QUEENSLAND CHEMISTRY

CHAPTER 24 EXPLORING EARTH’S OCEANS
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QUESTIONS24.2 Scuba science

  1. A sample of nitrogen occupies 90.0mL at 40.0°C and a pressure of 80.0kPa. What pressure would be needed to reduce the volume to 30.0mL at 40.0°C?
  2. What would be the volume of a sample of air in a syringe at a pressure of 45.0kPa if the same sample occupied 140mL at 100kPa?
  3. A balloon has a volume of 1.5L at 1atm pressure and 24°C. Calculate its volume if it is taken outside and the temperature is –5°C.
  4. An 80L scuba tank contains 2.5mol of nitrogen. The gas is divided equally into two smaller cylinders, each having a volume of 40L. All cylinders are at the same temperature and pressure.

(a)What amount, in moles, of nitrogen is in each cylinder?

(b)What is the mass of nitrogen in each cylinder?

24.3 Pressure, temperature and volume

  1. A cylinder of compressed oxygen at 25.0°C has a volume of 50.0L and stores the oxygen at 14atm. If the cylinder needs to be cooled until the pressure falls to 10.0atm, to what temperature must it be cooled?
  2. A fitter and turner needs a supply of 450L of oxygen at 145kPa pressure and a temperature of about 30°C for a day’s work. To what pressure must her 60.0L tank be filled at 12.5°C?
  3. The observation that molar volumes are not exactly the same for all gases suggests that they do not behave exactly according to the kinetic molecular theory. Re-examine the points of this theory and identify any that may account for the reality of gas behaviour.
  4. Calculate the amount of nitrogen gas in 3.4L at SLC.
  5. 1.50L of H2S was collected at STP. Calculate the mass of hydrogen sulfide.
  6. Calculate the amount of gas in a 55L cylinder if the pressure is 360000Pa at 25°C.
  7. Calculate the mass of helium in a 100L balloon at a pressure of 0.4atm and a temperature of–5°C.
  8. What volume of ethyne gas would be produced at 25°C and 1atm, along with calcium hydroxide Ca(OH)2, from 5g of water reacting with excess carbon carbide (CaC2)?
  9. Calculate the volume of carbon dioxide at SLC that is required to produce 1.0g of glucose (C6H12O6) by photosynthesis.

Review questions

  1. When a diver breathes in all she can at sea level (atmospheric pressure=101kPa), her lung capacity is 5.85L. Calculate the volume of her lungs when she holds her breath and dives down to where the pressure is doubled. Assume the temperature is the same in the water as the air temperature.
  2. A 100mL capacity syringe contains 87mL of air measured at 101.3kPa and 25°C. To what temperature could the air be raised before its volume exceeded the syringe’s capacity?
  3. Two cylinders of oxygen are at the same temperature and pressure. The first has a volume of 20000L. A second cylinder has a volume of 500L and contains 35mol of oxygen. Calculate the mass of oxygen that must be in the first cylinder.
  4. A container of gas has a volume of 15.5L and is at a pressure of 2.00atm at 30.0°C. What size container would be needed for the same amount of gas at a pressure of 4.50atm at22.5°C?
  5. Calculate the volume occupied by 1.8mol of hydrogen at STP.
  6. 0.96L of a gas collected at STP has a mass of 5.40g. Find the molar mass of the gas.
  7. What is the pressure in a 10.0L flask at 15°C if it contains 0.30mol of nitrogen gas?
  8. You want to produce 2 L of hydrogen gas to fill a balloon at atmospheric pressure and 20°C from the reaction of hydrochloric acid with magnesium. What mass of magnesium would be needed?
  9. A sealed gas syringe has its volume doubled by drawing out the plunger. Meanwhile, its temperature is raised from 10 to 20°C. How does the new pressure compare to the old?

AIt is the same.

BIt is double.

CIt is half.

DIt is less than half.

  1. The pressure on a fixed mass of gas is doubled and at the same time the absolute temperature is doubled. The final volume is:

Aone-quarter the original volume.

Bthe same as the original volume.

Cdouble the original volume.

Dfour times the original volume.

  1. The pressure of the gas inside a scuba diver’s lungs changes from 80kPa to 120kPa. If the diver’s lungs initially held 9L of gas, their volume at this depth would be:

A3L.

B4L.

C6L.

D9L.

  1. A rigid steel drum holds a fixed volume of gas at a certain temperature and pressure. In order to halve the pressure of the gas inside the container, you could:

Ahalve the amount of gas in the container.

Bhalve the amount of gas, but double the absolute temperature.

Cdouble the amount of gas and double the absolute temperature.

Ddouble the absolute temperature.

