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CHEMISTRY · Stage 9 · Chapter 12: Chemical Reactions 3 and Rates

Chemistry 12.8 Making salts from acids and carbonates

5 min read 6 parts Lesson 8 of 13

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Lesson summary

12.8 Making salts from acids and carbonates — Alhussan International Academy — Chemistry (Stages 7–9) notes: Describe how to make a salt from an acid and an insoluble carbonate, identify the gas produced and evaluate and improve the method.General equation — metal carbonate + aci…

  • Symbol equations
  • Positive result
  • Other gases
  • Fungicides
  • Reaction 1
  • Reaction 2

Part 1 of 6The reaction

  • General equation — metal carbonate + acid → salt + water + carbon dioxide.
    • calcium carbonate + hydrochloric acid → calcium chloride + water + carbon dioxide.
    • copper carbonate + sulfuric acid → copper sulfate + water + carbon dioxide.
  • Symbol equations — CaCO3(s) + 2HCl(aq) → CaCl2(aq) + H2O(l) + CO2(g) and CuCO3(s) + H2SO4(aq) → CuSO4(aq) + H2O(l) + CO2(g).
  • Fizzing — it shows carbon dioxide is released and how the reaction is progressing.

Part 2 of 6Test for carbon dioxide

  • Testbubble the gas through limewater (calcium hydroxide solution).
  • Positive resultthe limewater goes cloudy or milky because of tiny particles of insoluble calcium carbonate.
  • Other gasesdo not confuse it with hydrogen (squeaky pop) or oxygen (relights a glowing splint).

Part 3 of 6Choosing the method to make copper sulfate

  • Fungicidescopper sulfate is used by some farmers as a fungicide to destroy fungi that damage crops.
  • Reaction 1copper + sulfuric acid → copper sulfate + hydrogen, which needs concentrated acid and a high temperature.
  • Reaction 2copper oxide + sulfuric acid → copper sulfate + water, which can use dilute acid.
  • Reaction 3copper carbonate + sulfuric acid → copper sulfate + carbon dioxide + water, which can use dilute acid.
  • Industry and schoolindustry uses reactions 1 and 2, while school uses reaction 2 or 3 because reaction 1 is too hazardous.

Part 4 of 6Method to make a salt from a carbonate

  1. Measure 25 cm3 of dilute acid and pour it into a beaker, after doing a risk assessment.
  2. Add the carbonate powder one spatula at a time, stirring, so carbon dioxide forms and the mixture bubbles.
  3. Stop when some carbonate remains and there is no more bubbling, which shows all the acid has reacted.
  4. Filter the mixture so the unreacted carbonate stays in the filter paper and the salt solution is collected.
  5. Heat the solution in an evaporating basin until blue crystals start to form around the edge.
  6. Let it cool in a warm, dry place so the water evaporates slowly and crystals form, then filter, wash and dry them.
  • Stagesreaction, filtration, evaporation and crystallisation.
  • Evaporating basincollecting the filtrate straight into it means the solution does not need pouring from one container to another.
  • Safety of carbonatesthey are safer than reactive metals, and add small portions so the mixture does not froth over.
  • Soluble carbonateswith sodium carbonate an indicator or titration is needed to find the neutral point.

Part 5 of 6Evaluating and improving the method

1Problem
— Dan made a smaller mass of crystals than expected because some solution spat out during evaporation.
2Improvement1 point
— heating over a water bath rather than a flame heats the solution more evenly and prevents spitting.
  • The second attempt gave a greater mass of crystals.
3Rates experiment1 point
— the volume of gas produced in a fixed time, or the time for fizzing to stop, can compare powdered and lump carbonate.
  • 5.0 g of calcium carbonate reacting with excess acid loses 2.2 g in mass, which is the mass of carbon dioxide released.

Part 6 of 6Everyday links

  • Limestone and marblebuildings and statues are carbonates, and acid rain makes the stone fizz slowly and wear away.
  • Indigestion tabletsthey contain carbonates that neutralise excess stomach acid.
  • Soilcalcium carbonate is added to soil to reduce acidity.
  • Identifying carbonatesadd dilute acid to an unknown solid and test any gas with limewater.
Reaction typeProducts
Acid + metalSalt + hydrogen
Acid + oxideSalt + water
Acid + carbonateSalt + water + carbon dioxide

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