Acids and Alkali
Define an acid as a proton/H+ donor & a base as a proton/H+ acceptor
Proton/H+
H+ refers to an ion of hydrogen in which (just like regular hydrogen) there are no neutrons, but (unlike regular hydrogen) has no electron, which is why there’s a + after the H.
Acids:
An acid is defined as a chemical substance that can donate protons when dissolved in water. An acid can be defined under the following conditions
- pH – Less Than 7
- Turn Litmus Paper from Blue to Red
- Sour Taste
- Corrosive (when concentrated)
- Turns universal indicator from green to red
Base:
A base is defined as a chemical substance that can neutralize acids accept H+ ions and donat OH- ions (hydroxide). A base can be defined under the following conditions:
- pH – More Than 7
- Turn Litmus Paper to blue
- Soapy or Bitter Taste
- Corrosive (only to skin)
- Turns universal indicator from green to dark violet
Distinguish between aqueous solutions that are acidic, neutral or alkaline using the pH scale
pH stands for the power of Hydrogen and measures the concentration of an alkali or acid by measuring the concentration of Hydrogen Ions in an acidic, basic or neutral solution.
The H+ activity is logarithmic, meaning that each denomination is equal to the power of 10 with the sign reversed.
(e.g. Pure Water has a H+ concentration of 10-7 mol/dm3 so its pH is 7)
State the formula of common acids and bases:
Monoprotic:
Monoprotic Acids are acids that can release only one hydrogen ion per molecule during dissociation and they only have one equivalence point.
Diprotic:
Diprotic Acids are acids that can donate two hydrogen ions per molecule during dissociation.
Triprotic:
Triprotic Acids are acids that can donate three hydrogen ions per molecule during dissociation.
Describe strong and weak acids and bases in terms of the extent of ionization:
Strong Acid:
A strong acid that fully dissociates in water and releases a significant number of hydrogen ions.
Weak Acid:
A weak acid is one that only partially dissociates in water and releases a small number of hydrogen ions.
As with acids, bases can either be strong or weak, depending on their extent of ionization. When it comes to a strong base, it ionizes completely in an aqueous solution. Weak bases are those that don’t ionize completely in an aqueous solution.
Examples of Strong and Weak Acids and Bases:
Describe that strong acids and bases of equal concentrations have higher conductivities than weak acids and base:
Strong acids will be better at conducting electricity than weak acid at the same concentration and at the same temperature. A strong acid will have a lower pH than a weaker acid at the same concentration and at the same temperature. This is because strong acids are 100% dissociated producing more ions.
The conductivity of a diluted aqueous solution of the strong base will be greater than the conductivity of a diluted aqueous solution at the same concentration and temperature. This is because strong bases are 100% dissociated producing more ions.
Define neutralization reactions:
A neutralization reaction is when an acid and a base have a chemical reaction to form water and salt and involve the combination of H+ ions and OH- ions to generate water and keep the chemical reaction neutral.
Identify the acid and base needed to make different salts and write balanced equations to represent the reactions:
When making salts using acids and bases, it will also make water. The H(+) cation of the acid combines with the OH(-) anion of the base to form water (neutralizing it). The compound formed by the cation of the base and the anion of the acid is always a salt.
Example:
NaOH + HCl -> NaCl + H2O
The acid would be HCl while the base will be NaOH. Since the base has an OH(-) anion and the acid base a H(+), it will neutralize it. While the cation of the base and the anion of the acid is Na and Cl, it will make a NaCl, which is table salt.
Balanced Example:
Explain the use of neutralization in everyday life:
Stomachs contain hydrochloric acid, and too much of it can cause indigestion, Antacid tablets contain bases such as magnesium hydroxide to neutralise the extra acids. They use neutralization in multiple ways like to treat bee stings, acidity or gastric patients, cavities and tooth decay.
Identify products & reactants in chemical reactions:
In a chemical reaction, reactants are starting materials and are written on the left side of the equations. While products are the end results of the chemical reaction and are written on the right side of the equation.
Classify substances using the state symbols:
The state symbols in brackets show the physical state of the substances. There are 4 types of state symbols: Solid (s), liquid (l), gas (g) or dissolved in water (aq) which mean aqueous solution.
Identify reactions as ‘displacement” or “precipitate” means:
Displacement Reactions:
A reaction wherein the atoms is displaced by another term in a molecule:
An example would be Zinc + Copper Sulfate (Zn + CuSO4 -> Cu + ZnSO4)
As we can see that copper is the one that is displaced and the products are: Copper and Zinc Sulfate.
Displacement reactions occur when a metal is mixed with the ins of metal lower down in the electrochemical series. The atoms of the more reactive metals push their electrons on ions of the less reactive metal, displacing the less reactive metal.
Precipitate Reactions:
A chemical reaction occurring in an aqueous solution where two ionic bonds combine, resulting in the formation of an insoluble salt:
An example would be Lead Nitrate + Sodium Iodide or Pb(NO3)2 (aq) + 2NaI (aq) -> PbL2 (s) + 2NaNo3 (aq)
As we can see that the Lead Iodide has precipitated. Products are: Lead Iodide in a solid state and Sodium Nitrite in an aqueous solution.
A precipitation reaction occurs when two solutions containing different salts are mixed, and a cation/anion pair resulting in a combined solution forms an insoluble salt, this salt then precipitates out of the solution.
Balance chemical reactions for the reactions of acids with metals, metal oxides, metal hydroxides, hydrogen carbonate and carbonate.
When acids react with anything that is an alkali, metal, metal oxides, metal hydroxides and carbonate.
- Acid + Alkali -> Salt + Water
- Acid + Metal -> Salt + Hydrogen Gas
- Acid + Metal Hydroxide -> Salt + Water
- Acid + Metal Oxide -> Salt + Water
- Acid + Carbonate -> Salt + Carbon Dioxide + Water
