C3 - Quantitative Chemistry Flashcards
What is the definition of a mole?
A mole is simply the name given to an amount of a substance.
What does the mass of one mole of atoms or molecules equal?
The mass in grams is equal to the relative atomic mass (A) or relative formula mass (M) of the element or compound.
What is the mass of one mole of carbon?
12 g.
What is the mass of one mole of nitrogen gas (N₂)?
28 g.
What is the mass of one mole of carbon dioxide (CO₂)?
44 g.
How many particles are contained in one mole of any substance?
6.023 x 10²³ atoms or molecules.
What is the formula to calculate the number of moles in a given mass?
Number of moles = mass in g (of an element or compound) ÷ M (of the element or compound).
Calculate the number of moles in 66 g of carbon dioxide (CO₂).
1.5 mol.
What is the molar mass (M) of carbon dioxide (CO₂)?
44 g (12 + [2 x 16]).
What is the symbol for the unit ‘moles’?
‘mol’.
If there are 4 moles of carbon dioxide (CO₂), how many moles of carbon are present?
4 moles.
What is the mass of carbon in 4 moles of carbon dioxide (CO₂)?
48 g.
Fill in the blank: The number of moles can be rearranged using a _______ triangle.
formula.
True or False: The mole is a unit that represents a specific quantity of particles.
True.
What is the importance of the mole in chemistry?
It allows for the conversion between the mass of substances and the number of particles.
What does the formula triangle help to find?
It helps to find mass, number of moles, or molar mass.
What does ‘M’ represent in the context of moles?
Molar mass of the element or compound.
What is the relationship between moles and grams in a chemical reaction?
The number of moles of reactants and products must be conserved.
What is the principle regarding mass in a chemical reaction?
Mass is always conserved during a chemical reaction
This means no atoms are destroyed or created.
What happens to the number and types of atoms during a chemical reaction?
The number and types of atoms remain the same on each side of the reaction equation.
What does it mean when we say mass is conserved?
No mass is lost or gained during a chemical reaction.
Provide an example of a balanced equation that demonstrates conservation of mass.
2Li + F2 → 2LiF
How do you show that mass is conserved in the reaction 2Li + F2 → 2LiF?
Total mass of reactants equals total mass of products: 2 x M(Li) + 2 x M(F) = 52 and 2 x M(LiF) = 52.
What happens to mass in an unsealed reaction vessel when a gas is involved?
The mass may appear to change due to gas escaping or entering the vessel.
If the mass of a reaction vessel increases, what is one possible explanation?
One of the reactants is a gas found in air that enters the vessel.
If the mass of a reaction vessel decreases, what is a likely reason?
One of the products is a gas that escapes into the air.
In a thermal decomposition reaction, what is the relationship between the mass of the reactants and products?
The total mass of the reactants equals the total mass of the products.
Fill in the blank: In a reaction where a metal carbonate decomposes, the equation is ______.
metal carbonate(s) → metal oxide(s) + carbon dioxide(g)
True or False: A gas will expand to fill any container it’s in.
True
What happens to gas produced in a reaction if the reaction vessel is not sealed?
The gas escapes into the air around the vessel.
What is the relative formula mass of a compound?
The sum of the relative atomic masses of all the atoms in the molecular formula.
How do you find the relative formula mass of MgCl₂?
Mg + (2 × Cl) = 24 + (2 × 35.5) = 95.
What is the relative atomic mass (Aᵣ) of magnesium?
24.
What is the relative atomic mass (Aᵣ) of chlorine?
35.5.
How do you calculate the percentage mass of an element in a compound?
Percentage mass = (Aᵣ × number of atoms of that element) / Mᵣ of the compound × 100.
What is the percentage mass of sodium in sodium carbonate (Na₂CO₃)?
23 / 106 × 100 = 43%.
If a mixture contains 20% iron ions by mass, how much iron is in 50 g of the mixture?
10 g of iron.
What is the percentage mass of iron in iron chloride (FeCl₂)?
44.09%.
How much iron chloride is needed to provide 10 g of iron?
23 g of iron chloride.
Fill in the blank: The formula to calculate the percentage mass of an element in a compound is _______.
(Aᵣ × number of atoms) / Mᵣ × 100.
True or False: The relative atomic mass of an element can be found on the periodic table.
True.
What does the number of moles in a chemical reaction represent?
The number of moles indicates how many moles of each substance take part or is formed during the reaction.
In the reaction Mg(a) + 2HC(09) → MgC| (09) + 2(8), how many moles of magnesium react?
1 mole of magnesium.
In the same reaction, how many moles of hydrochloric acid are involved?
2 moles of hydrochloric acid.
What is the first step to balance equations using reacting masses?
