It is important to be able to quantify the changes that take place during a chemical reaction.
The
mole (n) is a SI unit that is used to describe an amount of substance that contains the same number of particles as there are atoms in
of carbon.
The number of particles in a mole is called the
Avogadro constant and its value is
. These particles could be atoms, molecules or other particle units, depending on the substance.
The
molar mass (M) is the mass of one mole of a substance and is measured in grams per mole or
. The numerical value of an element's molar mass is the same as its relative atomic mass. For a compound, the molar mass has the same numerical value as the molecular mass of that compound.
The relationship between moles (n), mass in grams (m) and molar mass (M) is defined by the following equation:
In a balanced chemical equation, the number in front of the chemical symbols describes the
mole ratio of the reactants and products.
The
empirical formula of a compound is an expression of the relative number of each type of atom in the compound.
The
molecular formula of a compound describes the actual number of atoms of each element in a molecule of the compound.
The formula of a substance can be used to calculate the
percentage by mass that each element contributes to the compound.
The
percentage composition of a substance can be used to deduce its chemical formula.
One mole of gas occupies a volume of
.
The
concentration of a solution can be calculated using the following equation,
where C is the concentration (in
), n is the number of moles of solute dissolved in the solution and V is the volume of the solution (in
).
Molarity is a measure of the concentration of a solution, and its units are
.
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 theoretical yield of a reaction is the maximum amount of product that we expect to get out of a reaction
End of chapter exercises
Write only the word/term for each of the following descriptions:
the mass of one mole of a substance
the number of particles in one mole of a substance
Multiple choice: Choose the one correct answer from those given.
of magnesium chloride is formed as the product of a chemical reaction. Select the
true statement from the answers below:
0.08 moles of magnesium chloride are formed in the reaction
the number of atoms of
in the product is
the number of atoms of
is 0,05
the atomic ratio of
atoms to
atoms in the product is 1:1
2 moles of oxygen gas react with hydrogen. What is the mass of oxygen in the reactants?
32 g
0,125 g
64 g
0,063 g
In the compound potassium sulphate (
), oxygen makes up x% of the mass of the compound. x = ...
36.8
9,2
4
18,3
The molarity of a
solution, containing 5 g of
is...
Calculate the number of moles in:
5 g of methane (
)
3,4 g of hydrochloric acid
6,2 g of potassium permanganate (
)
4 g of neon
9,6 kg of titanium tetrachloride (
)
Calculate the mass of:
0,2 mols of potassium hydroxide (
)
0,47 mols of nitrogen dioxide
5,2 mols of helium
0,05 mols of copper (II) chloride (
)
molecules of carbon monoxide (
)
Calculate the percentage that each element contributes to the overall mass of:
Chloro-benzene (
)
Lithium hydroxide (
)
CFC's (chlorofluorocarbons) are one of the gases that contribute to the depletion of the ozone layer. A chemist analysed a CFC and found that it contained 58,64% chlorine, 31,43% fluorine and 9,93% carbon. What is the empirical formula?
14 g of nitrogen combines with oxygen to form 46 g of a nitrogen oxide. Use this information to work out the formula of the oxide.
Iodine can exist as one of three oxides (
). A chemist has produced one of these oxides and wishes to know which one they have. If he started with 508 g of iodine and formed 652 g of the oxide, which form has he produced?
A fluorinated hydrocarbon (a hydrocarbon is a chemical compound containing hydrogen and carbon.) was analysed and found to contain 8,57% H, 51,05% C and 40,38% F.
What is its empirical formula?
What is the molecular formula if the molar mass is
?
Copper sulphate crystals often include water. A chemist is trying to determine the number of moles of water in the copper sulphate crystals. She weighs out 3 g of copper sulphate and heats this. After heating, she finds that the mass is 1,9 g. What is the number of moles of water in the crystals? (Copper sulphate is represented by
).
of a
solution of sulphuric acid is added to
of a
solution of sodium hydroxide.
Write down a balanced equation for the reaction which takes place when these two solutions are mixed.
Calculate the number of moles of sulphuric acid which were added to the sodium hydroxide solution.
Is the number of moles of sulphuric acid enough to fully neutralise the sodium hydroxide solution? Support your answer by showing all relevant calculations.
(IEB Paper 2 2004)
A learner is asked to make
of sodium hydroxide (
) solution of concentration
.
Determine the mass of sodium hydroxide pellets he needs to use to do this.
Using an accurate balance the learner accurately measures the correct mass of the
pellets. To the pellets he now adds exactly
of pure water. Will his solution have the correct concentration? Explain your answer.
The learner then takes
of a
solution of sulphuric acid (
) and adds it to
of a
solution of
at
.
Write down a balanced equation for the reaction which takes place when these two solutions are mixed.
Calculate the number of moles of
which were added to the NaOH solution.
Is the number of moles of
calculated in the previous question enough to fully neutralise the
solution? Support your answer by showing all the relevant calculations.
(IEB Paper 2, 2004)
Questions & Answers
A golfer on a fairway is 70 m away from the green, which sits below the level of the fairway by 20 m. If the golfer hits the ball at an angle of 40° with an initial speed of 20 m/s, how close to the green does she come?
A mouse of mass 200 g falls 100 m down a vertical mine shaft and lands at the bottom with a speed of 8.0 m/s. During its fall, how much work is done on the mouse by air resistance
Chemistry is a branch of science that deals with the study of matter,it composition,it structure and the changes it undergoes
Adjei
please, I'm a physics student and I need help in physics
Adjanou
chemistry could also be understood like the sexual attraction/repulsion of the male and female elements. the reaction varies depending on the energy differences of each given gender. + masculine -female.
Pedro
A ball is thrown straight up.it passes a 2.0m high window 7.50 m off the ground on it path up and takes 1.30 s to go past the window.what was the ball initial velocity
2. A sled plus passenger with total mass 50 kg is pulled 20 m across the snow (0.20) at constant velocity by a force directed 25° above the horizontal. Calculate (a) the work of the applied force, (b) the work of friction, and (c) the total work.
you have been hired as an espert witness in a court case involving an automobile accident. the accident involved car A of mass 1500kg which crashed into stationary car B of mass 1100kg. the driver of car A applied his brakes 15 m before he skidded and crashed into car B. after the collision, car A s
can someone explain to me, an ignorant high school student, why the trend of the graph doesn't follow the fact that the higher frequency a sound wave is, the more power it is, hence, making me think the phons output would follow this general trend?
Nevermind i just realied that the graph is the phons output for a person with normal hearing and not just the phons output of the sound waves power, I should read the entire thing next time
Joseph
Follow up question, does anyone know where I can find a graph that accuretly depicts the actual relative "power" output of sound over its frequency instead of just humans hearing
Joseph
"Generation of electrical energy from sound energy | IEEE Conference Publication | IEEE Xplore" ***ieeexplore.ieee.org/document/7150687?reload=true
A string is 3.00 m long with a mass of 5.00 g. The string is held taut with a tension of 500.00 N applied to the string. A pulse is sent down the string. How long does it take the pulse to travel the 3.00 m of the string?