Topic 5a: Calculations Flashcards
What is an empirical formula?
All substances have these. This is the simplest whole number ratio of atoms or ions of each element in a substance.
What is the molecular formula?
Substances that are made from simple molecules also have a molecular formula. This represents the actual number of atoms of each element in one molecule.
Define what is meant by the ‘formula’ of a compound?
The formula of a compound is its molecular formula if it’s a simple molecule or its empirical formula is its a giant lattice structure.
What is meant by the relative formula masses of a substance?
Then is the sum of the relative atomic masses of all the atoms or ions in its formula. Relative atomic masses are given in the periodic table above the element.
Relative formula mass = Mr
Relative atomic mass = Ar
How can the empirical formula be calculated?
The empirical formula of a compounds can be calculated from the masses if the elements used to make it and the RFM of the the element.
- Mass (g)
- Relative atomic mass of elements
- Divide the mass of elements by its RFM
- Divide both numbers by smallest number of previous answer
- Put it in a ration to each other
What is the law of conservation of mass?
When a solute is dissolved in a solvent to make a solution, the mass of the solution is equal to the mass of the solute and solvent. The overall mass of the substance does not change.
What is meant by concentration?
The amount of solute dissolved in a stated volume of its solution.
What is the equation for calculating concentration in g dm3?
Concentration = mass of solute (g)/volume of solution (dm3)
What is 1dm3 equivalent to?
1dm3 = 1000cm3 = 1 litre
What is a non-enclosed system?
Another term for an open system.
A system into or from which substance can enter or leave, such as a reaction inside an open test tube.
What is a precipitate?
An insoluble substance that is formed when 2 soluble substances react together in solution.
What is an closed system?
When substances cannot enter or leave and observed environment. E.g a stoppered test tube.
When some solid are heated what do they appear to do?
Som solids appear to gain in mass when they are heated in a non-enclosed system. However, in all systems that mass of the products is always the same as the mass of the reactants.
How many particles does 1 mole consist of?
6.02x10 to the power of 23. This is known as the Avogadro constant. These particles can be atoms, molecules or ions.
What is the Avogadro constant?
6.02x10 to the power of 23
