Sci 9.1 Common Acids and Alkalis (PDF)

# 9.1 Common Acids and Alkalis ## Flipped classroom Watch a video and answer the questions. ## Let's begin We can find various kinds of vinegar in a supermarket. They may have different colours but they all taste sour. They have one thing in common in their composition to give them the sour taste...

# 9.1 Common Acids and Alkalis ## Flipped classroom Watch a video and answer the questions. ## Let's begin We can find various kinds of vinegar in a supermarket. They may have different colours but they all taste sour. They have one thing in common in their composition to give them the sour taste. Do you know what it is? ## Acids and alkalis found at home All vinegars in Let's begin contain ethanoic acid*. Acids give a sour taste to different kinds of vinegar. There are many foods and drinks that also taste sour (Fig. 9.1). They also contain acids. Acids have a sour taste. Other than foods and drinks, acids are also present in some household products (Fig. 9.2). - **At least remember three:** - soft drinks - orange - lemon - kiwi fruit - yoghurt **Fig. 9.1 Foods and drinks containing acids.** **Fig. 9.2 Household products containing acids.** - hair conditioner - lotion - toilet cleaner ## Alkalis Alkalis are also commonly found in our homes. Foods such as Chinese noodles and lye water rice dumplings contain alkalis (Fig. 9.3). Some types of food containing alkalis have a bitter taste. In addition to foods, many household products also contain alkalis (Fig. 9.4). **Fig. 9.3 Foods containing alkalis.** - baking soda - lye water rice dumpling - preserved duck eggs - Chinese noodles **Fig. 9.4 Household products containing alkalis.** - kitchen cleaner - bleach - alkaline batteries - toothpaste - soap **Alkalis give a slippery feel. It is similar to the feel when you wash your hands with soap.** ## Link The corrosive nature of acids and alkalis, and the potential dangers in handling them will be discussed in Section 9.4 (p. 45) and 9.6 (p. 63). **Fig. 9.5 We feel slippery when washing hands with soap.** Note that many acids and alkalis (such as those in household cleaners) are irritant or even corrosive. We should handle them with care and never taste them except those in food. - Acids have a **sour** taste. - Alkalis give a slippery feel. Some of them have a **bitter** taste. ## Acids and Alkalis found in laboratory ### Common acids and alkalis used in laboratory We often use acids and alkalis in the laboratory. Fig. 9.6 shows some common acids found in the laboratory. They are hydrochloric acid*, sulphuric acid* and nitric acid*. **Fig. 9.6 Acids commonly used in the laboratory.** - dilute hydrochloric acid - dilute sulphuric acid - dilute nitric acid **Nitric acid is stored in dark-coloured reagent bottles because it is easily decomposed by light.** ### Fig. 9.7 shows some common alkalis found in the laboratory. They are sodium hydroxide*, ammonia solution* and calcium hydroxide* (lime water). **Fig. 9.7 Alkalis commonly used in the laboratory.** - dilute sodium hydroxide solution - dilute ammonia solution - lime water **Most acids and alkalis used in the laboratory are irritant or even corrosive. Safety precautions must be taken when handling them.** ## Safety precautions when handling acids and alkalis in laboratory In the following sections, we will handle acids and alkalis in the laboratory. We must strictly follow the laboratory safety rules below in the practicals. - **Read the hazard warning symbols on the bottles of chemicals carefully. Identify the risks of handling them.** - **Wear a laboratory coat and disposable or protective gloves.** - **Wear safety spectacles.** - **Do NOT mix acids or alkalis with any other chemicals without getting approval from your teacher.** - **Pour waste solutions into suitable waste bottles. Do NOT pour them into the sink.** - **Wash your hands thoroughly after handling acids or alkalis.** ## Emergency treatment for accidents involving acids and alkalis If accidents involving acids or alkalis occur in the laboratory, keep calm and report them to the teacher at once. Some emergency treatments are discussed below. If the accident is serious, the injured person should be taken to hospital as soon as possible. | **In case acids or alkalis splash onto...** | **Action** | |---|---| | Your skin | Immediately wash the affected area under slow-running water for at least 10 minutes. | | Your eyes | Immediately wash the affected eye(s) using an eye wash bottle for at least 10 minutes. | | Your clothes | Carefully remove the affected clothes and avoid making contact with any acids or alkalis on the clothes. | **Acids and alkalis can be irritant or corrosive. We must handle them with care and take safety precautions.** ## Uses of acids and alkalis Acids and alkalis are widely used in daily life. Some examples are shown below. ### Uses of acids - **For food preservation** - The action of microorganisms in food may make the food turn bad. - As most microorganisms cannot grow in acidic conditions, acids can be used to preserve food. - Vinegar is acidic. It is commonly used to preserve vegetables. - **Fig. 9.8 Cucumbers preserved in vinegar.** - **For stain removal** - Hydrochloric acid is present in many toilet cleaners. It can react with dirt and stains in the toilet bowl. - The products of the reactions are easily removed when we flush the toilet. - **Fig. 9.9 A toilet cleaner containing hydrochloric acid.** ### Uses of alkalis - **For making noodles** - Lye water is an alkaline solution. - It is often added to Chinese noodles during production to make the noodles chewy in texture. - **Fig. 9.10 Lye water is added to noodles to make them more chewy.** - **For grease removal** - Sodium hydroxide is present in many kitchen cleaners. It can react with grease on kitchen stoves. - The products of the reactions can be easily wiped or washed away with water. - **Fig. 9.11 A kitchen cleaner containing sodium hydroxide.** **Acids and alkalis are widely used in daily life.** ## After-class activity Search for more examples of the uses of acids and alkalis in our daily life. * means ethanoic acid, hydrochloric acid, sulphuric acid, nitric acid, sodium hydroxide, ammonia solution and calcium hydroxide. * is a mark at the end of this sentence. **Section Summary 9.1** | **Characteristic** | **Acids** | **Alkalis** | |---|---|---| | | • Have a sour taste | • Give a slippery feel | | | | • Some have a bitter taste | | Examples of acids and alkalis in laboratory | • Hydrochloric acid | • Sodium hydroxide | | | • Sulphuric acid | • Ammonia solution | | | • Nitric acid | • Calcium hydroxide (lime water) | | Examples of common uses | • Vinegar for food preservation | • Lye water for making noodles chewy | | | • Toilet cleaners for stain removal | • Kitchen cleaners for grease removal |