0.9 Quantitative aspects of chemical change  (Page 8/10)

Using the combined gas law

1. An enclosed gas(i.e. one in a sealed container) has a volume of $300\mathrm{cm}{}^3$ and a temperature of $300\mathrm{K}$ . The pressure of the gas is $50\mathrm{kPa}$ . Calculate the number of moles of gas that are present in the container.
   
2. What pressure will $3\mathrm{mol}$ of gaseous nitrogen exert if it is pumped into a container that has a volume of $25\mathrm{dm}{}^3$ at a temperature of $29{}^0\mathrm{C}$ ?
   
3. The volume of air inside a tyre is 19 litres and the temperature is $290\mathrm{K}$ . You check the pressure of your tyres and find that the pressure is $190\mathrm{kPa}$ . 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 $310\mathrm{K}$ and the number of moles of gas is $13\mathrm{mols}$ 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.

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

Concentration

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

Molarity and the concentration of solutions

1. $\mathrm{5,95}\mathrm{g}$ of potassium bromide was dissolved in $400{\mathrm{cm}}^3$ of water. Calculate its molarity.
   
2. $100\mathrm{g}$ of sodium chloride (NaCl) is dissolved in $450{\mathrm{cm}}^3$ of water.
   1. How many moles of NaCl are present in solution?
   2. What is the volume of water (in ${\mathrm{dm}}^3$ )?
   3. Calculate the concentration of the solution.
   4. What mass of sodium chloride would need to be added for the concentration to become $\mathrm{5,7}\mathrm{mol}·{\mathrm{dm}}^{-3}$ ?
3. What is the molarity of the solution formed by dissolving $80\mathrm{g}$ of sodium hydroxide ( $\mathrm{NaOH}$ ) in $500{\mathrm{cm}}^3$ of water?
   
4. What mass (g) of hydrogen chloride ( $\mathrm{HCl}$ ) is needed to make up $1000{\mathrm{cm}}^3$ of a solution of concentration $1\mathrm{mol}·{\mathrm{dm}}^{-3}$ ?
   
5. How many moles of $\mathrm{H}{}_2\mathrm{SO}{}_4$ are there in $250{\mathrm{cm}}^3$ of a $\mathrm{0,8}\mathrm{M}$ sulphuric acid solution? What mass of acid is in this solution?