Module 2: Chapter 3 - Amount of substance Flashcards
What is a mole?
A mole is amount of any substance containing as many particles as there are carbon atoms in exactly 12g of the carbon-12 isotope (6.02x10²³ particles)
What is Avogadro’s constant, NA?
6.02x10²³ (number of particles in 1 mole of a substance)
What is the molar mass of a substance?
The mass per mole of a substance. It is the relative atomic/molecular/formula mass of a substance in g/mol
What is the equation for mass of a substance?
mass (g) = amount (mol) x Molar Mass (g/mol)
What is the amount of substance?
The quantity used for counting chemical species (atoms, molecules, ions etc), and is measured in moles
What is the unit for moles?
mol
What is hydrated?
A crystalline compound containing water molecules
What is anhydrous?
A substance that contains no water molecules
What is water of crystallisation?
Water molecules that form an essential part of the crystralline structure
CuSO₄xH₂O ( is a bullet point)
Mass of cruible (g): 18.742
Mass of crucible + hydrated salt (g): 28.726
Mass of crucible + anhydrous salt (g): 25.126
Calculate the Value of X
5
What is the 3 step method for reacting masses, gases, and solutions?
1) Convert data given into amount in moles
2) Use the mole ratio of substances to calculate amount in moles of required substance
3) Convert amount in moles back into data required
What is the empirical formula?
The simplest whole-number ratio of the atoms of each element present in a compound
What is the molecular formula?
The molecular formula shows the number and type of atoms of each element present in a molecule. It does not show how the atoms are joined together
An oxide of phosphorus contains 56.4% phosphorus and 43.6% oxygen, calculate the emprical formula:
P₂O₃
A compound contains 40g of carbon, 6.7g of hydrogen, and 53.5g of oxygen. Calculate the empirical formula of the substance:
CH₂O
An organic compound X, which contains carbon, hydrogen, and oxygen only, has an Mr of 86. When 0.43g of X are burnt in excess oxygen, 1.1g of carbon dioxide and 0.45g of water are formed. Calculate both the emprical and molecular formula of compound X
C₅H₁₀O
How may moles of carbon are there in 3 moles of carbon dioxide?
3 moles
How many moles of hydrogen are there in 2 moles of water?
4 moles
What is a crucible?
a ceramic container in whichsubstances may be melted or subjected to very high temperatures
What is a clay pipe triangle?
apparatus that is used to support a crucible being heated by a Bunsen burner
Why may the moles of water in a crystalline structure be calculated as lower than the true value when determining the formula of a hydrated salt?
If the salt is not heated for long enough, not all the water may have evaporated and be lost. Therefore not enough mass is lost and the moles of water is calculated as lower than the true value
Why may the moles of water in a crystalline structure be calculated as higher than the true value when determining the formula of a hydrated salt?
If the salt has been heated for too long, the salt may begin to decompose into other products. Some of these products may then be lost causing extra mass to be lost. Therefore the moles of water may be calculated as higher than the true value
FeSO₄xH₂O ( is a bullet point)
Mass of cruible (g): 19.39
Mass of crucible + hydrated salt (g): 21.90
Mass of crucible + anhydrous salt (g): 20.75
Calculate the Value of X
7
1210g
4.48g
What is relative molecular mass?
The mass of a molecule compared with the mass of 1/12th of a atom of carbon-12
What is relative formula mass?
The mass of a formula unit compared with 1/12th the mass of an atom of carbon-12
What is analysis?
Investigating the chemical composition of a substance
How is the water of crystallisation shown in a formula?
salt * xH₂O (* is a bullet point)
What is stoichiometry?
The molar relationship between the relative quantities of subtances taking place in a reaction (The mole ratio of the amount of each substance in a balanced chemical equation)
What is theoretical yield?
The maximum possible amount of product
Why may the theoretical yield not be reached?
- The reaction may not have gone to completion
- Other (side) reactions may have taken place alongside the main reaction
- Purification of the product may result in the loss of some product
What is the actual yield?
The amount of product obtained from a reaction
What is the equation for percentage yield?
percentage yield = (actual yield / theoretical yield) x 100
What is the limiting reagent?
The reactant that is not in excess and will be completely used up, causing the reaction to stop
What is the atom economy of a reaction?
A measure of how well atoms have been utilised in a reaction
What are the benefits of a high atom economy?
