balance1.gifmulti-word fill quiz 9Hwf4 on "Using chemistry"
(a doc brown worksheet for QCA KS3 science-chemistry)

Site Meter* Do online OR printout, do, return to check answers. * KS3 Science Index * EMAIL comment?query * Doc Brown's Chemistry updated June 11th 2009 *

   20      32      48      6      60      8      atoms      conservation      equal      gains      gas      lose      loses      mass      oxide      predictions      products      reactants      weigh   
1. In a chemical reaction combine in different ways to form new .

balance2.gif2. Whatever the change, you cannot any atoms. This is known as the law of of . It means that if you could weigh the at the start, and then compare this with the of all the formed at the end, they would be .

3. Two sorts of situation can appear at first sight to contradict this law.
3a. When a metal is heated in air it mass in forming the metal oxide.
3b. When a carbonate dissolves in acid, the mixture mass.
3c. Both these situations involve the 'adding' or losing' of a , which is rather difficult to !

balance3.gif4. From the 'law' in 2. you can make about the quantities of chemicals involved in a reaction.
4a. For example, 24g of magnesium burns in air and combines with 16g of oxygen to form 40g of magnesium , even if you can't weigh the oxygen!
4b. This means 36g of magnesium will combine with 24g of oxygen from the air to form g of magnesium oxide.
4c. If g of magnesium is burned it combines with 4g of oxygen to form 10g of magnesium oxide.
4d. Burning 12g of magnesium will combine with g of oxygen to make g of magnesium oxide
4e. burning g of magnesium will combine with g of oxygen to make 80g of magnesium oxide.