of water exposed to a pressure of 1.13 atm of air.  Assume the mole fraction of oxygen in air to be 0.21 and the Henryʹs law constant for oxygen in water at this temperature to be 1.3 × 10 -3 M/atm.

A) 23.5 mg      B) 27.3 mg      C) 49.4 mg      D) 13.7 mg      E) 47.0 mg

Watch Solution

Determine the partial pressure of oxygen necessary to form an aqueous solution that is 4.1 × 10–4 M O2 at 25°C. The Henry's law constant for oxygen in water at 25°C is 1.3 × 10 –3.

A. 0.53 atm

B. 0.24 atm

C. 0.32 atm

D.1.9 atm

E. 0.77 atm

Watch Solution

As temperature increases, solubility of a solid in liquid generally ____________ while solubility of a gas in liquid generally ______________.

A. Increases; Decreases

B. Increases; Increases

C. Decreases; Increases

D. Decreases; Decreases

Watch Solution

Perfluorinated compounds are hydrocarbons where most or all of the hydrogens have been replaced by fluorine atoms. Perfluorinated solvents have a number of interesting and exploitable properties. For example, oxygen is very soluble in perfluorinated solvents. and they have been investigated as temporary means of supplying oxygen in the case of very premature births before the lungs are fully developed. The Henry's law constant for C7F14 is 2.5 x 10-2 mol/L•atm at 25°C, roughly ten times greater than the Henry's law constant for water at that temperature.

 

A. Calculate the concentration in M of oxygen dissolved in C 7F14 exposed to air at 25°C. Air is 21% oxygen.

 

 

 

 

 

B. The concentration of oxygen in the umbilical vein is in the neighborhood of 20 mg/100 mL of blood. Convert your answer from Part A to mg/100 mL

Watch Solution

Henry's Law constants (K) are the equilibrium constants for the reaction of a gas dissolving in a liquid; X(g)→X(aq). Which of the following should have the largest Henry's Law constant for dissolving in water?

a. CO2

b. He

c. Ar

d. N2

e. NH3

Watch Solution