C3- Quantitative Chemistry- Paper 1 Flashcards
(35 cards)
What is the relative formula mass of a compound?
The sum of the relative atomic masses of all the atoms in the compound
It is denoted as Mr
How do you find the relative formula mass of MgCl₂?
Mg + (2 x Cl) = 24 + (2 x 36) = 96
M of MgCl₂ = 95
What is the formula to calculate the percentage mass of an element in a compound?
Percentage mass of an element = (Ar x number of atoms of that element / Mr of the compound) × 100
Ar is the relative atomic mass.
Calculate the percentage mass of sodium in sodium carbonate (Na₂CO₃) given Ar of sodium is 23, carbon is 12, and oxygen is 16.
Percentage mass of sodium = (23 x 2 / 106) × 100 = 43%
M of Na₂CO₃ = (2 × 23) + 12 + (3 × 16) = 106
If a mixture contains 20% iron ions by mass, how much iron is in 50 g of the mixture?
10 g of iron
Calculation: 50 g × 20% = 10 g
What is the percentage mass of iron in iron chloride (FeCl₂) if Ar of Fe = 56 and Ar of Cl = 35.5?
Percentage mass of iron = (56 / (56 + (2 × 35.5))) × 100 = 44.09%
M of FeCl₂ = 56 + (2 × 35.5) = 127
How much iron chloride is needed to provide 10 g of iron?
23 g of iron chloride
Calculation: 10 g of iron / 44.09% = 22.7 g, rounded to 23 g
What is the formula mass of sodium carbonate (Na₂CO₃)?
106
M of Na₂CO₃ = (2 × 23) + 12 + (3 × 16)
What is the first step to calculate the relative formula mass of a compound?
Look up the relative atomic masses of all the elements in the compound.
What is the definition of a mole?
A mole is simply the name given to an amount of a substance equivalent to 6.02 x 10^23 particles
The particles can be atoms, molecules, ions, or electrons.
What is Avogadro’s number?
6.02 x 10^23
This number represents the number of particles in one mole of a substance.
How is the mass of one mole of a substance related to its relative atomic or formula 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) in grams.
This means that the mass in grams of one mole corresponds directly to the atomic or formula mass.
What is the mass of one mole of carbon (C)?
12 g
Carbon has a relative atomic mass (A_r) of 12.
What is the mass of one mole of nitrogen gas (N2)?
28 g
Nitrogen gas has a relative formula mass (M_r) of 28 (2 x 14).
What is the mass of one mole of carbon dioxide (CO2)?
44 g
Carbon dioxide has a relative formula mass (M_r) of 44 (12 + [2 x 16]).
How do you find the number of moles in a given mass?
Number of moles = mass in g (of an element or compound) ÷ M_r (of the element or compound)
This formula calculates the amount of substance in moles based on its mass.
Calculate the number of moles in 66 g of carbon dioxide (CO2).
1.5 mol
M_r of CO2 is 44; thus, 66 g ÷ 44 g/mol = 1.5 mol.
What is the formula triangle for calculating moles?
mass = no. of moles x Mr
Covering the variable you want to find allows rearranging the formula easily.
What mass of carbon is there in 4 moles of carbon dioxide?
48 g
There are 4 moles of carbon in 4 moles of CO2, so 4 moles x 12 g/mol = 48 g.
True or False: The mass of 12 g of carbon, 28 g of N2, and 44 g of CO2 all contain the same number of particles.
True
Each of these masses represents one mole of the respective substances.
Calculate the number of moles in 90 g of water (H2O).
5 mol
M_r of H2O = 2(1) + 16 = 18; thus, 90 g ÷ 18 g/mol = 5 mol.
Calculate the mass of 0.20 mol of potassium bromide (KBr).
12 g
M_r of KBr = 39 + 80 = 119; thus, 0.20 mol x 119 g/mol = 23.8 g.
What is the principle of conservation of mass?
During a chemical reaction, mass is always conserved, meaning no atoms are destroyed or created.
In a balanced chemical equation, what is true about the number and types of atoms?
The same number and types of atoms are present on each side of the reaction equation.