  1. Two litres of helium gas were measured at a temperature of 400K and a pressure of 0.5atm. If the temperature of the molecules is doubled while the pressure remains constant, what volume will the gas occupy?

A0.5L

B1L

C2L

D4L

  1. A gas, originally at 100mL at 27ºC and 1.2atm, expands to 105mL at 1.65atm. The new temperature is:

A360ºC.

B87ºC.

C187ºC.

D160ºC.

  1. A gas is trapped in a syringe with a heavy mass maintaining pressure on it. Its volume does notincrease when:

Athe amount of gas in the syringe is increased.

Bthe syringe is heated.

Cthe gas is changed to a different gas of different molar mass.

Datmospheric pressure is suddenly decreased.

  1. A gas in a sealed 2L flask is at 20ºC and 101.3kPa. When the gas is heated to 50ºC, the pressure inside will be:

A405.2kPa.

B202.6kPa.

C111.7kPa.

D94.8kPa.

  1. An element is said to exist in the gaseous state. This means that:

Aits boiling point is below 0K.

Bits molecules are close together and fast moving.

Cit can be liquefied by increasing the pressure on it.

Dits molecular volume at 0ºC and 101.3kPa is 22.4L.

  1. The volume of gas in a free-moving glass syringe is increased from 100mL to 110mL by increasing the:

Apressure from 100kPa to 110kPa.

Btemperature from 20ºC to 22ºC.

Ctemperature from 300K to 330K.

Dpressure and decreasing the temperature.

  1. Molar volume at 25ºC is:

Athe volume of one mole of the gas.

Bthe volume of one molecule of the gas.

C22.4L for all gases.

Ddifferent for each different gas.

  1. 3.6g of a gas occupied 2.0L at 298K and 101.3kPa. This gas is:

Ahydrogen (H2).

Bsulfur dioxide (SO2).

Ccarbon dioxide (CO2).

Dargon (Ar).

  1. Two sealed flasks have identical volumes, are at the same temperature and contain different gases at the same pressure of 101.3kPa. The gas in flaskXhas mass 6.0g; the gas in flaskYhas mass 12.0g. It follows that:

AX contains half as many molecules as Y.

BY contains half as many molecules as X.

CX and Y contain the same number of molecules.

Dthe volume of each flask is 22.4L.

  1. Calculate the temperature of 0.4mol of gas at a pressure of 3atm and a volume of 2 L.
  2. An aerosol can of insect repellent has a volume of 120mL. The contents exert a pressure of 9.00× 102kPa at 25ºC.

(a)How many particles are present in the can of deodorant?

(b)If the contents of the can are transferred to a 300mL container, what will be the temperature if the pressure drops to 3.5× 105Pa?

  1. 4.25g of a gas occupies a volume of exactly 2.00L at STP.

(a)Calculate its density (density= ).

(b)What is its molecular mass?

  1. An evacuated 200mL flask has a mass of 84.8g. It is filled with a gas at 17.0ºC and 770mmHg pressure. The flask then weighs 85.8g. Calculate the molar mass of the gas.
  2. A gas was collected in a 1.5L glass bottle. The pressure was 1.5atm at room temperature (25ºC). The bottle was then immersed in boiling water. What quantity related to the gas would change? and by what percentage would it change?
  3. A room measures 10m×3.5m×6m. The temperature in the room is 22ºC and the pressure is 750mmHg. Ignoring the volume occupied by the furniture etc., and accepting that the air is 20% oxygen, calculate the volume of oxygen in the room if the room was atSLC.
  4. Each time Sandy breathes, she inhales about 400mL of air. Oxygen makes up about 20% by volume of air. How many oxygen molecules does she inhale in one breath at 25ºC and 1.0×104Pa?
  5. One of the reactions responsible for the brown haze in photochemical smog can be represented by the following equation.

2NO(g)+O2(g)2NO2(g)

Calculate the volume of NO2 formed from the reaction of 10mL of NO with excess O2. All volumes are measured at the same temperature and pressure.

30.An important step in the preparation of sulfuric acid involves the production of sulfur trioxide (SO3) from sulfur dioxide (SO2) and oxygen.

2SO2(g)+O2(g)2SO3(g)

(a)If all volumes are measured at the same temperature and pressure, calculate the volume of sulfur trioxide produced when 24.5mL of sulfur dioxide is placed in a container with 6.00mL of oxygen. Assume that all the SO2 and O2 that can react doesreact.

(b)Calculate the total volume of all gases remaining in the container.

31.Hydrogen reacts with oxygen in the reaction:

2H2(g)+O2(g)2H2O(g)

(a)What volume of water vapour will be produced when 4.50L of hydrogen reacts with 10.5L of oxygen?

(b)What volume of oxygen will remain unreacted?

Notes:

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