1e) Chemical Formulae and Chemical Equations

Word equations and Balanced chemical equations are used to represent the reactions studied in this specification. In a chemical equation you have to use state symbols: (s), (l), (g) and (aq) in chemical equations to represent solids, liquids, gases and aqueous solutions

Water of Crystallisation:

• solid salt with water is HYDRATED
• salt without water is ANHYDROUS
• calculate it by:

1. Working out the mass
2. Number of moles of water lost
3. ratio of anhydrous salt made
4. ratio of anhydrous to mole of Water
5. X must be a whole number

Empirical formula:

Is the simplest formula that tells you the ratio of different elements in the compound

1. List all the elements in the compound
2. Write underneath the experimental masses/ percentage
3. Divide by A_r of elements
4. Change to simple ratio by multiplying and/or dividing them by well chosen numbers
5. Simplify ratio

Molecular Formula:

A compound tells you the actual number of atoms each element in a single molecule

Calculate Masses in Reactions:

1. Write out the balanced equation
2. Work out the and multiply them by balancing numbers in the equation
3. Apply the rule: Divide to get one, then multiply to get all

Percentage Yield:

= (mass obtained/ mass predicted) x 100

Moles and Concentration

Concentration = Number of Moles / Volume