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

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

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

Natural Sciences - Grade 7 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. Strong acids: - are corrosive [acids eat through metals, stonework and clothing and it burns your skin] - are so dangerous that hazard stickers are placed on acid bottles to explain why it is dangerous - always wear safety glasses whenever you are working with strong acids - rinse your skin immediately with water [diluting and weakening the acid] under a running tap if you have spilled acid on your skin - never smell strong acids because it can damage the membranes that line the inside of your nose - turn blue litmus paper to red - are produced in our stomachs * function: break down food * as soon as some of the stomach acids move into the oesophagus then the person gets an acid reflux * the chest will experience a burning feeling * the acid level will decrease and bring some relieve if antacids like ENO, Gaviscon or Rennie are taken Natural Sciences - Grade 7

Natural Sciences - Grade 7 Acids [1] Strong acids: - are corrosive [acids eat through metals, stonework and clothing and it burns your skin] - are so dangerous that hazard stickers are placed on acid bottles to explain why it is dangerous - always wear safety glasses whenever you are working with strong acids - rinse your skin immediately with water [diluting and weakening the acid] under a running tap if you have spilled acid on your skin - never smell strong acids because it can damage the membranes that line the inside of your nose - turn Universal Indicators [strip with 6 colours above]from green to red - have a pH less than 7 - are produced in our stomachs * function: break down food * as soon as some of the stomach acids move into the oesophagus then the person gets an acid reflux * the chest will experience a burning feeling * the acid level will decrease and bring some relieve if antacids like ENO, Gaviscon or Rennie are taken Natural Sciences - Grade 7

Natural Sciences - Grade 7 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 Find more information about the Vitamin C in the following fruit and vegetables: Kiwi fruit. http://www.flickr.com/photos/dan4th/5317566258/ Broccoli. http://commons.wikimedia.org/wiki/File:Brocolli_%284700583979%29.jpg -   Natural Sciences - Grade 7

Natural Sciences - Grade 7 Acids [3] broccoli strawberries bell peppers kiwi fruits Find more information about the Vitamin C in the following fruit and vegetables: Kiwi fruit. http://www.flickr.com/photos/dan4th/5317566258/ Broccoli. http://commons.wikimedia.org/wiki/File:Brocolli_%284700583979%29.jpg -   Natural Sciences - Grade 7

Natural Sciences - Grade 7 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. Bases: - Many cleaning products contain alkalis [drain cleaners; metal polishes; abrasives; oven cleaners; all purpose cleaners; etc.]. - Bicarbonate of soda that is used for baking is in powder form. - Handy Andy, a cleaning product, often contains abase, namely ammonia. - Turn red litmus blue [test for a base] - Sodium hydroxide (caustic soda / lye) is used for the production of fabrics, paper, and cleaning agents All natural soap is made with lye (sodium hydroxide mixed with liquid). Any skin or hair cleansing product made without sodium hydroxide, is not a soap, it is a detergent.  Natural Sciences - Grade 7

Natural Sciences - Grade 7 Examples of bases Bases: - Many cleaning products contain alkalis [drain cleaners; metal polishes; abrasives; oven cleaners; all purpose cleaners; etc.]. - Bicarbonate of soda that is used for baking is in powder form. - Handy Andy, a cleaning product, often contains abase, namely ammonia. - Turn red litmus blue [test for a base] - Sodium hydroxide (caustic soda / lye) is used for the production of fabrics, paper, and cleaning agents All natural soap is made with lye (sodium hydroxide mixed with liquid). Any skin or hair cleansing product made without sodium hydroxide, is not a soap, it is a detergent.  Natural Sciences - Grade 7

Natural Sciences - Grade 7 Uses of bases / alkalis 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. Natural Sciences - Grade 7

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. Neutrals: - have no effect on litmus paper - are harmless This website has a list of other household products that will also change colour when mixed with acids or bases. Make sure you ask your parents if you may experiment before you start! http://antoine.frostburg.edu/chem/senese/101/acidbase/faq/household-indicators.shtml Natural Sciences - Grade 7

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

Natural Sciences - Grade 7 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

Natural Sciences - Grade 7 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

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