P1 - Quantitative Chemistry Flashcards
How would you find the relative formula mass (Mr) of a compound.
Add together the relative atomic mass (Ar) of all the atoms in the molecular formula.
How could you work out the percentage mass of an element in a compound ?
Percentage mass of an element in a compound = ((Ar × number of atoms of that element) ÷ Mr of the compound) × 100
What is a mole ?
The name given to an amount of a substance ?
What does one mole of a substance mean ?
An amount of that substance that contains 6.02 × 10^23 particles.
What is the formula for the number of moles in a given mass ?
Number of moles = mass in g (of element/compound) ÷ Mr (of element/compound)
What happens to the total mass during a chemical reaction ?
No atoms are destroyed or created, meaning same number and types of atoms are on each side of the reaction equation, and no mass is lost or gained - meaning mass is conserved during a reaction.
What does it mean if the mass in a reaction seems to increase ?
One of the reactants is a gas that’s found in air and all products are not gases. Before reaction gas is floating in the air and unable to be measured, after reaction gas becomes contained in reaction vessel - so total mass inside increases.
What does it mean if the mass in a reaction seems to decrease ?
One of the products is a gas and all reactants are not gases. Before reaction all reactants contained in reaction vessel, but after reaction gas can escape an unenclosed vessel as it’s formed and is unable to be measured - so total mass inside decreases.
What is an avogadro constant number of particles ?
6.02 × 10^23 particles.
What do the big numbers in front of the chemical formulas for reactants or products tell you ?
How many moles of each substance takes part or is formed during the reaction.
What do the little numbers after the elements tell you ?
The number of atoms of each element there are in each of the substances.
How can you balance a symbol equation using reacting masses ?
Divide the mass of each substance by its relative formula mass to find the moles, divide the number of moles of each substance by the smallest number of moles in the reaction, if any of these aren’t whole numbers multiply all by the same amount so they all are, write the balanced symbol equation by putting these numbers in front of the chemical formulas.
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