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# gcse science C4 - B

### specific for ocr gateway additonal science B.

Question | Answer |
---|---|

how do you work out the relative formula mass? | 1. work out the inside of the bracket first. 2. now multiply the bracket by any numbers below it. 3. work out the outside of the bracket 4. finally, add them all together |

what is an example of how to work out the relative formula mass? | Al(OH)3 Al = 27 O = 16 H = 1 1. 16 + 1 = 17 2. 17 x 3 = 51 3. = 27 4. 26 + 51 = 78 |

what does percentage yield mean? | the amount of product which is produced in a reaction |

what is the equation to work out percentage yield? | percentage yield = actual yield / predicted yield x 100 |

what is actual yield? | the amount of product made |

what is predicted yield? | the amount of product that should have been made |

what are the 3 steps to use when figuring out percentage yield? | 1. find the relative formula mass of the reactant 2. find the relative formula mass of what you are trying to find 3. work out the amount of product made using ratios |

example of how to work out percentage yield? | ZnCO3 - ZnO + CO2 Q. find out how much C02 is made when 625g of ZNCO3 decomposes. A. 1. 65 + 12 + 16 + 16 + 16 = 125 2. 12 + 16 + 16 = 44 3. so if 125g of ZnCO3 gives 44g of C02, then 625g of ZnCO3 gives 625/125 x 44, = 220g of CO2 |