Question

What is an acid? Write four properties of acids by giving examples.

Answer 1

The $pH$ scale ranges from $0{\text{ }}to{\text{ }}14$ , and most solutions fall within this range. Any solution lying below $7.0$ is considered to be acidic while above $7.0$ is alkaline. If the solution has a pH of $7.0$ then it is considered to be neutral.

Complete step by step answer:
An acid can be defined as a chemical which releases hydrogen ions in water thereby forming salts by integrating with specific metals. $pH$ scale can be used to measure acidity. On the $pH$ scale, value of $7.0$ is considered to be neutral, whereas, a value from $7.0$ to $0$ indicates increasing acidity. The properties of acids are listed below:

1. Acids react with the active metals and yield hydrogen gas. An example is shown below:
   $Zn(s) + {H_2}S{O_4}(aq) \to ZnS{O_4}(aq) + {H_2}(g)$
2. When an acid reacts with a base, they have the tendency to form a salt. An example is shown below:
   $NaOH + HCl \to NaCl + {H_2}O$
3. Acids have the tendency to change the colour of specific acid-base indicators. Most common indicators include litmus paper and phenolphthalein. Example: Blue litmus paper turns into red colour in the presence of an acid, whereas phenolphthalein turns colourless.
4. Acids possess a sour taste. Examples: Lemons containing citric acid, vinegar containing acetic acid
5. Aqueous solutions of acids are considered to be electrolytes, as they conduct an electrical current.

Note: There are certain factors that influence acidity which are: (i) Electronegativity: Acidity goes on increasing as you move from left to right in a periodic chart. (ii) Anion size: Acidity goes on increasing as you move from top to down in a periodic chart. (iii) Resonance: Anions having resonance structures are more acidic in comparison to anions which don't have.