SC8 - Acids ✓

Question 1

SC8a - All solutions are one of what three things?

Answer 1

• Acidic
• Neutral
• Alkaline

Question 2

SC8a - What determines if a solution is acidic or alkali?

Answer 2

• 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

Question 3

SC8b - Describe how a solution can be concentrated or dilute

Answer 3

• 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)

Question 4

SC8b - Describe how a solution can be strong or weak

Answer 4

• 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

Question 5

SC8c - What is a base?

Answer 5

• A base is a substance that neutralises an acid.
• Base(s) + acid(aq) → salt(aq) + water(l)

Question 6

SC8c - Describe how neutralisation occurs in terms of ions.

Answer 6

• 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

Question 7

SC8c CP - Describe how to prepare copper sulfate from copper oxide and sulfuric acid.

Answer 7

• 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

Question 8

SC8d - What is a soluble base?

Answer 8

An alkali

Question 9

SC8d CP - Investigate how the pH of an hydrochloric acid changes based on the amount of calcium hydroxide in it

Answer 9

• 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

Question 10

SC8f - Acid + Metal →

Answer 10

Acid + Metal →Salt + Hydrogen

Question 11

SC8f - Acid + Carbonate →

Answer 11

Acid + Carbonate → Salt + Water + Carbon Dioxide

Question 12

SC8f - How do you work out the ionic equation of a metal + acid reaction?

Answer 12

• [Mg can be replaced with any metal but may be balance differentyl]
• Mg(s) + 2H⁺(aq)→ Mg^2-(aq) + H₂(g)
• The other ions (sulfate, chloride etc.) are spectator ions as they don’t change form either side of the equation

Question 13

SC8f - Using the ionic equation

Mg(s) + 2H⁺(aq) → Mg^2-(aq) + H₂(g)

How do you work out the half equations?

Answer 13

Mg(s) → Mg^2-(aq) + 2e^-

2H⁺ (aq) + 2e^- → H₂(g)

Question 14

SC8e - What method can be used to work out how much acid to use to obtain pure dry crystals of salt?

Answer 14

Repeated titration (method in SC14) followed by crystallisation using the results.

Question 15

SC8g - What is a precipitate reaction?

Answer 15

When two soluble substances in solutions react and form an insolube precipitate as one of its products

Question 16

SC8g - What are the rules for solubility?

Answer 16

• 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

Question 17

SC8g - What happens when two solutions containing soluble salts are reacted?

Answer 17

• The ions from the salt switch.
• e.g copper sulfate + potassium carbonate → copper carbonate + potassium sulfate

Question 18

SC8g - How do you form an insoluble salt from silver nitrate and sodium chloride?

Answer 18

• Pour some silver nitrate solution into some sodium chloride solution in a beaker
• This will react forming a precipitate of silver chloride
• Use a filter funnel with filter paper to filter this out
• Wash the precipitate with distilled water
• Remove the filter paper containing the salt and place in a warm oven to dry