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The standard units used for this equation are P in Pa, V in m 3 and T in K. Remember also that 1000cm 3 = 1dm 3 and 1000dm 3 = 1m 3 .

A sample of gas occupies a volume of 20 dm 3 , has a temperature of 280 K and has a pressure of 105 Pa. Calculate the number of moles of gas that are present in the sample.

  1. The only value that is not in SI units is volume. V = 0.02 m 3 .

  2. We know that pV = nRT


    n = p V R T
  3. n = 105 × 0 . 02 8 . 31 × 280 = 2 . 1 2326 . 8 = 0 . 0009 moles
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Using the combined gas law

  1. An enclosed gas(i.e. one in a sealed container) has a volume of 300 cm 3 and a temperature of 300 K. The pressure of the gas is 50 kPa. Calculate the number of moles of gas that are present in the container.
  2. What pressure will 3 mol of gaseous nitrogen exert if it is pumped into a container that has a volume of 25 dm 3 at a temperature of 29 0 C?
  3. The volume of air inside a tyre is 19 litres and the temperature is 290 K. You check the pressure of your tyres and find that the pressure is 190 kPa. How many moles of air are present in the tyre?
  4. Compressed carbon dioxide is contained within a gas cylinder at a pressure of 700 kPa. The temperature of the gas in the cylinder is 310 K and the number of moles of gas is 13 moles of carbon dioxide. What is the volume of the gas inside the cylinder?

Molar concentrations of liquids

A typical solution is made by dissolving some solid substance in a liquid. The amount of substance that is dissolved in a given volume of liquid is known as the concentration of the liquid. Mathematically, concentration (C) is defined as moles of solute (n) per unit volume (V) of solution.

C = n V

For this equation, the units for volume are dm 3 . Therefore, the unit of concentration is mol. dm - 3 . When concentration is expressed in mol. dm - 3 it is known as the molarity (M) of the solution. Molarity is the most common expression for concentration.

Do not confuse molarity (M) with molar mass (M). Look carefully at the question in which the M appears to determine whether it is concentration or molar mass.

Concentration is a measure of the amount of solute that is dissolved in a given volume of liquid. It is measured in mol.dm - 3 . Another term that is used for concentration is molarity (M)

If 3.5 g of sodium hydroxide (NaOH) is dissolved in 2.5 dm 3 of water, what is the concentration of the solution in mol. dm - 3 ?

  1. n = m M = 3 . 5 40 = 0 . 0875 m o l
  2. C = n V = 0 . 0875 2 . 5 = 0 . 035

    The concentration of the solution is 0.035 mol.dm - 3 or 0.035 M

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You have a 1 dm 3 container in which to prepare a solution of potassium permanganate (KMnO 4 ). What mass of KMnO 4 is needed to make a solution with a concentration of 0.2 M?

  1. C = n V


    n = C × V = 0 . 2 × 1 = 0 . 2 m o l
  2. m = n × M = 0 . 2 × 158 . 04 = 31 . 61 g

    The mass of KMnO 4 that is needed is 31.61 g.

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How much sodium chloride (in g) will one need to prepare 500 cm 3 of solution with a concentration of 0.01 M?

  1. V = 500 1000 = 0 . 5 d m 3
  2. n = C × V = 0 . 01 × 0 . 5 = 0 . 005 m o l
  3. m = n × M = 0 . 005 × 58 . 45 = 0 . 29 g

    The mass of sodium chloride needed is 0.29 g

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Questions & Answers

what diference vector ans scalar
Khayalethu Reply
what is newtons first law basically about?
Think about it like this: Okay so you're in a car right and it's going straight right? The car then suddenly takes a sharp right turn, have you noticed that your body resists going to the right, so it kinda goes in the opposite direction /the direction the car was originally going in.
This is called inertia so your body is resisting the change in its motion.
So basically newton's first law states that and object will CONTINUE in its state of rest/uniform velocity in a straight line unless it is acted upon by a resultant force.
it resist the change occuring in the body.
how do you calculate the angle of incidence ?
Thabisa Reply
what happen when a ray light of energy is converted into another form of energy
Hansromy Reply
how do you run the demo?
Lauren Reply
what is a covalent bond
Mbuso Reply
what angle does atoms bond at when it is a trigonal planar shape
Olebogeng Reply
what is the graph of acceleration vs force?
Kgothatso Reply
investigate the relationship between force and acceleration
Hlumelo Reply
Aim : investigate the relationship between force and acceleration
The relationship between force and direction is directly proportional, which means that when force increases acceleration increases and if it decreases so does acceleration
Law of Acceleration - The acceleration of an object is directly proportional to the force acting on it and inversely proportional to the mass of the object.
how to calculate frictional force
Esesethu Reply
frictional force =to the parallel component of weight Fgsin
What are the effects of Intermolecular forces
Mpho Reply
what is meant by the term induced momentary dipole
Lucky Reply
induced means forced so in this type of a intermolecular force a dipole is forced
What is the difference between acceleration and force
Fanini Reply
what is the definition of bond length
Mmabophelo Reply
Bond length is the average distance between the nuclei of 2 bonded atoms
ask would you calculate coefficient
Ashley Reply
can a bond be polar and the molecule be a non polar?
Siyanda Reply

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Source:  OpenStax, Siyavula textbooks: grade 11 physical science. OpenStax CNX. Jul 29, 2011 Download for free at http://cnx.org/content/col11241/1.2
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