- It produces a large proportion of desired products and few unwanted waste products
- It is important for sustainability as it makes the best use of natural resources
What are the assumptions when calculating atom economy?
It is based solely on the balanced chemical equation for the reaction and assumes a 100% yield
What is the equation for atom economy?
atom economy = (Mr of desired products / Mr of all products) x 100
What does the sustainability of a chemical reaction depend on?
- Atom economy
- Sourcing reactants
- Products
- Percentage yield
What is the volume of 1 mole of any gas at room temperature and room pressure?
24dm³
What is the rule about the volumes of gases?
1 mole of any gas occupies the same volume at the same temperature and pressure
What is room temperature?
20°C / 293K
How do you convert from celcius to kelvin?
+273
What is 0K in celcius?
-273°C
What is room pressure?
1atm / 101kPa
What is the room temperature and pressure gas equation?
amount of moles = volume / 24
What is the ideal gas equation?
pV = nRT
(Pressure x Volume = Amount of gas x Ideal gas constant x Temperature)
What unit is pressure in, in the ideal gas equation?
Pascals
What unit is volume in, in the ideal gas equation?
Metres cubed (m^3)
What unit is amount of gas molecules in, in the ideal gas equation?
Moles (mol)
What unit is the ideal gas constant in, in the ideal gas equation?
J mol⁻¹ K⁻¹
What is the ideal gas constant?
8.314 J mol⁻¹ K⁻¹
What unit is temperature in, in the ideal gas equation?
Kelvin (K)
What is standard ambient temperature?
25°C / 298K
What is a completely elastic collision?
There is no loss of kinetic energy during the collision
What are the assumptions when using the ideal gas equation?
- There are no (or negligable) intermolecular forces between gas molecules
- The volume occupied by the molecules themselves is entirely negligible relative to the volume of the container
- The gas molecules are in constant random motion in straight lines
- The molecules behave as rigid spheres
- Pressure is due to collisions between the molecules and the walls of the container
- All collisions are prefectly elastic
- The temperature of the gas is directly proportional to the average kinetic energy of the molecules
What is molar gas volume?
The gas volume per mole
What is the units for molar gas volume?
dm^3 mol^-1
What are the steps for solving a molar calculation?
- Write out the balanced chemical equation
- Convert data given into moles
- Use the mole ratio to find required substance in moles
- Convert back into form required
What is the equation for % purity?
% purity = (Mass of pure chemical [g]) / (mass of impure sample [g]) x 100
What is the equation for an acid reacting with an alkali?
acid + alkali -> salt + water
What is the equation for an acid reacting with a base?
acid + base -> salt + water
What is the equation for an acid reacting with a carbonate?
acid + carbonate -> salt + water + carbon dioxide
What is an alkali?
A soluble base that gives an aqueous hydroxide
What is a base?
An insoluble oxide or hydroxide
A student dissolved 2.794g of an acid, HX, in water and made the solution up to 250.0cm3. The student titrated a 25.0cm3 of this solution against a 0.0614 mol dm-3 standard solution of Na2CO3(aq). 23.45cm3 of Na2CO3(aq) was required. Calculate the molar mass in g/mol of the HX given the equation for the reaction is:
Na2CO3(aq) + 2HX(aq) → 2NaX(aq) + CO2(g) + H2O(l)
97.0 g mol-1
How many decimal places should you do molar mass to?
1
A student dissolved 1.175g of an acid, H3X, in water and made the solution up to 250.0cm3. The student titrated a 20.0cm3 of this solution against a 0.10 mol dm-3 standard solution of NaOH(aq). 28.75cm3 of NaOH(aq) was required. Calculate the molar mass in g mol-1 of the H3X given the equation for the reaction is:
3NaOH(aq) + H3X(aq) → Na3X(aq) + 3H2O(l)
98.1 g mol-1
What is a milliletre in metric units?
cm^3
What is a litre in metric units?
1 dm^3
What is a standard solution?
A solution of a known concentration
1dm^3 of a solution with a sodium ion concentration of 0.1 mol dm^-3 is required. What volume of 0.2 mol dm^-3 sodium sulfate solution is needed to make this solution by dilution with water?
250 cm^3
How can a student heating a hydrated crystal ensure that all the water has been removed?
Heat until the mass is constant
