5.1.17

Changing Mass

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Changing Mass

In chemical reactions, substances may seem to lose or gain mass. Normally, one of the reactants (or products) is a gas. Gas can escape into the surrounding environment.

Illustrative background for Burning of woodIllustrative background for Burning of wood ?? "content

Burning of wood

  • When wood is burnt, it releases carbon dioxide and water (and often other gases).
  • These gases can escape into the atmosphere. These gases can't be weighed easily at the end of a reaction.
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Corrosion of metals

  • The mass of the oxide produced will be larger than the mass of the starting metals because oxygen atoms from the atmosphere have been added:
    • E.g. 2Mg + O2 → 2MgO
  • The change in mass will equal the mass of the oxygen atoms which have been added.
Illustrative background for Zinc + hydrochloric acidIllustrative background for Zinc + hydrochloric acid ?? "content

Zinc + hydrochloric acid

  • During this reaction, you would expect the mass of the flask and reactants (zinc and hydrochloric acid) to decrease.
  • This is because the hydrogen gas produced will escape from the flask.
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Calculating mass

  • 2Na + Cl2 → 2NaCl.
  • If 2.30g of sodium reacted in excess chlorine and 5.85g of NaCl was produced, we can calculate the mass of chlorine reacted.
  • 5.85g - 2.30g = 3.55g of chlorine reacted.

Jump to other topics

1States of Matter

2Elements, Compounds & Mixtures

3Atomic Structure

4The Periodic Table

5Chemical Formulae, Equations & Calculations

6Bonding

7Electrolysis

8Groups of the Periodic Table

9The Atmosphere

10Reactivity Series

11Metal Extraction

12Acids & Alkalis

13Chemical Tests

14Physical Chemistry

15Organic Chemistry

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