Divide the mass of each substance by its relative formula mass to find the number of moles.
What should you do if the numbers of moles calculated are not whole numbers?
Multiply all the numbers by the same amount so that they all become whole numbers.
How do you write the balanced symbol equation for a reaction?
By putting the whole number ratios in front of the chemical formulas.
What is the relative formula mass (M) of zinc oxide (ZnO)?
81.
What is the relative formula mass (M) of carbon dioxide (CO2)?
44.
How many moles of carbon were produced when 0.60 g reacted?
0.050 mol.
What is the balanced symbol equation for the reaction involving zinc oxide and carbon?
2ZnO + C → CO2 + 2Zn.
Fill in the blank: The big numbers in front of the chemical formulas in a balanced equation indicate the number of _______.
[moles]
True or False: The little numbers in chemical formulas indicate how many moles of each element are present.
False.
What do you need to calculate the number of moles from the mass of a substance?
The relative formula mass (M) of the substance.
List the steps to balance a chemical equation using reacting masses.
- Divide the mass by M
- Divide by the smallest number of moles
- Multiply to make whole numbers
- Write the balanced equation.
What is the relative atomic mass (A) of zinc (Zn)?
65.
After calculating moles, if you get 0.10 for ZnO, what does this imply about its ratio in the balanced equation?
It will be in a ratio of 2 in the balanced equation.
What is the limiting reactant?
The reactant that’s used up in a reaction
It limits the amount of product that’s formed.
What happens to the reaction when one reactant is used up?
The reaction stops
Any remaining reactants are in excess.
How is the amount of product formed related to the limiting reactant?
Directly proportional
Halving the limiting reactant halves the product; doubling it doubles the product.
What is the first step in calculating the mass of a product formed in a reaction?
Write out the balanced equation
This is essential for stoichiometric calculations.
What is the second step in calculating the mass of a product formed?
Work out relative formula masses (M.) of the reactant and product
This helps in mole calculations.
What formula is used to calculate the number of moles?
Moles = mass / molar mass
This formula is crucial for converting mass to moles.
In the example provided, what is the balanced equation for the reaction of aluminium?
4Al + 3O2 → 2Al2O3
This equation shows the stoichiometry of the reaction.
What is the relative formula mass of aluminium oxide (Al2O3)?
102
Calculated as (2 × 27) + (3 × 16).
How many moles of aluminium are in 135 g?
5 moles
Calculated using the formula: Moles = 135 g / 27 g/mol.
What is the mole ratio of aluminium to aluminium oxide in the reaction?
4 moles of Al react to produce 2 moles of Al2O3
This indicates that half the number of moles of aluminium oxide is produced.
How many moles of aluminium oxide are produced from 5 moles of aluminium?
2.5 moles
This is derived from the stoichiometric ratio in the balanced equation.
What is the mass of 2.5 moles of aluminium oxide?
255 g
Calculated using mass = moles × Molar mass (2.5 × 102).
Fill in the blank: The amount of product formed is directly proportional to the amount of _______.
[limiting reactant]
True or False: Excess reactants are completely consumed in a reaction.
False
Excess reactants remain after the limiting reactant is used up.
What is concentration in the context of solutions?
The amount of a substance (e.g., mass or number of moles) in a certain volume of a solution
Concentration indicates how crowded the solute is in a solution.
What happens to the concentration of a solution as more solute is added?
The concentration increases
More solute means more crowded conditions in the solution.
How is concentration measured in g/dm³?
Concentration = mass of solute / volume of solvent in dm³
Units are expressed as grams per cubic decimeter.
Calculate the concentration of a sodium chloride solution with 30 g dissolved in 0.2 dm³ of water.
150 g/dm³
Calculation: 30 g / 0.2 dm³ = 150 g/dm³.
Convert 500 cm³ to dm³.
0.5 dm³
500 cm³ ÷ 1000 = 0.5 dm³.
What is the concentration of a solution with 15 g of salt in 500 cm³?
30 g/dm³
Calculation: Concentration = 15 g / 0.5 dm³ = 30 g/dm³.
How do you rearrange the formula for concentration to find mass?
mass = concentration x volume
This formula allows you to calculate the mass of solute needed.
What mass of salt is needed to achieve a concentration of 24 g/dm³ in 0.40 dm³ of water?
9.6 g
Calculation: mass = 24 g/dm³ x 0.40 dm³ = 9.6 g.
Fill in the blank: Concentration can be measured in _______.
g/dm³
This is a common unit for measuring concentration in solutions.
True or False: The concentration of a solution decreases as more solute is added.
False
More solute increases the concentration of the solution.
What is the formula to calculate concentration?
Concentration = mass of solute / volume of solvent
This formula is essential for determining the concentration of solutions.
