3-Quantitative Chemistry Flashcards
What is relative formula mass?
Mr of a compound is the sum of the relative formula masses of the atoms in the numbers shown in the formula.
What is true about Mr in a balanced chemical equation?
Mr of products and reactants are equal in a balanced symbol equation.
what is the law of conservation of mass?
No atoms are lost or made during a chemical reaction, mass of products=mass of reactants
How do you calculate percentage mass of an element in a compound?
Ar X number of atoms of that element / Mr of the compound X 100
What is the mole?
How chemical amounts are measured
What is mass of 1 mol of a substance equal to?
Mass of 1 mol of a substance in grams = its relavtive formula mass
What is avagadro’s constant?
the number of atoms, molecules or ions, in a mol of any given substance
What is the value for avagadro’s constant?
6.02 X 10^23
How do you calculate number of moles?
number of moles = mass in g / Relative atomic mass (Mr)
Why may mass in a reaction appear to change?
A gas is involved and its mass has not been taken into account.
How can balancing numbers in a symbol equation be calculated from masses of reactants and products?
Converting masses in grams to amounts in moles and converting the numbers of moles to simple whole number ratios.
When do reactions stop?
When limiting reactant is used up
What is a limiting reactant?
The reactant that is completely used up - because it limits amount of products.
What is the volume of one mole of any gas at room temp and 1 atmospheric pressure?
24 dm^3
What can concentration of a solution be measured in?
Mass per given volume of solution, e.g g/dm^3
What is the calculation for concentration in mol/dm^3?
conc = no of moles/volume
*How do you convert mol/dm^3 to g/dm^3?
Mass = moles X Mr
Why is it not always possible to obtain a calculated amount of a product?
*reaction may not go to completion because its reversible
*some product may be lost when separated from reaction mixture
*some reactants may react differently than expected
What is the yield?
Amount of product obtained.
What is the formula for percentage yield?
percentage yield = mass of actual products/maximum theoretical mass X 100
Why can yield never be 100%
Some of the product or reactant always gets lost along the way.
What is atom economy?
Percentage of reactants forming useful products
Why is higher atom economy desired?
Less waste as more useful products, better economically?
What is the atom economy equation?
Mr of desired products/ Mr of all reactants
