3. Quantitative Chemistry Flashcards
Describe the Law of Conservation of mass
The law of conservation of mass states that no atoms are lost or made during a chemical reaction, so the mass of the products equals the mass of the reactants.
Why do we balance out chemical reactions?
Chemical reactions are balanced out because of the law of conservation of energy which states that atoms are not made or lost during a chemical reaction, so the number of atoms of the products and reactants must be the same
The total mass of reactants is equal to…
The total mass of reactants is equal to the total mass of products
What is the relative formula mass?
The relative formula mass (Mr) is the sum of the relative atomic masses of the atoms shown in the formula/compound
The total Mr of all the reactant particles is equal to…
The total Mr of all the reactant particles is equal to the total Mr of all the product particles
How do we calculate the percentage by mass in a compound?
Why do some reactions appear to involve a change in mass?
Some reactions may appear to involve a change in mass because a reactant or product is a gas and its mass has not been taken into account
- For example, oxygen entering an open system and reacting with metals, or gas escaping an open system
- Another example is thermal decomposition, where a metal carbonate breaks down to form metal oxide and carbon dioxide - which escapes into the air
What is a closed system?
A closed system is where substances cannot enter or leave
What is the issue with taking measurements?
Whenever a measurement is made there is always some uncertainty about the result obtained
What is resolution?
Resolution is the smallest change that can be seen or shown
e.g. 1mm in a ruler, 0.1g on a digital balance reading to 1dp
How do we measure uncertainities of a single reading?
Uncertainities are given as ± a value
- To calculate the uncertainites when reading a single measurements, we divide the resolution by two and then ± to the reading
How do we calculate the range and uncertainity of values in repeat measurements?
In science, the range of a set of values is the difference between the maximum and the minimum value
The uncertainity of a set of values is the range / 2
What is the symbol for the unit moles?
Mol
What are moles?
Mole is the amount of a substance, where amount refers to the number of atoms it contains
Describe the number of atoms, molecules or ions in 1 mole of a substance
- 1 mole of any substance contains the same number of atoms, molecules or ions as one mole of any other substance
- 1 mole of a substance contains 6.02 x 10<sup23</sup> particles
What is the mass of one mole of a substance equal to? (e.g. sodium)
The mass of one mole of a substance is numerically equal to its relative formula mass in grams
e.g. the Mr of sodium is 23, so one mole of sodium weighs 23g
What is the avogadro constant?
The avogadro’s constant is the number of atoms, molecules or ions in one mole of a substance, which is 6.02 x 1023
Carbon has a relative atomic mass of 12
How many particles are in one mole of carbon?
How much does 1 mole of carbon weight?
- One mole of carbon has 6.02 x 1023 carbon atoms
- One mole of carbon atoms is 12g
FACT, NO ANSWER
In one mole of carbon (C), the number of atoms is the same as the number of molecules in one mole of carbon dioxide (CO2)
(6.02 x 1023)
What is the formula that links moles, relative formula mass and mass together?
Moles = mass / mr
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What is a limiting reactant?
A limiting reactant is the reactant that is completely used up and limits the amount of products
Why is it common to use in excess of one of the reactant in a chemical reaction?
To ensure that all of the other reactant is used
How do we find out the limiting reactant?
By calculating the expected and actual moles
