Calculations
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What is the first step in writing and balancing equations?
Write the correct formulas for the reactants and products.
What should be added to each product and reactant if needed?
Add in state symbols (s) (l) (g) (aq).
How do you balance an equation?
Count the number of atoms of each element on both sides and balance them by writing a big number in front of the formula.
What is the relative atomic mass (Ar)?
The weighted average mass of the isotopes of the element compared to Carbon 12.
What is the relative formula mass (Mr)?
To find Mr, take the atomic masses and add them up.
How do you calculate the Mr of a compound?
Add the atomic masses of all elements in the formula.
What is a hydrated compound?
A compound that has water loosely attached to it, known as water of crystallisation.
How do you find the % composition of an element in a compound?
Divide the total mass of the element in the compound by the relative formula mass and multiply by 100.
What does one mole of a substance contain?
One mole contains 6 x 10^23 particles (atoms, molecules, ions).
How do you convert mass to moles?
Use the formula: Number of Moles = Mass (g) / RFM.
What is the empirical formula?
The simplest ratio of atoms in a compound.
How do you find the empirical formula?
• Find the moles of each element. 2. Divide by the smallest number. 3. Multiply to get whole numbers if needed.
How do you find the molecular formula from the empirical formula?
Use the formula: n x empirical formula = Mr, where n is the ratio.
What is the process to find the formula of magnesium oxide by combustion?
• Find mass of magnesium before heating. 2. Find mass of magnesium oxide after heating. 3. Calculate the mass of oxygen by finding the difference.