5.95 g of potassium bromide was dissolved in 400 cm
of water. Calculate its molarity.
100 g of sodium chloride (NaCl) is dissolved in 450 cm
of water.
How many moles of NaCl are present in solution?
What is the volume of water (in dm
)?
Calculate the concentration of the solution.
What mass of sodium chloride would need to be added for the concentration to become 5.7 mol.dm
?
What is the molarity of the solution formed by dissolving 80 g of sodium hydroxide (NaOH) in 500 cm
of water?
What mass (g) of hydrogen chloride (HCl) is needed to make up 1000 cm
of a solution of concentration 1 mol.dm
?
How many moles of H
SO
are there in 250 cm
of a 0.8M sulphuric acid solution? What mass of acid is in this solution?
Stoichiometric calculations
Stoichiometry is the calculation of the quantities of reactants and products in chemical reactions. It is also the numerical relationship between reactants and products. The Grade 10 discussion on representing chemical changeshowed how to write balanced chemical equations. By knowing the ratios of substances in a reaction, it is possible to use stoichiometry to calculate the amount of either reactants or products that are involved in the reaction. The examples shown below will make this concept clearer.
Khan academy video on stoichiometry - 1
What volume of oxygen at S.T.P. is needed for the complete combustion of 2dm
of propane (C
H
)? (Hint: CO
and H
O are the products in this reaction (and in all combustion reactions))
From the balanced equation, the ratio of oxygen to propane in the reactants is 5:1.
1 volume of propane needs 5 volumes of oxygen, therefore 2 dm
of propane will need 10 dm
of oxygen for the reaction to proceed to completion.
A closer look at the previous worked example shows that 5.6 g of iron is needed to produce 8.79 g of iron (II) sulfide. The amount of sulfur that is needed in the reactants is 3.2 g. What would happen if the amount of sulfur in the reactants was increased to 6.4 g but the amount of iron was still 5.6 g? Would more FeS be produced? In fact, the amount of iron(II) sulfide produced remains the same. No matter how much sulfur is added to the system, the amount of iron (II) sulfide will not increase because there is not enough iron to react with the additional sulfur in the reactants to produce more FeS. When all the iron is used up the reaction stops. In this example, the iron is called the
limiting reagent . Because there is more sulfur than can be used up in the reaction, it is called the
excess reagent .
Questions & Answers
if three forces F1.f2 .f3 act at a point on a Cartesian plane in the daigram .....so if the question says write down the x and y components ..... I really don't understand
a fixed gas of a mass is held at standard pressure temperature of 15 degrees Celsius .Calculate the temperature of the gas in Celsius if the pressure is changed to 2×10 to the power 4
