Properties of Acids and Bases And the pH scale

Properties of Acids The acids we eat can be described as: Sour-tasting Examples of Common Acids Acid (Common Name) Source or Use - Vinegar (10% Acetic Acid)Salad Dressing - Citric AcidFresh Fruit - Ascorbic AcidVitamin C - Carbonic AcidCarbonated Soft Drinks - Lactic AcidSour Cream - Acetylsalicylic AcidAspirin Some acids react with metals and glass, these are described as corrosive. If released into the environment, these acids can cause serious damage.

Properties of Bases The bases we eat can be described as: bitter-tasting slippery when rubbed between the fingers Examples of Common Bases Base (Common Name)Source or Use - Sodium BicarbonateBaking Soda - Potassium SulphiteFood Preservatives - Aluminum HydroxideAntacid Bases are good conductors of electricity because they release hydroxide ions (OH-) when dissolved in water. Some bases are just as dangerous as acids and can burn skin. (Example: Sodium Hydroxide…Drain Cleaner & Ammonium Hydroxide…Window Cleaner)

The pH Scale Acids and bases are pure substances and compounds. Some are called “weak” and some are called “strong.” Strong acids and bases are extremely reactive and corrosive. The strength of an acid is determined by its ability to produce hydrogen ions when mixed with water. Example; HCl – Hydrochloric Acid HF – Hydroflouric Acid H 2 SO 4 – Sulfuric Acid The number of hydrogen ions produced when an acid is mixed with water determines the acid properties of the solution. The greater the number of hydrogen ions, the lower the pH value.

The pH value is usually expressed on a scale from 0 to 14. pH Values of less than 7 are acidic, greater than 7 are basic or alkaline. The number 7 is neutral (Pure water).

Contributors of strength The strength of an acid or base is dependant on two factors The percent ionization Percentage of H+ ions released by the molecule Concentration

HCl a strong acid

Strong acids and bases Percent ionization is the number of molecules out of 100 that will separate into the parts of an acid or base once placed in water For example HCl will completely break apart in to H + and Cl in water, this makes it a strong acid This is dependant on how strong the bonds are between the atoms Similarly with Bases, strong bases will release a high percentage of the OH - ions from the chemical bond Concentration involves the number of H + or OH - ions in a given unit of volume Strong acid has low pH, high percent ionization, weak bond strength. Strong base has high pH, high percent ionization, weak bond strength.

Examples Strong Acids H 2 SO 4 sulfuric HClHydrochloric HNO 3 Nitric Weak Acids H 2 CO 3 Carbonic Strong Bases NaOHSodium KOHPotassium Ca(OH) 2 ? Mg(OH) 2 ? Weak bases NH 3 Ammonia

Comparisons Acids are Sour Strong acids are corrosive Turns indicators red Reacts with metals Reacts with CO 3 Does not react with ammonium chloride Bases Bitter Strong bases are corrosive Turns indicators blue Reacts with few metals Does not react with CO 3 Reacts to make NH ` and water