Unit 7 - Acids, bases and salts Flashcards
Properties of acids
- Contain H^+ ions
- Soluble in water
- Sour to the taste
- Corrosive
Properties of bases
- Found as metal oxides (O^2-), metal carbonates (CO3^2-), metal hydroxides (OH^-) or ammonia
- Some are soluble in water - called alkalis and are metal hydroxides
- Soapy to the touch
- Corrosive
Indicator
A chemical substance that changes color with changing H^+ concentration
Types of indicators
- Litmus
- Methyl orange
- Universal indicator paper
- Thymolphthalein
Litmus colors for acids and bases
- Acid = Red
- Base = Blue
Methyl orange colors for acids and bases
- Acid = Red
- Base = Yellow
Universal indicator paper colors for acids and bases
- Strong acid = Red
- Weak acid = Orange/Yellow
- Strong base = Purple
- Weak base = Blue
Thymolphthalein colors for acids and bases
- Acid = colorless
- Base = Blue
pH scale values
- 0-6 = Acid
- 7 = Neutral
- 8-14 = Alkaline (base)
Equation for an acid and metal reacting together
Acid + Metal –> Salt + Hydrogen
Equation for an acid and base reacting together
Acid + Base –> Salt + Water
Equation for an acid and metal carbonate reacting together
Acid + Metal carbonate –> Salt + Carbon dioxide + Water
Equation for an acid and ammonia reacting together
Acid + Ammonia –> Salt
Products of ammonium salts reacting with metal hydroxides
- Ammonia
- Salt
- Water
Brønsted-Lowry theory of acids and bases
- Acid is capable of donating a proton
- Base accepts a proton
- Water is amphoteric - can act as both acid and base
- Strong acids and bases ionize completely in water
- Weak acids and bases only partially ionize in water
- The conjugate base of an acid is formed after the acid donates the proton
- The conjugate acid of a base is formed after the base accepts a proton
- The two species in a conjugate acid-base pair have the same molecular formula except the acid has an extra proton compared to the conjugate base
Elements that make acidic oxides
Non-metals
Elements that make basic oxides
Metals
Amphoteric
A substance that behaves both as an acid or a base
Examples of amphoteric oxides
- Aluminum oxide
- Zinc oxide
Possible reactants that amphoteric oxides can react with
- Acid and bases to form a salt and water
Salts
Ionic compounds made of positive ions/cations and negative ions/anions
Sources of cations
- Metal
- Metal oxide
- Metal hydroxide
- Metal carbonate
Sources of anions
- Hydrochloric acid (Cl^-)
- Sulfuric acid (SO4^2-)
- Nitric acid (NO3^-)
Salt in a solid state
Crystals
Hydrated salt
When water molecules get inside the crystal structure and chemically bond to the metal ion - known as water of crystallization
Anhydrous salt
When crystals exist with no water molecules bonded into the crystal structure
Representation for water of crystallization
Dot between the salt and water to show they have been reacted together
Method for getting a salt from an acid and base reaction
- Place a known volume of acid using a volumetric pipette into a conical flask
- Add a few drops of the indicator
- Add the alkali to the acid until the indicator changes color
- Record the volume of alkali added to the acid
- Repeat without the indicator or add decolonizing charcoal (will have to be heated and filtered)
- Transfer to an evaporating dish and heat to evaporate off some of the water until crystals form
- Leave to cool
- Filter to get the crystals
- Dry the crystals on filter paper
Soluble salts
- All ammonium, sodium and potassium salts
- All nitrate salts
- Nearly all chloride, bromide and iodine salts
- Nearly all sulfates
- Ammonium, sodium and potassium carbonates salts
- Ammonium, sodium and potassium hydroxide salts
Insoluble salts
- Silver chloride, solver bromide, solver iodide and lead chloride
- Barium sulfate, calcium sulfate and lead sulfate
- Most carbonates
- Most hydroxides
Products when two solutions containing soluble salts mix
- One salt forms an insoluble solid/precipitate and the solution becomes cloudy
- The other product is a soluble salt that stays in the solution
Method of preparing an insoluble salt
1.Mix equal quantities of the two soluble salts
2. Filter to remove the insoluble salt or precipitate
3. Wash the precipitate with water
4. Leave to dry
