Acidic and alkaline solutions
Acids
Substance producing more hydrogen ions than hydroxide ions when dissolved in water. form Having a pH lower than 7. Mixture formed by a solute and a solvent. in water. Acids produce hydrogen Electrically charged particle, formed when an atom or molecule gains or loses electrons., H+ in aqueous solution. For example:
HCl(aq) → H+(aq) + Cl-(aq)
Acidic solutions have Scale of acidity or alkalinity. A pH (power of hydrogen) value below 7 is acidic, a pH value above 7 is alkaline. values less than 7.
Alkalis
Substance producing more hydroxide ions than hydrogen ions when dissolved in water. form Having a pH greater than 7. solutions in water. Alkalis produce hydroxide ions, OH- in aqueous solution. For example:
NaOH(aq) → Na+(aq) + OH-(aq)
Alkaline solutions have pH values greater than 7.
Neutral solutions
A When a substance is neither acidic nor alkaline, and has a pH of 7. solution is neither acidic, nor alkaline. A neutral solution has a pH value of 7.
Learn more on the pH scale in this podcast.
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Indicators and the pH scale
The pH scale measures the acidity or alkalinity of a solution. The pH of a solution can be measured using a pH probe, or estimated using A chemical solution that produces many different colour changes corresponding to different pH levels. and a colour chart.
Universal indicator is one example of an acid-alkali A substance that has different colours, depending upon the pH of the solution it is in.. Indicators show whether a solution is acidic, neutral (pH 7) or alkaline. The table shows the colours for A type of indicator that can be red or blue. Red litmus turns blue in alkalis, while blue litmus turns red in acids..
| Indicator | Acidic | Neutral | Alkaline |
| Red litmus paper | Stays red | Stays red | Turns blue |
| Blue litmus paper | Turns red | Stays blue | Stays blue |
| Indicator | Red litmus paper |
|---|---|
| Acidic | Stays red |
| Neutral | Stays red |
| Alkaline | Turns blue |
| Indicator | Blue litmus paper |
|---|---|
| Acidic | Turns red |
| Neutral | Stays blue |
| Alkaline | Stays blue |