In the extraction of aluminium from bauxite ore, several steps are involved. In one of these, sodium hydroxide (NaOH) and water react with aluminium oxide (Al2O3) to produce sodium tetrahydroxoaluminate (NaAl(OH)4). Write a balanced chemical equation for this reaction. Explain how you can test that your equation is balanced. The plant producing the baking trays generates about 6.5 tonnes of mixed combustible waste (from raw material coming in) per year. This goes to a waste-to-energy power station, which has an overall efficiency of 24%. If the heat of combustion of the waste is 7.6 MJ kg*1, calculate the amount of useful electrical energy generated each year by burning the waste. Explain your working and give your answer in units of MJ to 2 significant figures.