Quantiatative chemistry Flashcards
What is 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.
What is the relative formula mass (Mr) of a compound and how is this useful in chemical equations?
The relative formula mass (Mr) of a compound is the sum of the relative atomic masses of the atoms in the numbers shown in the formula.
In a balanced chemical equation, the sum of the relative formula masses of the reactants in the quantities shown equals the sum of the relative formula masses of the products in the quantities shown.
Why do some equations appear to have a change in mass from the products to reactants even though all mass must be preserved?
Some reactions may appear to involve a change in mass but this can usually be explained because a reactant or product is a gas and its mass has not been taken into account.
Chemical amounts are measured in moles, what is a mole of a substance?
The symbol for the unit mole is mol.
The mass of one mole of a substance in grams is numerically equal to its relative formula mass.
The number of atoms, molecules or ions in a mole of a given substance is the Avogadro constant. The value of the Avogadro constant is 6.02 x 10(power 23) per mole.
How can the masses of reactants and products be calculated in an equation using moles?
Chemical equations can be interpreted in terms of moles. For example:
Mg + 2HCI —> MgCI₂ + H₂
shows that one mole of magnesium reacts with two moles of hydrochloric acid to produce one mole of magnesium chloride and one mole of hydrogen gas.
Using the equation: Mass (in grams) = Mr x Moles
To find the mass of the hydrochloric acid,
36.5 (Mr) x 2 (Moles) = 73 grams (Mass)
How can symbol equations be balanced using the masses of the products and reactants?
The balancing numbers in a symbol equation can be calculated from the masses of reactants and products by converting the masses in grams to amounts in moles and converting the numbers of moles to simple whole number ratios.
What is the limiting reactant in a chemical reaction?
In a chemical reaction involving two reactants, it is common to use an excess of one of the reactants to ensure that all of the other reactant is used. The reactant that is completely used up is called the limiting reactant because it limits the amount of products.
What is the equation for calculating the concentration of a solution.
Mass (in grams) = concentration (in g/dm³) x volume (dm³)
