Acids
What is an Acid?
A substance which is less than 7 on the pH scale.
What is a Base?
Are all salts soluble in water?
No, not all salts are soluble in water. Eg: Calcium sulfate
Predict the value on the pH scale for Toothpaste.
8
Name three universal indicators.
1. Litmus Paper
2. Methyl orange
3. Phenolphthalein
4. Red cabbage
5. Thymolphthalein
Acid + Base --> ???
Acid + Base --> Salt + Water
Base + Metal --> ???
Base + Metal --> Salt + Hydrogen
What is a neutralisation reaction?
It is a reaction that occurs between an acid and base to produce water and a salt.
Predict the value of Milk on the pH scale.
6
Define the term 'universal indicators'.
A type of pH indicator that can be used to measure the concentration of hydrogenated ions in a substance.
Acid + Insoluble Base --> ???
(Insoluble bases are different than soluble bases)
Acid + Metal -->Salt + Water
What is the difference between alkali and a Base
Alkali are bases that are soluble in water. Bases are not readily soluble in water. All alakli are bases, but not all bases are alkali.
Give one example of an alkali and two examples of a base.
150: 2 Bases
150: 1 Alkali
What is the pH Scale?
If the pH scale is already effective in measuring the acidity or basicity of a substance, why use universal indicators?
Universal Indicators are more readily available as compared to pH scales. There is no need to control external environment when using a pH scale.
Ca + 2HNO3 --> ???
Ca + 2HNO3 --> Ca(NO3)2 + H2
2NaOH(aq) + H2SO4(aq) --> ???
2NaOH(aq) + H2SO4(aq) -->Na2SO4(aq) + 2H2O
Are all nitrates, sodium, and potassium salts soluble?
Yes
Why is it important to maintain a certain pH level in a swimming pool?
Chlorine, the disinfectant used in pools, effectively works at a certain pH level around 7.2-7.8. If it is not maintained, chlorine is much less effective at killing microorganisms and bacteria.
Identify the colour spectrum of the Universal Indicator in solution.
Red-Orange-Yellow-Green-Light Blue-Dark Blue-Violet
2HCl(aq) + Na₂CO₃(aq) --> ???
2HCl(aq) + Na₂CO₃(aq) --> 2NaCl(aq) + CO₂(g) + H₂O(l)
When alkali is dissolved in water, what type of ions does the water gain?
Hydrogenated ions are H+ ions. (Positive ions derived from Hydrogen)
Hydroxide ions are OH- ions. (Negative ions derived from Hydrogen bonded to Oxygen)
Alkali contains hydroxide ions, and when dissolved in water, the water gains excess hydroxide ions.
Explain 2 ways in which one can prepare a soluble salt involving the reaction of an acid.
1. Excess metal
2. Excess insoluble base
3. Excess insoluble carbonate
4. An alkali by titration
A solution is measured to have a pH of 10. Without adding any other chemicals, you adjust the pH of the solution to 7(neutral). Explain how you did so.
It is not possible to make the solution neutral. You have to add another chemical in order to bring its pH value to 7.
Briefly explain why someone might use a universal indicator instead of Litmus Paper for a series of unknown solutions. (2 reasons)
Litmus paper may only tell one if the substance is acidic or basic, but it will not show if it is a weak base, strong acid, or strong alkali. A universal indicator, however, has a more extensive colour spectrum and is more accurate in terms of measuring the intensity of the concentration of hydrogenated / hydroxide ions than Litmus Paper.