Quantitative Chemistry C3 Flashcards
What is relative formula mass?
Relative formula mass (M_r) is the sum of the relative atomic masses of all the atoms in a molecular formula.
How do you find the relative formula mass of MgCl2?
1) Look up the relative atomic masses: A of Mg = 24, A of Cl = 35.5.
2) Calculate: M_r = 24 + (2 x 35.5) = 95.
How do you calculate the percentage mass of an element in a compound?
Percentage mass = (A x number of atoms of that element / M_r of the compound) x 100.
What is the percentage mass of sodium in sodium carbonate (Na2CO3)?
M_r of Na2CO3 = (2 x 23) + 12 + (3 x 16) = 106.
Percentage mass of sodium = (23 x 2 / 106) x 100.
How do you find the mass of iron in a mixture containing 20% iron ions?
In a 50 g mixture, the mass of iron = 50 x 0.20 = 10 g.
How do you calculate the percentage mass of iron in iron chloride (FeCl3)?
M_r of FeCl3 = 56 + (3 x 35.5) = 142.5.
Percentage mass of iron = (56 / 142.5) x 100 = 39.44%.
What is the relative atomic mass (A) of an element?
The relative atomic mass is the same as its mass number and can be found on the periodic table.
How much iron chloride is needed to provide 10 g of iron in a mixture?
To provide 10 g of iron, you need to calculate the mass of iron chloride based on its percentage mass of iron.
What is the percentage composition by mass of potassium in potassium hydroxide (KOH)?
Calculate using the formula: (A of K / M_r of KOH) x 100.
What is a mole?
A mole is simply the name given to an amount of a substance, similar to how ‘a million’ represents 1,000,000.
The Avogadro constant is 6.02 x 10^23.
How many particles are in one mole?
One mole of any substance contains Avogadro’s number of particles, which is 6.02 x 10^23. The particles could be atoms, molecules, ions, or electrons.
What is the relationship between moles and mass?
The mass of one mole of atoms or molecules of any substance is equal to the relative atomic mass (A_r) or relative formula mass (M_r) of that substance in grams.
What is the mass of one mole of carbon?
One mole of carbon has a relative atomic mass (A_r) of 12 g.
What is the mass of one mole of nitrogen gas (N2)?
One mole of nitrogen gas (N2) has a relative formula mass (M_r) of 28 g (2 x 14).
What is the mass of one mole of carbon dioxide (CO2)?
One mole of carbon dioxide (CO2) has a relative formula mass (M_r) of 44 g (12 + [2 x 16]).
How do you calculate the number of moles from mass?
Number of moles = mass in grams (of an element or compound) / M_r (of the element or compound).
How many moles are in 66 g of carbon dioxide (CO2)?
To find the number of moles in 66 g of CO2, use the formula: 66 g / 44 g/mol = 1.5 mol.
What is the mass of 4 moles of carbon?
The mass of 4 moles of carbon is 4 x 12 g = 48 g.
What is the formula triangle for calculating moles?
The formula triangle is: M = mass / number of moles. Cover the variable you want to find.
What is a common misconception about moles?
Calculations involving moles can be confusing, but they don’t need to be. Understanding the basics can help alleviate the confusion.
What is the Conservation of Mass?
You can’t create or destroy matter; mass is always conserved in chemical reactions.
What happens to atoms during a chemical reaction?
No atoms are destroyed and no atoms are created.
What can be said about the number and types of atoms in a reaction equation?
The same number and types of atoms are present on each side of a reaction equation.
What does it mean when mass is conserved?
No mass is lost or gained during a chemical reaction.
How can you show that mass is conserved in a reaction?
By adding up the relative formula masses of the substances on each side of a balanced equation.
Example of mass conservation in a reaction: 2Li + F2 → 2LiF.
Total mass of reactants equals total mass of products: 52 = 52.
What happens if the mass seems to change during a reaction?
Usually, a gas is involved.
What does it indicate if the mass increases during a reaction?
It likely means one of the reactants is a gas from the air.
What happens when a gas reacts and is contained in a reaction vessel?
The total mass inside the vessel increases as the gas is now accounted for.
What does it indicate if the mass decreases during a reaction?
It likely means one of the products is a gas that escapes the reaction vessel.
What happens when a metal carbonate decomposes?
The mass of the reaction vessel decreases if it’s not sealed, but the total mass of products equals the mass of the reactants.
What is a key takeaway about mass in reactions?
The total mass of reactants is always equal to the total mass of products.
What is concentration in chemistry?
Concentration is the amount of a substance (e.g. mass or number of moles) in a certain volume of a solution.
How does the amount of solute affect concentration?
The more solute there is in a given volume, the more concentrated the solution.
What are the units for measuring concentration?
Concentration can be measured in g/dm³.
How do you calculate concentration in g/dm³?
Concentration = mass of solute / volume of solvent in dm³.
What is the concentration of a solution with 30 g of sodium chloride in 0.2 dm³ of water?
The concentration is 150 g/dm³.
How do you convert cm³ to dm³?
1 dm³ = 1000 cm³.
What is the concentration of a solution with 15 g of salt in 500 cm³?
First, convert 500 cm³ to dm³: 500 cm³ = 0.5 dm³. Then, concentration = 15 g / 0.5 dm³ = 30 g/dm³.
How can you find the mass of solute if you know its concentration?
Use the formula: mass = concentration x volume.
What mass of salt is needed to create a solution with a concentration of 24 g/dm³ in 0.40 dm³ of water?
mass = 24 g/dm³ x 0.40 dm³ = 9.6 g.
What should you remember about measurements?
All measurements have some uncertainty.
