Acids & Bases Year 9 Science

Our Goals for today To determine the difference between Acids & Bases Discuss the importance of studying Acids & Bases What is the pH scale?

Why Learn about pH, Acids & Bases? Acids and bases are around us everyday A fish aquarium needs to be monitored regularly by checking its pH What do you think is the pH of tap water? The pH of a swimming pool must be checked periodically. Why? Is it important for Lakes & Rivers to maintain a certain pH?

Why is pH important? 4 Fish can’t live if the pH is too high or too low Soil has to be in a certain pH range for plants to grow and stay healthy.

pH and People 5 Water that has too high or low pH may contain harmful dissolved chemicals. Water plant operators keep a careful watch on the pH of our drinking water, to keep it safe. Heavy metals, such as lead, react to changes in pH. Environmental regulations require drinking water to remain within a specific pH range to prevent lead and other metals from dissolving out of pipes and containers and entering the water.

Acids and Bases Chemicals may be classed as acids or bases. Things that are neither acids nor bases are neutral. pH measures how acidic or basic a solution is.

What is the pH scale? The pH scale measures how acidic or basic a solution is. It is on a scale of 0-14

The pH scale The pH scale is the concentration of hydrogen ions in a given substance. The more hydrogen ions a substance has the more acidic it is.

The pH Scale Each pH unit is 10 times as large as the previous one A change of 2 pH units means 100 times more basic or acidic x10 x100

The pH Scale Careful measurement is important A mistake of one pH unit means 10 times too much or too little! x10 x100

Identifying Acids and Bases Acids have a pH from 0-7 Lower pH value indicates a stronger acid. Strong acid 0 – 3 Weak acid 3 - 7 Bases have a pH from 7-14 Higher pH value indicates a stronger base. Strong base 11 – 14 Weak base 7 - 11

Definitions of Acids and Bases A substance that will separate into ions which MUST be a hydrogen ion, H+ and another ion which can be a non-metal. A Base (alkaline) is a substance that breaks into ions.

Characteristics Of Acids Acids can be characterized by: A sour taste (eg lemons). Release hydrogen ions in water It turns blue litmus paper red They are corrosive (eat away things) They neutralise bases forming salt and water Conduct electricity

Characteristics of Bases A Base is characterized by: A bitter sour taste. (Bi-carb soda, soap) It feels slippery. (Soapy Water) It turns Red Litmus Blue. They neutralise acids

Indicators Substances that change colour in acids and bases Different types of indicators

Did we Miss something?? What happens when the pH of a substance is 7? Ans: A pH level of 7 indicates a Neutral Substance i.e: Water!

Test Your Knowledge What is the range of an ACID on the pH scale? Ans: 0-7 What is the range of a BASE and what is another name for a BASE? Ans: 7-14, Alkaline

If a stomach can digest meat, what keeps it from digesting itself If a stomach can digest meat, what keeps it from digesting itself? The human stomach uses hydrochloric acid and enzymes such as pepsin to break down and digest proteins that have entered the stomach. Gastric mucus, besides providing lubrication, lines the stomach wall and protects it from being digested by the stomach's own gastric juices. The pH in our stomachs is usually around 2. If this pH is too low (strongly acidic), the stomach wall does become vulnerable. The health of our stomachs depends on pH.

In your notebooks…. Using Science Alive Book 2 Copy the pH scale into your notebook under the heading “The pH Scale”. Draw Fig 21, p.30 and include the examples. Under this scale put the heading “Indicators”, and copy Fig 14, p.27 into your notebooks Complete in FULL sentences in your notebooks Exercises Questions 1–8 p.31