4-Gr-7-T2-Topic-3-PPTrrrrrrrrrrt-2-v3.pptx

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1. Natural Sciences Grade 7 Term 2: Matter and Materials Acids, bases and neutrals (ppt 2)

2. Topic 3 Acids, bases and neutrals Properties of acids, bases and neutrals Natural Sciences - Grade 7

3. Properties of acids , bases and neutrals A very important group of chemicals. Found in factories and scientific laboratories. Many food and household chemicals can be classified as acids, bases and neutrals, depending on their properties. It is important to understand the properties of the chemicals in order to know which ones are dangerous / not dangerous and what they can be used for. Natural Sciences - Grade 7

4. Properties of acids Acids: are liquids. feel rough on the skin. are solutions of compounds in water. are dangerous to feel or taste, because they are corrosive. taste sour and tart. contain hydrogen ions. usually react with metals to form salts. Natural Sciences - Grade 7

5. Acids [1] Natural Sciences - Grade 7

6. Acids [2] Not all acids are dangerous. -   Useful household acids include vinegar, lemon juice, tartaric acid, citric acid powder , etc. - Vitamin C helps our immune system.  - There are other foods which are higher in vitamin C. chillies papaya guavas Natural Sciences - Grade 7

7. Acids [3] broccoli strawberries bell peppers kiwi fruits Natural Sciences - Grade 7

8. Properties of bases Feels slippery , soft or soapy on the skin. Most are dangerous to feel or taste, because they are corrosive. Taste bitter; can burn the skin; contain hydroxide ions. An alkali is a base that is soluble in water. Natural Sciences - Grade 7

9. Examples of bases Natural Sciences - Grade 7

10. Uses of bases / alkalis Natural Sciences - Grade 7 Bicarbonate of soda ( weak base): Baking. Magnesium oxide ( weak base): To treat acid indigestion and used in mouthwash. Calcium hydroxide ( strong base): Making mortar and plaster. Sodium hydroxide ( strong base): Oven cleaner. Potassium hydroxide ( strong base): Making soap.

11. Properties of neutrals Substances that are neither bases nor acids. They are not dangerous (e.g. we drink pure water; cook with cooking oil; add salt to our food; etc.). Can be made by reacting acids with bases. The bases and acids will neutralize one another and form a neutral. Natural Sciences - Grade 7

12. Examples of neutrals Cooking oil. Sugar (glucose) solution. Sodium chloride solution (salt). Pure water. Natural Sciences - Grade 7

13. The pH scale [1] Measures the strength of an acid or base. Measurement below 7 = an acid. Measurement above 7 = a base. Measurement exactly 7 = a neutral. Natural Sciences - Grade 7

14. The pH scale [2] The lower the pH value, the stronger the acid (e.g. a substance with a pH value of 1, is a stronger acid than a substance with a pH value of 4). The higher the pH value, the stronger the base (e.g. a substance with a pH value of 12, is a stronger base than a substance with a pH value of 9). Natural Sciences - Grade 7

15. The pH scale [3] Natural Sciences - Grade 7 acids alkalis neutral smaller number = stronger acid larger number = stronger alkali