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Starter - Exam questions feedback. Learn precise definitions for masses, and acids and bases. For concentration calculations, make sure volumes are converted to dm 3 before completing calculations. Practice balancing equations, and predicting salts.

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## Starter - Exam questions feedback

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**Starter - Exam questions feedback**• Learn precise definitions for masses, and acids and bases. • For concentration calculations, make sure volumes are converted to dm3 before completing calculations. • Practice balancing equations, and predicting salts. • Learn how to calculate the relative atomic mass from percentage abundances.**Calculating the formula of hydrated salts**C grade – Be able to complete, and explain an accurate titration experiment B grade – Be able to use data to calculate the hydrated formula of a salt A grade – Conduct a titration experiment accurately, and use derived data to correctly calculate the formula of a hydrated salt.**The method**1) Record the mass of the hydrated salt. 2) Record the mass of the anhydrous salt. 3) Calculate the mass of water (subtract anhydrous from hydrated) 4) Using Mr of salt and water, calculate mole ratio of salt to water.**Example**Na2SO4.xH20**For assessment**What is your calculated formula? What did you do well? What do you need to improve on before completing and exam question on hydrated salts?**Calculating the formula of hydrated salts**C grade – Be able to complete, and explain an accurate titration experiment B grade – Be able to use data to calculate the hydrated formula of a salt A grade – Conduct a titration experiment accurately, and use derived data to correctly calculate the formula of a hydrated salt.**Plenary**What have you learned about AS Chemistry exam questions**Oxidation Number**C grade – Be able to explain reduction and oxidation in terms of electron transfer B grade – Be able apply the term oxidation number A grade –Be able to identify and calculate changes in oxidation number during a reaction**OIL RIG**Full equation: Mg + Cl2 MgCl2 Half equations: Mg Mg2+ + 2e- Cl2 + 2e- 2Cl-**Oxidising and reducing agents**Oxidising agents accept electrons Non metals: e.g. F2, Cl2, O2 Reducing agents donate electrons Metals: e.g. Na, Fe, Zn**Using oxidation numbers**Oxidation number is similar to the charge from GCSE. For example: Mg2+ has oxidation number = +2 O2- has oxidation number = -2 p43**All compounds must be zero overall**CO2 Charged ions must balance to the charge SO42-**Using oxidation numbers**Cr2O3(s) + 2Al(s) Al2O3(s) + 2Cr(s)**For assessment**Complete oxidation number questions on worksheet provided.**Oxidation Number**C grade – Be able to explain reduction and oxidation in terms of electron transfer B grade – Be able apply the term oxidation number A grade –Be able to identify and calculate changes in oxidation number during a reaction

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