Acids and Alkalis Lower Secondary Science Checkpoint 8 PDF

ACIDS AND ALKALIS Lower Secondary Science Checkpoint 8 ACIDS AND ALKALIS What are acids and alkalis? Indicators and pH scale Neutralization What is an acid? Acids are a group of chemicals that donate a proton in a reaction. What do you know about acids? Are all acids dangerous? What is an...

ACIDS AND ALKALIS Lower Secondary Science Checkpoint 8 ACIDS AND ALKALIS What are acids and alkalis? Indicators and pH scale Neutralization What is an acid? Acids are a group of chemicals that donate a proton in a reaction. What do you know about acids? Are all acids dangerous? What is an acid? everyday acids laboratory acids What is an acid? Acids are substances that: Have a pH below 7 and turn universal indicator yellow, orange or red. Properties of Acids An acid is a substance that releases hydrogen ions (H+) into an aqueous (water) solution. are corrosive. have a sour taste turn blue litmus paper red react with some metals, releasing hydrogen gas and leaving a salt behind conduct electricity are neutralized by bases, producing water and a salt. What is a strong acid? Some acids, like those found in the laboratory or a car battery, dissolve completely in solution. They are very dangerous (too dangerous to taste or touch) These acids are said to be corrosive as they can damage other materials by eating them away! They are strong acids. What is a weak acid? Many acids are found in household items such as food, drink and beauty/skincare products. These acids do not dissolve completely in solution and are known as weak acids. Working safely with acids and alkalis When you handle chemicals you should: Stand up to work, so that if you spill something it does not spill onto you Wear safety glasses, so nothing gets into your eyes Take the top off the bottle and place it upside down on the work surface, so that it does not get acid onto the surface or dirt into the acid Replace the bottle top as soon as you finish using the bottle. This prevents spills and replacing the wrong top on the wrong bottle. What are hazard symbols? How can you tell which chemicals are safe and which are dangerous? Special symbols are used on bottles and vehicles that contain dangerous chemicals. These hazard symbols show why the chemical is dangerous. Why is it important that these symbols can be recognised by people from other countries? What is an alkali? Alkalis, or bases, are another group of chemicals, the opposite of acids. Properties of Bases A base is a substance that releases hydroxide ions (OH–) in an aqueous solution. are caustic have a soapy, slimy feel turn red litmus paper blue have a bitter taste conduct electricity are neutralized by acids, producing water and a salt. What is a strong alkali? Some alkalis, like those in the laboratory or in cleaning materials such as toilet cleaner, dissolve completely in solution and are too dangerous to touch. These alkalis are said to be caustic because they can burn skin and damage other materials! They are strong alkalis, or bases.  What is a weak alkali? Alkalis are found in soaps and other materials used for cleaning. It is safe to handle these alkalis, which can feel soapy. These do not dissolve completely in solution and are known as weak alkalis, or weak bases. ACIDS AND ALKALIS What are acids and alkalis? Indicators and pH scale Neutralization What is an indicator? How can you test a liquid to find if it is an acid or an alkali? An indicator is a special chemical that changes to a different color in an acid or an alkali. Litmus paper and litmus solution are examples of indicators. What is universal indicator? Litmus is used to show if a solution is acid or alkali. Litmus does not show if the acid or alkali is weak or strong. Universal indicator has a range of colors that show how weak or strong the acid or alkali is. What is the color for a weak acid? What is the color for a strong alkali? What is the pH scale? The strength of an acid or alkali is measured by the pH scale. Each universal indicator color is given a number called the pH value. Universal indicator can tell you the pH of a solution What is the pH of a weak acid? What is the pH of strong alkali? What type of substance? Are these substances acidic or alkaline? Are they weak or strong? Substance pH Description of acid/alkali soda water 6 car battery acid 1 soap 8 washing soda 10 stomach acid 2 oven cleaner 14 vinegar 4 What type of substance? Are these substances acidic or alkaline? Are they weak or strong? Substance pH Description of acid/alkali soda water 6 very weak acid car battery acid 1 very strong acid soap 8 very weak alkali washing soda 10 weak alkali stomach acid 2 strong acid oven cleaner 14 very strong alkali vinegar 4 weak acid ACIDS AND ALKALIS What are acids and alkalis? Indicators and pH scale Neutralization Mixing an acid and an alkali What happens when an acid and an alkali are mixed? Mixing an acid and an alkali causes a chemical change. This chemical change is called a chemical reaction. How do you know this chemical reaction has taken place?  What is neutralization? The chemical reaction between an acid and an alkali is called neutralization. What happens to the pH value of the reaction mixture during neutralization? The pH value of the reaction mixture becomes closer to 7. Neutralization and indigestion Hydrochloric acid is present in our _______ (stomach, blood) to help us digest food. If too much acid is produced in the stomach it may rise into the________ (intestine, gullet). This will cause a burning feeling that is called indigestion or ________ (heartburn, peptic ulcers) Antacids are a medicine which can be taken to treat indigestion. They are a type of ________ (acid, alkali) which cancel out or neutralize the extra acid. Neutralizing stings Neutralizing the soil Soils in different places can be acidic, alkaline or neutral. Many plants do not grow well in acidic soil. Why do farmers test soil to check the pH? Farmers often add an alkali to acidic soil to make their plants grow better. How does the alkali help to treat the acidic soil? Neutralizing acid rain Gases emitted by cars, power stations and factories mix with rainwater in the atmosphere. This rainwater has a pH