SC8a - All solutions are one of what three things?
SC8a - What determines if a solution is acidic or alkali?
- The concentration of hydroxide ions and hydrogen ions when dissolved in water.
- An even balance of both will lead to all of them forming water and an excess of neither.
- An excess of hydrogen ions makes a solution and an excess of hydroxide ions makes a solution alkaline.
- The concentration of theses ions determiens the pH of a solution
SC8b - Describe how a solution can be concentrated or dilute
- A concentrated solution contains a high concentration of excess ions (more per unit volumes)
- A dilute solution contains a low concentration of excess ions (less per unit volumes)
SC8b - Describe how a solution can be strong or weak
- When a strong acid/alkali is dissloved in water, their molecules fully dissociate (break up) producing a high concentration of ions
- When a weak acid/alkali is dissolved in water, their molecules don't fully dissociate and so they produce a low concentration of ions
SC8c - What is a base?
- A base is a substance that neutralises an acid.
- Base(s) + acid(aq) → salt(aq) + water(l)
SC8c - Describe how neutralisation occurs in terms of ions.
- The base releases hydroxide ions when dissolved in the acid
- These bond with the excess hydrogen ions to form water
- The other elements in the base and the acid bond to form a salt
SC8c CP - Describe how to prepare copper sulfate from copper oxide and sulfuric acid.
- Mix copper oxide into a beaker of hydrochloric acid till it is in excess
- Gently warm the mixture to speed up the reaction
- Filter to remove the excess copper oxide
- Heat up the solution in an evapourating basin over water on a bunsen burner
- Right before all the liquid has evapourated, remove it from the heat and leave it to evapourate naturally
- The longer it takes, the larger the crystals of copper sulfate formed
SC8d - What is a soluble base?
SC8d CP - Investigate how the pH of an hydrochloric acid changes based on the amount of calcium hydroxide in it
- Usign a measuring cylinder, add 50cm³ of hydrochloric acid to a beaker
- Keep pieces of universal indicator paper on white tiles
- Dip the end of the glass rod into the acid and dab it onto the paper
- Estimate the pH of it and dab the rod dry
- Add 0.3g of calcium hydroxide powder to the acid and then repeat this
- Keep adding 0.3g at a time recording the the pH each time until you've added 2.4g
- Draw out a graph for the values of pH and calcium carbonate added
SC8f - Acid + Metal →
Acid + Metal →Salt + Hydrogen
SC8f - Acid + Carbonate →
Acid + Carbonate → Salt + Water + Carbon Dioxide
SC8f - How do you work out the ionic equation of a metal + acid reaction?
- [Mg can be replaced with any metal but may be balance differentyl]
- Mg(s) + 2H+(aq)→ Mg2-(aq) + H2(g)
- The other ions (sulfate, chloride etc.) are spectator ions as they don't change form either side of the equation
SC8f - Using the ionic equation
Mg(s) + 2H+(aq) → Mg2-(aq) + H2(g)
How do you work out the half equations?
Mg(s) → Mg2-(aq) + 2e-
2H+ (aq) + 2e- → H2(g)
SC8e - What method can be used to work out how much acid to use to obtain pure dry crystals of salt?
Repeated titration (method in SC14) followed by crystallisation using the results.
SC8g - What is a precipitate reaction?
When two soluble substances in solutions react and form an insolube precipitate as one of its products
SC8g - What are the rules for solubility?
- All PANS are soluble (potassium, ammonium, nitrates and sodium)
- Chlorides apart from silver and lead are soluble
- Sulfates apart from lead, barium and calcium are soluble
- The only carbonates and hydroxides that are soluble are the PANS
SC8g - What happens when two solutions containing soluble salts are reacted?
- The ions from the salt switch.
- e.g copper sulfate + potassium carbonate → copper carbonate + potassium sulfate
SC8g - How do you form an insoluble salt from silver nitrate and sodium chloride?