10th March Revision Flashcards
What is the conservation of Mass?
the conservation of mass is when the mass of the products in a chemical reaction must equal the mass of the reactants.
What is Relative Atomic Mass?
it is the ratio of the average mass of atoms of an element in a given sample to one unified atomic mass unit
What is Relative Formula Mass?
The relative formula mass of a substance is the weighted average of the masses of the formula units relative to 1/12 of the mass of a carbon-12 atom.
How can I find the mass of a reactant or product from a
balanced symbol equation?
1) Write the balanced chemical equation for the reaction.
2) Work out the formula masses for the relevant substances and the number of molecules of each.
3) Work out the ratio of reactant to product (or product to reactant) for the required situation. (You want the unknown on the top!)
4) Work out the ratio of reactant to product (or product to reactant) from the masses given.
5) Write them equal to each other.
6) Rearrange the equation and work out the answer.
Why does the mass of reactants appear to increase or
decrease in some chemical equations?
the mass in a reaction is constant if it is a closed system. mass changes only occur because a gas is being released into the atmosphere, or because a gas from the atmosphere is being used as a reactant - no atoms are being created or destroyed, just rearranged. CONSERVATION OF MASS
How many atoms or molecules are in one mole of
substance?
You’d go about calculating this by using Avogadro’s number. 6 X 10 to the power of 23
How can I calculate the mass of one mole of a
substance?
1) Calculate the molar mass of the substance
2) Divide it by Avogadro’s Number
What is the Avogadro constant?
6 x 10 to the power of 23
How do I calculate the number of moles in a given
mass of that substance?
moles = mass ÷ molar mass
Example:
Q) 10 mol of carbon dioxide has a mass of 440 g. What is the molar mass of carbon dioxide?
a) molar mass = mass ÷ number of moles = 440 ÷ 10 = 44 g/mol
How can I calculate the theoretical mass of a
substance in a balanced symbol equation?
percentage yield = actual yield
—————– x 100
theoretical yield
What are limiting reactants?
The limiting reactant is the substance that is totally consumed when the chemical reaction is complete. The amount of product formed is limited by this reagent, since the reaction cannot continue without it.
What is the unit for concentration in a solution?
dm cubed
Why are some products lost during an experiment,
even though no atoms can be lost or gained?
Mass is never lost or gained in chemical reactions. We say that mass is always conserved. In other words, the total mass of products at the end of the reaction is equal to the total mass of the reactants at the beginning.
How do you work out atom economy?
mass of atoms in desired product
———————————————— x 100%
mass of atoms in reacatants
How do you work out Moles?
moles = CONCENTRATION x VOLUME (dm cubed)
